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241 9 DESIGN GUIDELINES FOR BARRIER-MOMENT SLAB SYSTEMS MOUNTED ON MSE WALLS FOR TL-3 THROUGH TL-5 IMPACTS The format presented in this section follows Chapter 7 of the NCHRP Report 663, âDesign Guidelinesâ (2). The research documented in that report was limited to TL-3 impacts. The information presented herein includes updated TL-3 impact guidelines and extends the guidelines to TL-4 and TL-5 impacts. The TL-3 impact guidelines are updated based on data from a numerical simulation with an updated TL-3 truck in conformance with MASH (5) requirements. The design guidelines for the TL-4 impact were developed based on the data collected from the full-scale impact test and from the numerical simulations. The design guideline for TL-5 impact were developed based on data collected from the full-scale crash test, static test, and the numerical simulations. The FE analyses were conducted using vertical wall barriers. However, the results should be applicable to other common barrier types. The design guidelines address the BMS system and the MSE wall reinforcement. The guidelines are set in terms of AASHTO LRFD practice. The AASHTO LRFD formatted version of the design guidelines are presented in Chapter 10. An example of the application of the design guidelines for the MSE wall and barrier system used in the TL-5 crash test is presented in Appendix D. During an impact, the displacement of the BMS system occurs in the form of sliding and rotation. For rotational displacements, two points of rotation are considered as shown in Figure 9-1. The point of rotation should be determined based on the interaction between the barrier coping and top of the wall panel. With reference to Figure 9-1, point of rotation A should be used if the top of the wall panel is not in contact with the coping due to the presence of an air gap or sufficiently compressible material (with a thickness greater than 0.75 in based on current practice). Point of rotation B should be used if there is direct bearing between the bottom of the coping and the top of the wall panel or level-up concrete. For a given BMS system, rotation point B will provide a greater static resistance to overturning than rotation point A. As a result, for the same impact, a wider moment slab will be required for systems rotating around point A than for those rotating around point B to limit the overturning displacements. The sliding requirement must also be checked. The required moment slab width is determined by applying the equivalent static load to the barrier at its resultant height (He) and using equilibrium equations to evaluate both sliding and overturning modes (Figure 9-2). The recommended equivalent static load was based on the static resistances of selected TL-3, TL-4 and TL-5 BMS systems as explained later in this chapter. For the TL-3, TL-4-1. TL-4-2 and the TL-5-1 systems selected, the static resistance to rotation was deemed more critical during the vehicle impact, as demonstrated through crash testing and numerical simulations. For the TL-5-2 system selected, the resistance to sliding was found out to be more critical. The required moment slab width that is calculated in accordance with these guidelines corresponds to the controlling failure mode and will be the larger of the two widths required to accommodate sliding and overturning.
242 Rotation Point B Rotation Point A Overburden Soil Moment Slab Traffic Barrier C.G. Panels Finished Grade Figure 9-1 Rotation points for design of BMS system.
243 Equivalent Static Load, L hh Leveling Pad Overburden Soil BA W lA lB Moment Slab Traffic Barrier C.G. Panels s Finished Grade He FSRotationPoint A Rotation Point B Equivalent Static Load, L hh Leveling Pad Overburden Soil BA W lA lB Moment Slab Traffic Barrier C.G. Panels s Finished Grade He FSRotationPoint A Rotation Point B Figure 9-2 Application of static equivalent load on BMS system.
244 9.1 Guidelines for the Barrier The barrier, coping, and moment slab system should be designed for both strength and stability. The barrier should be designed in accordance with AASHTO LRFD to have an ultimate strength capable of resisting the dynamic impact load, Ld, recommended in this report and summarized in Table 9-1. Any section within the coping and the moment slab should not fail in flexure when the barrier is subjected to the design impact load. In addition to the structural capacity, the BMS system must be able to resist the two modes of stability failure (sliding and overturning) when the static equivalent load, Ls, is applied. Both the dynamic impact load and static equivalent load are applied at a resultant height, He. 9.1.1 Sliding of the Barrier The factored static resistance (Ï P) to sliding of the BMS system along its base should be greater than or equal to the factored equivalent static load (γ Ls) due to the dynamic impact force. Ï P ⥠γ Ls (9-1) The equivalent static load, Ls, is determined from Table 9-1, the resistance factor Ï is 1 (AASHTO LRFD 10.5.5.3.3), and the load factor γ is 1.0 (extreme event). Table 9-1 Recommended equivalent static load (Ls) for TL-3 through TL-5. Test Designation Ld (1) (kips) Ls(2) (kips) Hmin (3) (in.) He (4) (in.) Wmin (5) (ft) BL(6) (ft) TL-3(7) 70 23 32 24 4 10 TL-4-1 70 28 36 25 4.5 10 TL4-2 80 28 >36 30 4.5 10 TL-5-1 160 80 42 34 7 15 TL-5-2 260 132 >42 43 12 15 (1) Dynamic Load Ld (2) Equivalent static load (Ls) applied at height He, calculated based on the static resistance deemed more critical for the barrier as follows: the overturning resistance for TL-3, TL-4 and TL-5-1 barriers and the sliding resistance for TL-5-2 barrier. (3) Minimum barrier height Hmin (4) Effective barrier height He (5) Minimum moment slab width Wmin (6) Minimum length of the precast barrier BL (7) Revised from the recommendations in NCHRP Report 663, Figure 7.1 (2) The static resistance P should be calculated as: P = W tan Ïr (9-2)
245 where W = weight of the monolithic section of barrier and moment slab plus any material laying on top of the moment slab (kips) Ïr = friction angle of the soil - moment slab interface The factored equivalent static load should be applied to the length of the moment slab between joints. Any coupling between adjacent moment slabs or friction that may exist between free edges of the moment slab and the surrounding soil should be neglected. If the soilâmoment slab interface is rough (e.g., cast in place), Ïr is equal to the friction angle of the soil Ïs. If the soilâ moment slab interface is smooth (e.g., precast), Ïr should be reduced accordingly ( 2tan tan 3r s Ï Ï= ). 9.1.2 Overturning of the Barrier The factored static moment resistance (ÏM) to overturning of the BMS system should be greater than or equal to the factored static load (γ Ls) due to the impact force times the moment arm hA or hB. The moment arm is taken as the vertical distance from the point of impact due to the dynamic force (effective height, He) to the point of rotation A or B ( Figure 9-2). Ï M ⥠γ Ls (hA or hB) (9-3) The static load, Ls, is determined from Table 9-1, the resistance factor Ï is 1 (AASHTO LRFD Table 10.5.5.3.3), and the load factor γ is 1.0 (extreme event). M should be calculated as: M = W (lA or lB) (9-4) where W= weight of the monolithic section of barrier and moment slab plus any material lying on top of the moment slab (kips) lA or lB = horizontal distance from the CG (c.g.) of the weight W to the point of rotation A or B (ft) The moment contribution due to any coupling between adjacent moment slabs, shear strength of the overburden soil, or friction that may exist between the backside of the moment slab and the surrounding soil should be neglected. 9.1.3 Rupture of the Coping in Bending The critical section of the coping (Figure 9-3) must be designed to resist the applicable dynamic impact load conditions for the appropriate test level as defined in Table 9-1. The load to be considered for this design is the dynamic load Ld in Table 9-1.
246 Leveling Pad Rotation Point A Overburden Soil Moment Slab Traffic Barrier C.G. Panels Finished Grade Rotation Point B Critical Section Leveling Pad Rotation Point A Overburden Soil Moment Slab Traffic Barrier C.G. Panels Finished Grade Rotation Point B Critical Section Figure 9-3 Coping and possible weakest section.
247 9.2 Guidelines for the Wall Reinforcement The wall reinforcement guidelines should ensure that the reinforcement does not pullout or break during a barrier impact with the chosen design vehicle. The connection between the reinforcement and the wall panel should be able to resist the pullout load or breaking load whichever controls. 9.2.1 Pullout of the Wall Reinforcement a) Pressure Distribution Approach Since no difference was found between the static pullout capacity and the dynamic pullout capacity of reinforcing strips or bar mats (2), the capacity of the reinforcing strips or bar mats should be calculated by common static methods and should be compared to the impact loads obtained from the pressure distributions recommended herein The factored static resistance (Ï P) to pullout of the reinforcement should be greater than or equal to the sum of the factored static load (γs Fs) due to the earth pressure and the factored dynamic load (γd Fd) due to the impact. The static load Fs should be obtained from the static earth pressure ps times the tributary area At of the reinforcement unit. The dynamic load Fd should be obtained from the pressure pd of the pressure distribution in Table 9-2 and Figure 9-4 times the tributary area At of the reinforcement unit. Ï P ⥠γs Fs + γd Fd (9-5) Ï P ⥠γs p s At+ γd pdp At (9-6) For TL-3 through TL-5, the dynamic pressure pdp is given in Table 9-2 and Figure 9-4, the resistance factor Ï is 1 (AASHTO C11.5.8), the load factor γd is 1.0, and the load factor γs is also 1.0. Table 9-2 Design pressure pdp for reinforcement pullout and tributary height Test Designation First Layer Second Layer pdp-1 (psf) h1 (ft) pdp-2 (psf) h2 (ft) TL-3(1) 370 2.25 165 2.5 TL-4-1 370 2.25 270 2.5 TL-4-2 370 2.25 270 2.5 TL-5-1 725 1.6 400 2.5 TL-5-2 1240 1.6 680 2.5 (1) Revised from NCHRP Report 663, Figure 7.4 (1)
248 Traffic Barrier C.G. h h Moment Slab Soil Top Layer of Reinforcement Second Layer of Reinforcement p dp-1 p dp-2 p s 1 2 Figure 9-4 Pressure distribution pdp for reinforcement pullout. The resistance P for one strip should be calculated as (AASHTO LRFD Eq. 11.10.6.3.2- 1): P = F* Ïv 2b L (9-7) where F*= resistance factor (sliding plus bearing) obtained from the current AASHTO LRFD (Figure 9-5). Ïv= vertical effective stress on the reinforcement b= width of the strip L= full length of the strip. The resistance P for bar mats should be calculated as: P = F* Ïv Ï D n L (9-8) where D= diameter of the bar mats, and n= is the number of longitudinal bars in one bar mat unit.
249 Figure 9-5 Default values for the pullout friction factor, F* (AASHTO LRFD Figure 11.10.6.3.2-1) (3). b) Line load approach The factored static resistance (Ï P) to pullout of the reinforcement unit should be greater than or equal to the sum of the factored static load (γs Fs) due to the earth pressure and the factored dynamic load (γd Fd) due to the impact. The static load Fs should be obtained from the static earth pressure ps times the tributary area At of the reinforcement unit. The dynamic impact load Fd should be obtained from the line load Qdp times the longitudinal spacing (SL) of the reinforcement units. Ï P ⥠γs Fs + γd Fd (9-9) Ï P ⥠γs p s At + γd Qdp SL (9-10) For TL-3 through TL-5, Qdp is given by the line load shown in Table 9-3 and Figure 9-6; the resistance factor Ï is 1 (AASHTO C11.5.8), the load factor γd is 1.0 (extreme event), and the load factor γs is 1.0.
250 Table 9-3 Design line load Qdp for reinforcement pullout Test Designation Line Load (lb/ft) First Layer, Qdp-1 Second Layer, Qdp-2 TL-3(1) 835 415 TL-4-1 835 675 Tl-4-2 835 675 TL-5-1 1160 1000 TL-5-2 1990 1700 (1) Revised from NCHRP Report 663, Figure 7.6 (1) Traffic Barrier C.G. Moment Slab Soil Top Layer of Reinforcement Second Layer of Reinforcement p s Qdp-1 Qdp-2 < 1 ft < 2.7 ft Figure 9-6 Line Load Qdp for reinforcement pullout. The reinforcement resistance P for strips should be calculated as (AASHTO LRFD Eq. 11.10.6.3.2-1): P = F* Ïv 2b L (9-11) where F*= resistance factor (sliding plus bearing), obtained from the current AASHTO LRFD guidelines (3) (Figure 9-5). Ïv= vertical effective stress on the reinforcement b= width of the strip L= full length of the reinforcement
251 The reinforcement resistance P for bar mats should be calculated as: P = F* Ïv Ï D n L (9-12) where D= diameter of the bar mats, and n= number of longitudinal bars within one bar mat unit. 9.2.2 Yield of the wall Reinforcement a) Pressure Distribution The factored resistance (Ï R) to yield of the reinforcement should be greater than or equal to the sum of factored static load (γs Fs) due to the earth pressure and the factored dynamic load (γd Fd) due to the impact. The static load Fs should be obtained from the static earth pressure ps times the tributary area At of the reinforcement unit. The dynamic load Fd should be obtained from the dynamic pressure pdy of the pressure distribution (Table 9-4 and Figure 9-7) times the tributary area At of the reinforcement unit. It is expressed as: Ï R ⥠γs Fs + γd Fd (9-13) Ï R ⥠γs ps At + γd pdy At (9-14) For TL-3 through TL-5, pdy is given by the pressure distribution shown in Table 9-4 and Figure 9-7, the resistance factor Ï is 1 (AASHTO C11.5.8), the load factor γd is 1.0, and the load factor γs is 1.0. Table 9-4 Design pressure pdy for reinforcement yield Test Designation First Layer Second Layer pdy-1 (psf) h1 (ft) pdy-1 (psf) h2 (ft) TL-3(1) 1415 2.25 300 2. 5 TL-4-1 1755 2.25 300 2.5 TL-4-2 1755 2.25 300 2.5 TL-5-1 3250 1.6 485 2.5 TL-5-2 4440 1.6 675 2.5 (1) Revised from NCHRP Report 663, Figure 7.7 (2)
252 Traffic Barrier C.G. h h Moment Slab Soil Top Layer of Reinforcement Second Layer of Reinforcement p dy-1 p dy-2 p s 1 2 Figure 9-7 Pressure distribution pd for reinforcement yield. The reinforcement resistance R for strips or bar mats should be calculated as: t sR AÏ= (9-15) where Ït= tensile strength of the reinforcement, and As= cross section area of the reinforcement. s cA b E p e r S tr ip= à (9-16) where Ec= strip thickness corrected for corrosion loss. (AASHTO LRFD Figure 11.10.6.4.1-1) b = strip width (AASHTO LRFD Figure 11.10.6.4.1-1) *2 4s DA Ï= for Bar mats (9-17) where D*= diameter of bar or wire corrected for corrosion loss. (AASHTO LRFD Figure 1.10.6.4.1-1). a) Line load approach The factored resistance (Ï R) to yield of the reinforcement should be greater than or equal to the sum of factored static load (γs Fs) due to the earth pressure and the factored dynamic load (γd Fd)
253 due to the impact. The static load Fs should be obtained from the static earth pressure ps times the tributary area At of the reinforcement unit. The dynamic load Fd should be obtained from the line load Qdy times the longitudinal spacing (SL) of the reinforcement. Ï R ⥠γs Fs + γd Fd (9-18) Ï R ⥠γs p s At + γd Qdy SL (9-19) For the load levels TL-3 through TL-5, Qdy is given by the line load shown in Table 9-5 and Figure 9-8, the resistance factor Ï is 1 (AASHTO C11.5.8), the load factor γd is 1.0, and the load factor γs is 1.0. Table 9-5 Design line load Qd for reinforcement yield Test Designation Line Load (lb./ft) First Layer, Qdy-1 Second Layer, Qdy-2 TL-3(1) 3185 750 TL-4-1 3950 750 TL-4-2 3950 750 TL-5-1 5200 1215 TL-5-2 7105 1690 (1) Revised from NCHRP Report 663, Figure 7.8 (2) Traffic Barrier C.G. Moment Slab Soil Top Layer of Reinforcement Second Layer of Reinforcement p s Qdy-1 Qdy-2 < 1 ft < 2.7 ft Figure 9-8 Line Load Qdy for reinforcement yield.
254 The reinforcement resistance R for strips or bar mats should be calculated as: t sR AÏ= (9-20) where Ït= tensile strength of the reinforcement, and As= cross section area of the reinforcement. s cA b E per Strip= Ã (9-21) where Ec= strip thickness corrected for corrosion loss (AASHTO LRFD Figure 11.10.6.4.1-1). b = unit width of reinforcement (AASHTO LRFD Figure 11.10.6.4.1-1). *2 4s DA Ï= for Bar mats (9-22) where D*= diameter of bar or wire corrected for corrosion loss. (AASHTO LRFD Figure 11.10.6.4.1-1). 9.3 Data to Back up Guidelines for TL-3 throughTL-5 The information presented in this section represents background data used to finalize the recommended loads and pressures for the design of the barrier, moment slab and wall reinforcement. The limit states considered in the preparation of the guidelines are described, as well as the general procedure followed in the determination of the loads used in the process. This is followed by data to back up the guidelines for each of the test levels of interest (TL-3, TL-4 and TL-5). 9.3.1 Limit States The analysis of the systems subject to vehicle collision is done using resistance factors and load factors specified in AASHTO LRFD for an Extreme Event Type II. The behavior of the different system components was evaluated at the extreme event limit state to avoid the following: 1. Failure of the barrier during impact: Yield line analysis was carried out, a Load factor of 1 (extreme event) and Resistance factor of 1 were used, with the nominal resistance of the barrier calculated through an equation based on AASHTOâs recommendations.
255 2. Failure of the coping during impact: strength analysis is carried out as recommended by AASHTO. 3. Yielding of the soil reinforcement during impact: A load factor of 1 (extreme event) and a resistance factor of 1 were used. 4. Pullout of the soil reinforcement during impact: A Load factor of 1 (extreme event) and a Resistance factor of 1 were used. Based on the analysis of crash test and simulation results, the results from selected systems for the test levels TL-3 through TL-5 were considered in the preparation of the design guidelines. These systems satisfy limiting displacement values that were developed by considering the vehicle behavior during all crash tests, all numerical simulations, and minimizing the need for repair after the impact. These limiting displacement values are: 1. Maximum dynamic displacement at the top of the barrier during impact = 1.0 in. (25.4 mm) for TL-3, 1.5 in. (38 mm) for TL-4, and 1.75 (44.5 mm) for TL-5 barrier. This corresponds to a maximum barrier rotation angle of about 2 degrees and varies due to the barrier height associated with each test level. 2. Maximum permanent displacement at the coping level of the barrier after impact less than 1 in. (25 mm) 9.3.2 General procedure for load determination The loads recommended for design include dynamic loads and equivalent static loads. They address the same strength limit states and serviceability limit states as above. 1) Dynamic Load on Barrier The dynamic load on the barrier is the best estimate of the load perpendicular to the barrier generated by the impacting vehicle. This load is used for the strength limit state of the barrier and of the coping. The magnitude and the height of application of the dynamic loads for test levels TL- 3, TL-4 and TL- 5 were selected based on a combination of FE analyses and the crash test results. The advantage of the FE analyses is that the actual dynamic load at the contact between the barrier and the truck can be identified precisely, yet the reliability of the simulation results depends on the validity of the models used and the computations made. On the other hand, the crash test is a real event, but the load is calculated based on assumptions of mass associated with the accelerations measured at a specific point. In the end, the loads from the numerical simulations were favored, and the full-scale crash tests provided a verification of the numerical results. Chapter 3 presents the FE analysis for TL-3 with the updated pickup truck model that conforms to the 2270P vehicle recommended by MASH (5). This led to revising the dynamic load from 54 kips (240 kN) recommended in NCHRP 663 to 70 kips (311 kN). The impact of the barrier height on the resulting dynamic load was inspected for TL-4 and TL-5 in Chapter 3. As a result, TL-4 and TL-5 loads were divided into two categories each in order to account for the increase in load observed with an increase in barrier height. The need for such a distinction was not as clear for TL-4 as it was for TL-5.
256 2) Equivalent Static Load on the Barrier The equivalent static load on the barrier is the best estimate of the load that should be used in design to obtain a barrier moment slab system that satisfies the serviceability limit state. These limit states include sliding and overturning. The limit state deemed more critical was selected to calculate the equivalent static loads. These loads were determined in three steps. First the barrier moment slab system that satisfied the serviceability criteria was determined; this was done by studying the results of numerical simulations and crash tests. Second the ultimate resistance that could be developed by that system was determined for both sliding and overturning and compared. Point B was considered in the resistance to rotation calculations since the BMS systems considered all rotated around point B. The more critical mode of failure (sliding/ overturning) was used in the third step. Third the critical ultimate resistance was multiplied by a resistance factor equal to 0.8 to obtain the equivalent static loads. For TL-3 through TL5-1, the static resistance to rotation was found to be critical for the selected systems. For TL-5-2, sliding was found to be critical. 3) Dynamic Load on Reinforcement Strip for Pullout The dynamic design load LDP for reinforcement pullout is the load that needs to be considered in the pullout design of the reinforcement for the reinforcement to perform satisfactorily during an impact. This load was obtained using the following steps: 1. The maximum dynamic load Fmd applied to 10 ft long strips in numerical simulations and/or crash tests was selected; the reason for choosing 10 ft strips is that this length led to an acceptable behavior of the barrier-moment slab-wall system during crash tests and numerical simulations. The only exception was TL-5-2, for which 16 ft strips were used in order to limit wall displacements. A maximum wall displacement of 0.75 in. (19.05 mm) was considered to define what is acceptable. 2. The strip load due to the static earth pressure Fep was added to Fmd. 3. Then, the total load (Ft = Fmd + Fep) was compared to the maximum static resistance P for the chosen strip calculated according to the AASHTO LRFD equation 9.11. a. If Ft > P, then LDP = P â Fep, where 0.8 is the pullout resistance factor. b. If Ft < P, then LDP = Ft â Fep 4. Fourth, the dynamic design load LDP was divided by the tributary area of the strip to obtain a dynamic design pressure (pd ) and a corresponding dynamic design line load (Qd ). The loads should be resisted while satisfying the pullout limit state design. 4) Dynamic Load on Reinforcement Strip for Yielding The dynamic design load LDY for yielding of the reinforcement is the load that needs to be considered in the design against yielding of the reinforcement for the reinforcement to perform satisfactorily during an impact. This load was obtained by selecting the maximum dynamic strip load found in the crash tests and in the numerical simulations. Note that the numerical simulations involved different strip lengths and that often the longer lengths gave the highest loads.
257 9.3.3 Selection of Serviceability Limits The selection of serviceability limits was based on analysis of data from the crash tests and the FE impact simulations of different BMS systems for all test designations. This section describes the process of selecting an acceptable maximum dynamic and permanent movement for a BMS system at which the system is still considered serviceable. The two main considerations were: the overall satisfactory performance of the BMS system, and the absence of significant damage to the panels such that no replacement would be necessary after an impact. The goal was to choose a BMS system that would meet the chosen tolerable displacements, and to calculate the equivalent static load as described in section 9.3.2 for the chosen system. 1) Maximum Dynamic Displacement Value A maximum dynamic displacement of 0.5 in. (12.7 mm) at the top of the barrier was initially selected as the criterion for TL-3. However, the TL-3 crash test performed satisfactorily although a maximum dynamic movement of 0.84 in. (21.33 mm) was observed at the top of the TL-3 barrier during the crash test. As a result, the researchers adopted a less stringent criterion of 1 in. (25.4 mm) movement at the top of the barrier. This value was revised again because the simulation results for the TL-4 and TL-5 test designations showed acceptable impact performance with dynamic displacement at the top of the barrier greater than one inch. It was noted that the barrier height requirement increases by test level and that the same angle of barrier rotation will result in an increase in the deflection of the top of the barrier. Table 9-6 presents maximum dynamic displacements obtained at the top of barrier, coping and bottom of coping levels for TL-3 through TL-5 barriers as defined in Figure 9-9. The highlighted rows in Table 9-6 present the crash test and corresponding simulation displacement results. With reference to Table 9-6, the maximum dynamic displacements at the top of the simulated barriers decrease with an increase of the moment slab width. The moment slab widths simulated were 3.5 ft (1.06 m), 4 ft (1.22 m) and 4.5 ft (1.37m) for TL-3, 4.5 ft (1.37 m) and 5 ft (1.52 m) for TL-4, 7 ft (2.13 m) for TL-5-1, and 9 ft (2.74 m) and 12 ft (3.66 m) for TL5-2. The length of the simulated moment slabs was 30 ft (9.14 m) in all cases. The maximum dynamic displacements at the barrier top were: - For TL-3: 1.5 in. (38.1 mm), 1.06 in. (26.9 mm) and 0.893 in. (22.7 mm) for moment slab widths of 3.5 ft (1.06 m), 4.0 ft (1.22 m) and 4.5 f. (1.37 m), respectively. - For TL-4: 1.5 in. (38.1 mm) and 0.71 in. (18.0 mm) for moment slab widths of 4.5 ft (1.37 m) and 5 ft (1.52 m), respectively. - For TL-5-1: 2.13 in. (54.1 mm) and 1.54 in. (39.1 mm) for a 7 ft (2.13 m) moment slab width and a vertical wall and NJ profile barrier geometry, respectively. This difference in barrier displacement is attributed to the difference in static resistance to rotation between the two barrier sections. The change in barrier geometry results in a 14% increase in static rotational resistance from 70 kips (311 kN) for the vertical wall barrier to 80 kips (356 kN) for the NJ profile barrier (which was crash tested). - For TL-5-2: 2.66 in. (67.6 mm) and 1.73 in. (43.9 mm) for moment slab widths of 9 ft (2.74 m) and 12 ft (3.66 m), respectively.
258 Table 9-6 Summary of crash test barrier and simulation displacement results Test Level Description Moment Slab Length (ft) Moment Slab Width a (ft) Max Dynamic (in) Max Permanent (in) Top Bottom Coping Top Bottom Coping TL-3 (32 in)b Simulation (Vertical wall) 30 3.5 1.5 0.67 0.83 0.73 0.63 0.67 Simulation (Vertical wall) 30 4 1.06 0.67 0.67 0.67 0.63 0.63 Simulation (Vertical wall) 20 4.5 0.996 0.735 0.757 0.716 0.696 0.7 Crash Test (Vertical wall) 30 4.5 0.84 0.54 0.55 0.37 0.25 c 0.25 Simulation (Vertical wall) 30 4.5 0.893 0.715 0.716 0.73 0.71 0.71 TL4-1 (36 in)b Simulation (Vertical wall) 30 4.5 1.5 0.91 0.98 0.83 0.79 0.79 Crash Test (Single slope) 30 5 0.5 0.4 0.4 0.2 0.31 0.28 Simulation (Single slope) 30 5 0.71 0.59 0.59 0.28 0.43 0.43 TL4-2 (42 in)b Simulation (Vertical wall) 30 4.5 1.5 0.72 0.77 0.71 0.67 0.69 TL5-1 (42 in)b Simulation (Vertical wall) 30 7 2.13 1.06 1.14 1.54 0.98 0.98 Crash Test (NJ profile) 30 7 _ d 1.06 0.44 0.48c Simulation (NJ profile) 30 7 1.54 0.63 0.83 0.87 0.59 0.63 TL5-2 (>42 in)b Simulation (Vertical wall) 30 9 2.66 1.77 1.95 1.73 1.65 1.69 Simulation (Vertical wall) 30 12 1.73 0.75 0.83 1.34 0.67 0.69 a Moment slab width measured from the roadside face of the panel. b Barrier height measured from finished ground level. c Result interpolated based on the top barrier displacement and barrier geometry d Data not available due to technical difficulties.
259 Figure 9-9 Locations of displacement measurements. Based on these results, it was decided to assign an allowable maximum dynamic displacement at the top of the barrier for each of the test levels. For this purpose, five factors were taken into consideration. The first factor is the increase in maximum dynamic displacement at the top of the barrier as a function of barrier height for a given angle of rotation as illustrated in Figure 9-10. Second, based on the analyzed barrier systems, rotational displacement is generally more prominent than sliding displacement for TL-3, TL-4 and TL-5-1. This can be explained by the higher static resistance to sliding than rotation for the systems considered. For the TL-5-2 system with 12-ft moment slab width, the resistance to sliding is less than the resistance to rotation. Third, the barrier displacement versus time curves were plotted and compared to determine the displacement trends for each of the test levels. Fourth, based on the data from the numerical simulations, the BMS systems for the TL-3 and TL-4-1 crash tests were considered to be conservative from a serviceability point of view. Indeed, the truck was successfully contained and redirected without any damage to the underlying MSE wall. Fifth, the maximum dynamic displacements obtained in the simulations were in general agreement with those obtained in the crash tests. This increased the confidence in the simulation results. Based on these considerations, the maximum dynamic displacements at the top of the barrier selected for TL-3, TL-4, and TL-5 were 1 in. (25.4 mm), 1.5 in. (38.1 mm), and 1.75 in. (44.45 mm) respectively. The maximum displacements at the top level of the barrier for each for these systems are presented as a function of time in Figure 9-11. The curves show the predicted maximum dynamic displacements and the permanent displacement at the end of the time displacement history. 2) Maximum Permanent Displacement Value The permanent displacements at the coping level were also considered. In the three crash tests, the barrier displacements at the coping level were 0.25 in. (6.35 mm), 0.28 in. (7.11 mm) and 0.48 in. (12.20 mm) corresponding to TL-3, TL-4-1, and TL5-1 with moment slab widths of 4.5 ft (1.37 m), 5.2 ft (1.58 m) and 7 ft (2.13 m) respectively. Since the TL-3 and the TL-4-1 crash tests were considered conservative, the TL-5-1 crash test was more heavily considered.
260 Figure 9-10 Difference in dynamic displacements at the barrier top for the same angle of rotation. Figure 9-11 Barrier displacements at the top level of the adopted BMS systems for static load calculations. The TL5-1 barrier and wall system performed adequately with only minor damage to the wall panels. The damage was in the form of hairline cracks that were observed in two of the panels at the level of the first layer of reinforcement strips. The panels were still considered serviceable and to have retained their structural integrity. As a result, the barrier displacements observed in this crash test and the corresponding simulation results were considered more informative and used to establish the recommendations for acceptable barrier displacements. -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 0 0.2 0.4 0.6 0.8 1 1.2 Di sp la ce m en t ( in ) Time (s) Max Displacements top TL3-T-4.0 TL4-1-T-4.5 TL4-2-T-4.5 TL5-1-T-7 TL5-2-T-12 Maximum TL-4- 1.5 in. Maximum TL-5-1.75 in. Maximum TL-3-1.0 in.
261 The maximum permanent movement in the TL5-1 crash test barrier was 1.06 in. (26.9 mm) at the top of the barrier and 0.48 in. (12.2 mm) at the coping section of the barrier. The corresponding simulation predicted 0.87 in. (22.1 mm) at the top and 0.63 in. (16.0 mm) at the bottom of the barrier. Given the use of FE simulations in guiding the choice of adequate BMS systems, the fact that the simulation results tend to over-predict the permanent barrier displacement, and the good results obtained in the TL5-1 crash test, a value of 1 in. (25.4 mm) was considered as the maximum permanent displacement value. Figure 9.12 shows the displacement versus time curves obtained from simulations of TL-3 through TL-5 systems that were adopted for the calculation of equivalent static loads. The displacements curves presented correspond to the points at which maximum displacements were obtained. The permanent displacements are represented by black dots on the curves. Figure 9-12 Barrier displacements at coping level of adopted BMS systems for static load calculations. 3) Systems that Satisfy Serviceability Criteria Table 9.7 shows the moment slab widths that were considered in the static resistance calculations for each test level, and their corresponding resistance values. These moment slab widths were selected as minimum widths for their corresponding test levels. The selection process for each of the test levels is presented in the following sections. The chosen TL-3 and TL-4-1 moment slab widths are slightly less conservative than those crash tested (i.e., they have a shorter width moment slab). For TL-5-1, the selected moment slab width corresponds to the system that was crash tested. For TL-5-2, a 12 ft moment slab width was adopted based on achieving successful impact performance and satisfying the selected displacement criteria. -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 0.2 0.4 0.6 0.8 1 1.2 Di sp la ce m en t ( in ) Time (s) Barrier Displacements at Coping Level TL3 / 4.0 ft TL4-1/ 4.5 ft. TL4-2-/ 4.5 ft. TL5-1/ 7.0 ft TL5-2/ 12.0 ft Maximum Value- 1 in.
262 Table 9-7 Selected moment slab system for static load calculations System Selected MSWa (ft) Tested MSWa (ft) Barrier Shape Resistance to Rotationc (kips) Resistance to Slidingc (kips) TL-3 4.0 4.5 Vertical wall (tested) 22.6 34.7 TL4-1 4.5 5.2 Single slope (tested) 30.0 38.3 TL4-2 4.5 N/Ab Vertical wall 23.8 40.2 TL5-1 7 7 NJ profile (tested) 79.1 89.2 TL5-2 12 N/Ab Vertical wall 184.4 132.5 a MSW stands for Moment Slab Width b N/A not applicable c Resistance computed for selected MSW 9.3.4 Data for TL-3 1) Dynamic Load The design load for MASH TL-3 impacts was updated from 54 kips (240 kN) in NCHRP Report 663 to 70 kips (311 kN) recommended herein The 54 kip (240 kN) load was obtained from an impact simulation performed with a Chevrolet C2500 pickup truck model (Figure 3-1-a) that conformed to the 2000P design test vehicle in NCHRP Report 350 (4). A FE model of the 2270P pickup truck (Figure 3-1b) recommended in MASH (5) was not available at the time of the previous project. Therefore, although the 2270P vehicle was used in the TL-3 crash test, FE simulation could not be used to develop a complete understanding of the associated impact load. In the current project, the 2270P vehicle model was used to update the TL-3 impact load to correspond with MASH impact conditions (Figure 9-13). A load of 70 kips (311 kN) is considered to represent an upper bound of the lateral impact load, and consequently is the revised recommended dynamic load for MASH TL-3. 2) Previously Established Static Load The equivalent static load is revised from the previously recommended 10 kips (44.5 kN) in NCHRP Report 663 to 18 kips (80 kN). The 10 kip (44.5 kN) load represented the static resistance of the BMS system around point of rotation A in a 13 mph bogie test impact (NCHRP Report 663 (2)). This test assembly was chosen because the impact results revealed a 54 kip (240 kN) dynamic impact load associated with 1 in dynamic displacement at the top of the barrier. Since the 1 in. (25.4 mm) maximum movement was considered acceptable at the time of the first project, the BMS geometry used in the bogie test was used in the static resistance calculations. The resulting static resistance with a 4.5 ft (1.37 m) wide and 20-ft (6.10 m) long moment slab was 10 kips (44.5 kN). As a result, the 10 kips (44.5 kN) was adopted as an equivalent static load with a minimum moment slab width of 4.5 ft (1.37 m). It was stated, however, that in order to have a safety factor of 1.5, a 30 ft (9.14) moment slab should be used, which would yield a resistance to rotation of 15 kips (67 kN) about point A.
263 Figure 9-13 TL3 (3 in) Impact Load versus Time. Since the NCHRP 663 Report was published, the design practices of MSE retaining walls moved from an ASD method to a LRFD method. Also, as more knowledge was gained through research of the TL-4 and TL-5 systems, the considerations for selection of the BMS systems from which the static resistance (and consequently the equivalent static load) is calculated were revised, and additional simulation were carried out to select an adequate system. 3) BMS system The crash test of a vertical wall barrier with a moment slab width of 4.5 ft (1.37) was documented in NCHRP Report 663. The maximum dynamic displacements at the top of the barrier and at the coping level were 0.84 in and 0.37 in, respectively. The maximum permanent displacements at the top of the barrier and at the coping level were 0.55 in. (13.97 mm) and 0.25 in. (6.35 mm) respectively. No panel damage or distress was observed in the test. From a serviceability point of view (displacement criterion), the crash-tested TL3 BMS system has reserve strength and additional movement could be tolerated within the serviceable limits previously described. Two additional FE simulations were carried out for the same barrier system with narrower 4.0-ft (1.22 m) and a 3.5-ft (1.07 m) wide moment slabs. These simulations were compared to the TL-3 impact simulation of the crash-tested system with 4.5 ft (1.37 m) moment slab width. The displacement versus time curves for the top of the barrier and at the coping level are shown in Figure 9-14 and Figure 9-15, respectively. The curves correspond to the nodes at which the maximum displacements were obtained. As shown in Figure 9-14, the dynamic displacements at the top of the barrier follow the same trends for moment slab widths of 4 ft (1.22 m) and 4.5 ft (1.37 m). The maximum dynamic displacements are 1.05 in. (26.67 mm) and 0.9 in. (22.86 mm) for moment slab widths of 4 ft (1.22 m) and 4.5 ft (1.37 m), respectively. For a moment slab width of 3.5 ft (1.07 m), a significant change in the displacement is observed. The maximum dynamic displacement for a 3.5-ft (1.07 m) wide moment slab increases to 1.42 in. (36.07 mm). Figure 9-15 shows that the permanent displacement of the coping related to the three moment slab widths is about 0.7 in. (17.78 mm), which is less than the maximum criterion of 1 in. (25.4 mm). 71.4 kips
264 Figure 9-14 Maximum displacements at the top of the barrier versus time for TL-3 Impact Levels with moment slab widths 3.5, 4.0 and 4.5 ft. Figure 9-15 Maximum displacements at the coping level of the barrier versus time for TL- 3 Impact Levels with moment slab widths 3.5, 4.0 and 4.5. Based on the simulation results, the system with 4.0 ft (1.22 m) moment slab width was adopted for equivalent static load calculations. The maximum dynamic movement at the barrier top is 1 in, and the permanent displacement at the coping level of the barrier is less than the maximum value of 1 in. (25.4 mm). Hence, this system satisfies the serviceability limit states specified in Section 9.3.3. The adopted system is shown in Figure 9-16. Note that the moment slab width of 4 ft (1.22 m) is measured from the inside face of the wall panel to the end of the free end of the moment slab. -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 Di sp la ce m en t ( in ) Time (s) Maximum TL-3 Barrier Top Displacements Based on Simulations TL-3/ 3.5 ft. TL-3/ 4.0 ft. TL-3/ 4.5 ft. -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 Di sp la ce m en t ( in ) Time (s) Maximum TL-3 Barrier Coping Displacements based on Simulations TL-3 /3.5 ft. TL-3/4.0 ft. TL-3/ 4.5 ft.
265 Figure 9-16 TL-3 BMS system used in the calculation of resistance against sliding and overturning. 4) Equivalent Static Load The recommended equivalent static load for TL-3 was obtained by selecting the minimal barrier moment slab system that satisfies the selected performance criterion. The static resistance against sliding and overturning of the selected BMS system with 4-ft (1.22 m) wide moment slab (Figure 9.16) was calculated. The resistance to sliding and overturning for this system was determined to be 35 kips (156 kN) and 23 kips (102 kN), respectively. Since the overturning resistance is more critical, it was used to obtain the equivalent static load. By using equation 9.3 and a resistance factor of 1, an equivalent static load of 23 kips (102 kN) was obtained. A 4-ft (1.22 m) wide moment slab is considered to be the minimum width required for the TL-3 moment slab. The point of load application is 2 ft (0.61 m) measured from the roadway grade. 5) Wall Reinforcement a) Pullout of the Wall Reinforcement The recommendations for the wall reinforcement design pressure for TL-3 were presented in NCHRP Report 663. These design pressures were based on a dynamic load measured during the bogie crash test equal to 70 kips (311 kN). But the dynamic load obtained from the TL-3 simulation was around 54 kips (240 kN) at the time. For this purpose, the data measured from the bogie test was reduced by multiplication of the numbers obtained from the bogie test by a factor of 54/70. Since the dynamic load for MASH TL-3 has been revised herein from 54 kips (240 kN) to 70 kips
266 (311 kN) based on FE simulation using the MASH 2270P pickup truck model, the measured strip loads no longer require the interpolation of the measured values. Also, following the methodology described in Section 9.3.2, the total design load was compared to the calculated resistance to make final recommendations for the first and second reinforcement layers. The design strip load in excess of the static load in bogie test 3, that included 8 ft (2.44 m) long reinforcement strips, was used to develop the design guideline for pullout of the reinforcement. As stated in NCHRP Report 663, this test was selected because the wall performed well during that impact. The full-scale TL-3 crash test was carried out with reinforcement strip length of 10 ft (3.05 m). The maximum 50-msec. average dynamic loads were 2.21 kips (9.83 kN) for the first layer and 0.66 kips (2.94 kN) for the second layer. These measurements are used to obtain the recommended design pressures and the design line load recommendations. The previous recommendations were based on Bogie test 3 (NCHRP 663). They are updated herein using the TL-3 crash test data, similar to what is done with TL-4-1 and TL-5-1. The resistance (P) for the 10 ft (3.05 m) long strips was calculated to be 1.93 kips (8.59 kN) for the uppermost layer and 3.21 kips (14.28 kN) for the second layer (using Eq. 9-7). The friction factor (F*) used to calculate the resistance was 1.63 for the uppermost layer and 1.49 for the second layer. The maximum dynamic load (50-msec. average) was measured to be 2.21 kips (9.83 kN). The static load at the uppermost layer was calculated to be 0.60 kips (2.67 kN) by AASHTO LRFD. The total design load equals the summation of the dynamic load and static load and was calculated to be 2.81 kips (12.50 kN). The total design load of 2.81 kips (12.50 kN) was higher than the resistance of 1.93 kips (8.59 kN), thus the resistance was used to obtain the controlling dynamic design load in excess of the static load at the uppermost layer. The controlling dynamic load was calculated to be 1.33 kips (5.92 kN). This value was found by subtracting the static load due to earth pressure (0.6 kips (2.67 kN)) from the factored total resistance P (1.93 kips (8.59 kN) multiplied by a factor of 1). This load represents a static load, equivalent to a dynamic impact load, which reflects that the 10 ft (3.05 m) long strip performed well in a MASH TL-3 impact. The static load for the second layer was calculated to be 1.16 kips (5.20 kN) by AASHTO LRFD. A total load of 1.82 kips (8.10 kN) was obtained by adding the measured dynamic load of 0.66 kips (2.94 kN) to the static load. Since the calculated resistance of 3.21 kips (14.28 kN) was more than the total load, the measured dynamic load of 0.66 kips (2.94 kN) was used as the controlling dynamic load for pullout design. Table 9-8 presents the total load, the calculated static load, the measured dynamic load, the calculated pullout resistance, and the controlling dynamic design load as described.
267 Table 9-8 Simulation results and calculation of TL-3 design strip load for pullout (1) Total Load (kips) (2) Static Load (kips) (3) Dynamic Load (kips) (4) Calculated Resistance (a) (kips) Controlling Design Dynamic Load (kips) Dynamic Design Pressure P (psf) Top Layer 2.81 0.60 2.21 1.93 (4)-(2) = 1.33 1330 kips / 3.62 ft2 (b)= 368 psf (final 370 psf) Second Layer 1.82 1.16 0.66 3.21 (3) =0.66 1660 kips / 3.99 ft2 (c)= 165 psf (final 165 psf) (a) Calculated from AASHTO 11.10.6.2 â 11.10.6.3 (b) Tributary area of the panel for the top layer (3.62 ft2 = 4.87 ft à 2.23 ft / 3 strips per panel) (c) Tributary area of a panel for the second layer (3.99 ft2 = 4.87 ft 2.46 ft / 3 strips per panel) The dynamic pressure per strip was calculated as shown in Table 9-8. For the 10 ft (3.05 m) long strip with a density of six strips per panel, the tributary area was 3.62 ft2 (0.34 m2) for the top layer and 3.99 ft2 (0.37 m2) for the second layer. Total design pressures of 368 psf (17.62 kPa) and 165 psf (7.90 kPa) were calculated for the top and second layer of reinforcement, respectively, by dividing the controlling dynamic load by the corresponding tributary area for each strip. Thus, the recommended pullout dynamic design pressure in excess of the static earth pressure is 370 psf (17.72 kPa) for the upper most layer and 165 psf (7.9 kPa) for the second layer (the calculated value for the upper layer is rounded for simplification). To calculate the corresponding line load, the recommended pressures of 370 psf (17.72 kPa) for the first layer and the 165 psf (7.9 kPa) for the second layer were multiplied by the tributary height of 2.25 ft (0.68 m) and 2.5 ft (0.75 m), respectively (see Table 9-4). The calculated value is 832.5 lb./ft (12.15 kN/m) for the first layer and 412.5 lb./ft (6.02 kN/m) for the second layer. For simplification, a value of 835 lb./ft was adopted for the first layer and 415 lb./ft was adopted for the second layer as shown in Table 9-3. b) Yielding of the Wall Reinforcement The reinforcement resistance to yielding (R) for a strip was calculated to be 13.05 kips (58 kN) using Eq. (9-15) for 75 years of service life. To develop the design guideline against yielding of the reinforcement, the highest dynamic load on the strip obtained from the bogie tests and TL-3 crash test were used. The maximum 50-msec. average dynamic load on the strip located in the uppermost layer was 7.23 kips (kN) from Bogie Test 1 with 16 ft (4.88 m) long strips. In the second layer, the maximum measured 50-msec. average dynamic load was 1.19 kips (kN) from Bogie Test 3 with 8 ft (2.44 m) long strips. The dynamic pressure per strip for yielding of the reinforcement was calculated as shown in Table 9-9. The selected loads (dynamic design loads) were divided by the corresponding tributary area to obtain dynamic design pressure pd of 1414.87 psf (67.74 kPa) and 298.25 psf (14.28 kPa) for the upper and lower reinforcement layers, respectively. The recommended pressures, presented in Table 9-4, are 1415 psf (67.75 kPa) for the uppermost layer and 300 psf (14.36 kPa) for the second layer (i.e., the calculated values rounded to the nearest ten).
268 Table 9-9 TL-3 design pressure for yielding of soil reinforcement based on bogie test results Layer Total Design Load (kips) Static Load (kips) Dynamic Design Load (kips) Dynamic Design Pressure, pd Top 7.92 0.69 7.23 7230 lb. / 5.11 ft2(a)= 1414.87 psf (final 1415 psf) Second 2.44 1.07 1.19 1190 lb./3.99 ft2(b)= 298.25 psf (final 300 psf) (a) Tributary area of the panel for the top layer (5.11 ft2 = 4.87 ft à 2.1 ft / 2 strips per panel) (b) Tributary area of a panel for the second layer (3.99 ft2 = 4.87 ft à 2.46 ft / 3 strips per panel) To determine the line loads, the pressures of 1415 psf (67.75 kPa) and 300 psf (14.36 kPa) obtained for the uppermost and second layer of reinforcement were each multiplied by the corresponding heights of 2.25 ft (0.67 m) and 2.5 ft (0.76 m), respectively. This resulted in line loads of 3183.75 lb./ft (46.46 kN/m) for the first layer, and 750 lb./ft (10.95 kN/m) for the second layer. Simplified values of 3185 lb/ft and 750lb/ft are recommended for the first and the second layers respectively. c) Reinforcement of the wall panel The reinforcement of the wall panel should be able to resist the bending moment created on the panel by the friction force between the bottom of the barrier and the top of the panel (or top of leveling pad). This bending moment should be calculated as the weight of the barrier plus the overburden soil times the coefficient of friction at that interface. 9.3.5 Data for TL-4-1 and TL-4-2 The TL-4 recommendations for the dynamic impact load were divided into two design cases: the TL-4-1 case for a barrier height of 36 in. (0.91 m), and the TL-4-2 case for a barrier height of 42 in. (1.07 m) as measured from the roadway grade level. In the TL4-1 case, the floor of the box of the truck does not make contact with the barrier during the initial impact. This results in less contact area between the truck and the barrier, and consequently more vehicle roll in comparison with the TL-4-2. As a result, the TL-4-1 and the TL-4-2 have different dynamic loads. As will be seen later, the difference in dynamic load between the two TL-4 cases is relatively small (12.5%) compared to the one between the TL-5-1 and TL5-2 cases. As such the barrier displacements for the TL-4-1 and the TL-4-2 are comparable. A discussion of the barrier displacements of both systems is presented below. Since the TL-4-2 has a slightly higher dynamic load, the TL-4-2 strip load data was used for the recommendations of both the TL-4-1 and TL-4- 2 load cases.
269 1) Dynamic Load TL-4-1 The MASH TL-4-1 impact case relates to a barrier height of 36 in. (0.91 m). The design impact load for MASH TL-4-1 is 70 kips (311 kN). The 70 kips is rounded from a peak load of 67.2 kips shown in Figure 9-17, considering that 70 kips is also the recommended dynamic load for TL-3. This load was selected with consideration to both theoretical and experimental data analyses, and is considered to be representative of the upper bound lateral impact load imposed by the MASH TL-4-1 test vehicle. For stability of the MASH 10000S test vehicle, the minimum recommended barrier height is 36 in. (0.91 m). This barrier height was successfully crash tested under MASH TLL-4 impact conditions by TTI researchers (19). Figure 9-17 TL-4-1 Impact Load versus Time for 36 in. (0.91 m) barrier. 2) Dynamic Load TL-4-2 The selected design load for MASH TL-4-2 is 80 kips (356 kN). The 80 kips is rounded from a peak load of 79.1 kips shown in Figure 9-18. This load was selected after considering both theoretical and experimental data analyses, and it represents the upper bound lateral impact load imposed by the MASH TL-4 test vehicle for a barrier taller than 36 in. (0.91 m). 67.2
270 Figure 9-18 TL4-2 Impact Load versus Time for 42 in. (1.07 m) barrier. 3) Barrier-Moment Slab System for TL-4-1 A decision was made to aim for a TL-4 BMS system that would generate about 1.5 in. (38.1 mm) dynamic displacement at the barrier top and 1 in. (25.4 mm) permanent displacement at the coping section. The dynamic displacement limit accounts for the additional barrier height beyond the TL- 3 barrier height and results in acceptable performance in FE impact simulations. The permanent movement is selected to provide a design that requires little or no repair of the underlying MSE wall. A TL-4-1 barrier with a moment slab width of 5.2 ft (1.58 m) was crash tested. The maximum dynamic displacements at the top and at the bottom of the barrier were about 0.5 in and 0.4 in respectively. The maximum permanent displacements at the top and the bottom of the barrier were 0.2 in. (5.08 mm) and 0.31 in. (7.87 mm) respectively. No panel damage was recorded as a result of the impact. From a serviceability point of view, it is likely that the TL-4-1 crash-tested BMS system has significant reserve strength and additional movements could be tolerated within the serviceable limits, i.e., without panel damage and without compromising impact performance. To study this issue, two additional FE simulations were carried out for the same TL-4 barrier system with smaller moment slab widths of 4.5 ft (1.37 m) and 4.0 ft (1.22 m). These simulations were compared with the displacements in the simulation of the crash-tested system, with a moment slab width of 5.2 ft (1.58 m). The displacement versus time curves at the top of the barrier and at the coping levels are shown in Figure 9-19 and Figure 9-20, respectively. These displacements correspond to the nodes where maximum movement took place. 79.1
271 Figure 9-19 Maximum displacements at the top of the barrier versus time for TL-4-1 Impact Levels with moment slab widths 4.0, 4.5 and 5.2 ft. Figure 9-20 Maximum displacements at the coping level of the barrier versus time for TL- 4-1 Impact Levels with moment slab widths 4.0, 4.5 and 5.2 ft. The system with a 4.0 ft (1.22 m) moment slab moved more than 2 in. (50.8 mm) dynamically (Figure 9-19). Although the SUT was successfully contained and redirected, this movement is considered too large with respect to the serviceability limit states. In comparison, the maximum displacement at the top of the barrier for the TL-5-1 test was 1.54 in. (39.12 mm) based on FE simulation results. Also, based on Figure 9-19, the system with a 4.0 ft (1.22 m) moment slab shows a significant increase in the displacement behavior compared to the other widths (4.5 -0.5 0 0.5 1 1.5 2 2.5 0 0.1 0.2 0.3 0.4 0.5 0.6 Di sp la ce m en t ( in ) Time (s) Maximum Barrier Top Displacements Based on Simulations TL4-1/ 4 ft. TL4-1/ 4.5 ft. TL4-1/ 5.2 ft. -0.2 0 0.2 0.4 0.6 0.8 1 1.2 0 0.1 0.2 0.3 0.4 0.5 0.6 Di sp la ce m en t ( in ) Time (s) Maximum Barrier Coping Displacements Based on Simulations TL4-1/ 4 ft. TL4-1/ 4.5 ft. TL4-1/ 5.2 ft.
272 ft (1.37 m) and 5.2 ft (1.58 m)). As explained before, the tested system had a moment slab width of 5.2 ft (1.58 m), which was shown to be conservative. The system with a moment slab width of 4.5 ft (1.37 m) exhibit slightly larger, yet similar displacement trends as that of 5.2 ft (1.58 m) moment slab system. The maximum dynamic and permanent displacements of this system are 1.5 in. (38.1 mm) at the top of the barrier and 0.79 in. (20.07 mm) at the coping level respectively. The analysis indicated that a 4.5-ft (1.37-m) wide moment slab meets the chosen dynamic displacement criterion of 1.5 in. (38 mm) at the barrier top and the permanent displacement criterion of 1 in. (25.4 mm) at the coping level of the barrier. As a result, a 4.5-ft (1.37 m) wide moment slab system was adopted for TL-4-1. 4) Barrier-Moment Slab System for TL-4-2 The results of a TL-4-2 simulation for a BMS system with a vertical wall barrier and a 4.5-ft (1.37 m) wide moment slab were compared with the results of the selected TL-4-1 system which also had a 4.5-ft (1.37 m) wide moment slab. The results are shown as a function of time in Figure 9- 21 and Figure 9-22 for the top barrier dynamic displacements and the bottom barrier dynamic displacements, respectively. Figure 9-21 shows that the TL-4-2 displacements are similar to those of the TL-4-1 case with a maximum barrier top displacement of 1.5 in. (38.1 mm). At the coping level, the permanent displacements are also comparable. For this reason, this system was selected for the calculation of the equivalent static load. Figure 9-21 Maximum displacements at the top level of the barrier versus time for TL-4-1 and TL-4-2 Impact Levels with 4.5 ft moment slab width. 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 0 0.1 0.2 0.3 0.4 0.5 0.6 Di sp la ce m en t ( in ) Time (s) Maximum Barrier Top Displacements Based on Simulations TL4-1/ 4.5 ft. TL4-2/ 4.5 ft.
273 Figure 9-22 Maximum displacements at the coping level of the barrier versus time for TL- 4-1 and TL-4-2 Impact Levels with 4.5 ft moment slab width. 5) Equivalent Static Load for TL-4-1 The recommended equivalent static load for TL-4-1 was obtained by considering the static resistance against overturning of the selected BMS system with a 4.5-ft (1.37 m) wide moment slab (Figure 9-23). The resistance to sliding for this system is 38 kips (169 kN) and the resistance to overturning is about 28 kips (125 kN).Since the resistance to overturning is more critical, it was used to obtain the equivalent static load. By using equation 9-3, an equivalent static overturning load of 28 kips (125 kN) is calculated and this value is recommended as the equivalent static overturning load. Figure 9-23 TL-4-1 BMS system used in the calculation of resistance against sliding and overturning. -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 0.1 0.2 0.3 0.4 0.5 0.6 Di sp la ce m en t ( in ) Time (s) Maximum Barrier Coping Displacements Based on Simulations TL4-1/ 4.5 ft. TL4-2/ 4.5 ft.
274 The 4.5-ft (1.37 m) wide moment slab was considered as the minimum required moment slab width for TL-4-1. The point of application of the load is approximately 25 in. (0.64 m), measured from the roadway grade (see Figure 9-23). The calculation indicates that a 36-in. (0.91-m) tall barrier mounted to a 4.5-ft (1.37 m) wide (measured from the inside face of the panel), 30-ft (9.14-m) long moment slab, without considering the contribution of the surrounding soil at the interface area between the BMS system and the soil, is capable of withstanding a TL-4-1 impact. 6) Equivalent Static Load for TL-4-2 The recommended equivalent static load for the case of the TL-4-2 impact was obtained by considering the static resistance against overturning of the selected BMS system with 4.5 ft (1.37 m) moment slab width (Figure 9-24). The resistance to sliding for this system is around 40 kips (178 kN), and the resistance to overturning is around 24 kips (106.76 kN). Hence the resistance to overturning is the most critical, and is used in the calculations of the equivalent static load. This overturning resistance is less than the 28 kips (125 kN) calculated for TL-4-1. This is attributed to the difference in the barrier shape (a single-slope barrier was analyzed for TL-4-1 and a vertical wall barrier was simulated for TL-4-2). This results in a change in the CG of the BMS system that, in turn, is involved in the calculations of the resistance to rotation. Figure 9-24 TL-4-2 BMS system used in the calculation of resistance against sliding and overturning. To simplify the recommendations, a 28 kips (125 kN) is recommended as an equivalent static overturning load for both TL-4-1 and TL-4-2. Another consideration is that the dynamic loads are comparable (70 kips (311.38 kN) and 80 kips (355.86 kN) for TL-4-1 and TL-4-2 respectively), and the barrier shape affects the calculations of the resistance to overturning.
275 A 4.5-ft (1.37-m) wide moment slab was considered as the minimum width required for the moment slab for TL-4-2. The point of application of the load is 30 in. (0.76 m), measured from the roadway grade. In summary, it was concluded that a 42-in. (1.07 m) tall barrier mounted to a 4.5-ft (1.37 m) wide (measured from the face of the panel), 30-ft (9.14-m) long moment slab can withstand a TL-4-2 (and a TL-4-1) impact, without considering the contribution of the surrounding soil at the interface area between the BMS system and the soil. 7) Wall Reinforcement The results of the TL-4-1 full-scale crash test, the full-scale TL-4-1 impact simulations and the TL-4-2 impact simulations with reinforcement lengths of 10 ft (3.05 m), 16 ft (4.88 m) and 24 ft (7.32 m) were evaluated to develop the guidelines for wall reinforcement for MASH TL-4 impacts. The simulation results showed that the dynamic impact load on the barrier for TL-4-2 was slightly higher than that for TL-4-1, with values of 80 kips (355.9 kN) versus 70 kips (311.4 kN). Thus, the TL-4-2 system with a 4.5-ft (1.37 m) wide moment slab was used to obtain the reinforcement loads for both systems. Little movement was observed in the TL-4-1 crash test. The reason is that the system included a moment slab width of 5.2 ft (1.58 m), which provided a conservative static resistance. As a result, the forces measured in the strips were less than those obtained from the simulations for the less conservative moment slab system that was adopted as a minimum for TL-4-1. Consequently, researchers relied on simulation data when developing the guidelines for TL-4 wall reinforcement. The maximum 50-msec. average total loads, dynamic loads, and the wall displacement measured during the impact simulation are summarized in Table 9-10. The loads presented in Table 9-10 were obtained at 7 in. (178 mm) from the face of the wall where the dynamic load is expected to be the highest. Even though the reinforcement appears to have reached its maximum pullout resistance during impact simulation, the overall performance of the wall was satisfactory in the FE analysis. Therefore, it was decided that having the reinforcement working at maximum pullout resistance would be acceptable given that the load duration is so short and the resulting displacements were tolerable. The design recommendations are based on a pressure diagram approach that prescribes the pressure due to impact (in excess of static load) that must be resisted by the reinforcement. a) Pullout of the Wall Reinforcement The average design strip load in excess of static for the TL-4 impact simulation with 10 ft (3.05 m) long reinforcing strips was used to develop the design guidelines for pullout of the reinforcement. This reinforcement length was selected for pullout analysis as it generated the largest wall displacement.
276 Table 9-10 Summary of the pullout resistance, maximum 50-msec. average strip load and wall displacement for MASH TL-4 impact simulation. Strip Length (ft) AASHTO Pullout Resistance * (kips) Total Strip Load (kips) Dynamic Wall Displacement (in) Approximate Permanent Wall Displacement (in) First Layer Second Layer First Layer Second Layer Top (1) First Layer Second Layer Top (1) First Layer Seco nd Layer 10 1.95 3.23 4.4 2.24 0.37 0.20 0.07 0.13 0.07 0.02 16 3.12 5.17 5.8 1.9 0.29 0.16 0.04 0.08 0.04 0.02 24 4.67 7.75 7.0 1.7 0.22 0.12 0.02 0.04 0.03 0.03 (1) Displacement measured at the coping level (2) *AASHTO mention Cu=D60/D10=4 The resistance (R) for the 10 ft (3.05 m) long strips was calculated to be 1.95 kips (8.67 kN) for the upper most layer and 3.23 kips (14.37kN) for the second layer using Eq. (2-2) in Chapter 2 (AASHTO 11.10.6.3.2-1). A pullout friction factor F* of 1.63 was used for the uppermost layer, and a factor of 1.49 was used for the second layer. The total load (50-msec. average) in the strips within the upper most layer was 4.4 kips (19.6 kN) as shown in Table 9-10. Although the measured total load in the strip was higher than the resistance (1.95 kips (8.67 kN)), the displacement of the strips and the performance of the wall were considered acceptable. In other words, the analyses indicate that an MSE wall with 10 ft (3.05 m) long strip will perform acceptably in a TL-4 impact. The resistance was used to obtain the controlling dynamic design load in excess of the static load at the upper most layers. The load was calculated to be 1.34 kips (5.96 kN) by subtracting the static load of 0.61 kips (2.71 kN) from the factored resistance (1.95 kips (8.67 kN) multiplied by a factor of 1) For the second layer, the total simulated load was found to be 2.24 kips (10 kN). The static earth pressure load for the second layer was calculated to be 1.16 kips (5.16 kN) by AASHTO LRFD. The total load from the simulation (2.24 kips (10 kN) was less than the calculated pullout resistance of 3.23 kips (14.37 kN) at that depth. Therefore, the measured dynamic load of 1.08 kips (4.80 kN), obtained by subtracting the static load from the total load, was used as the controlling dynamic load for pullout design for that layer. Table 9-11 presents a summary of the total loads, the calculated static loads, the dynamic loads measured from the simulation, the calculated pullout resistance, and the recommended design pressure for pullout resistance. The dynamic pressure per strip (Table 9-11) was calculated using the tributary areas as follows. For the 10 ft (3.05 m) long strip with a density of three strips per panel per layer, the tributary area was 3.64 ft2 (0.34 m2) for the top layer and 3.99 ft2 (0.37 m2) for the second layer. The dynamic design pressure in excess of the static earth pressure for pullout was calculated to be
277 368.68 psf (17.65 kPa) for the first layer and 269.67 psf (12.91 kPa) for the second layer. To simplify the recommendations, the calculated number was rounded to 370 psf (17.7 kPa) for the upper most layer and 270 psf (12.93 kPa) for the second layer. Table 9-11 Simulation results and calculation of TL-4 design strip load for pullout. (1) Total Load (kips) (2) Static Load (kips) (3) Dynamic Load (kips) (4) Calculated Resistance (a) (kips) Controlling Dynamic Design Load (kips) Dynamic Design Pressure pd (psf) Top Layer 4.4 0.61 3.79 1.95 (4)-(2) = 1.34 1340 kips / 3.64 ft2 (b) = 368.8 psf (final 370 psf) Second Layer 2.24 1.16 1.08 3.23 (1)-(2) = 1.08 1080 kips / 3.99 ft2 (c) = 269.67 psf (final 270 psf) (a) Calculated from AASHTO 11.10.6.2 â 11.10.6.3, assuming Cu=D60.D10=4 (b) Tributary area of the panel for the top layer (3.64 ft2 = 4.87 ft à 2.24 ft / 3 strips per panel) (c) Tributary area of a panel for the second layer (3.99 ft2 = 4.87 ft à 2.46 ft / 3 strips per panel) To calculate the corresponding line load, the recommended pressures of 370 psf (17.7 kPa) for the first layer and the 270 psf (12.93 kPa) for the second layer were multiplied by the tributary height of 2.25 ft (0.68 m) and 2.5 ft (0.76 m), respectively (shown in Table 9-2). The calculated value is 832.5 lb./ft (12.15 kN/m) for the first layer and 675 lb./ft (9.85 kN/m) for the second layer. For simplification, a value of 835 lb./ft was adopted for the first layer and 675 lb./ft was selected for the second layer as shown in Table 9-3. b) Yielding of the Wall Reinforcement The reinforcement resistance to yielding (R) for a strip was calculated using Eq. (9-15). The tensile strength of the reinforcement (Ït) was 65 ksi (448 MPa) and the thickness, after accounting for corrosion loss (Ec), was 0.102 in. (2.59 mm) for a 75-year design life. The value of R was computed to be 13.05 kips (58 kN). To develop the design guidelines against yielding of the reinforcement, the highest design load on the strip, computed from the full-scale impact simulation, was used. The maximum 50-msec. average total load on the strip located in the uppermost layer was 7 kips (31.2 kN) (24 ft (7.32 m) long strip) as shown in Table 9.10. In the second layer, the total load was 2.24 kips (10 kN) and 1.9 kips (8.5 kN) for the simulations with 10 ft (3.05 m) and 16 ft long reinforcing strips, respectively. Therefore, the controlling dynamic design strip load for yielding of the reinforcement is 6.39 kips (28.42 kN) for the uppermost layer and 1.08 kips (4.80 kN) for the second layer, respectively, as shown in Table 9-12.
278 Table 9-12 Simulation results for TL-4 impact and calculation of design strip load for yielding design. Strip Length (ft) (1) Dynamic Load (kips) (2) Static Load(a) (kips) (3)= (1)+(2) Total Load (kips) (4) Calculated Resistance(b) (kips) Controlling Design Dynamic Load for all cases (kips) First Layer Second Layer First Layer Second Layer First Layer Second Layer First Layer Second Layer First Layer Second Layer 10 3.79 1.08 0.61 1.16 4.4 2.24 13.05 13.05 6.39 16 5.19 0.74 0.61 1.16 5.8 1.9 13.05 13.05 1.08 24 6.39 0.54 0.61 1.16 7.0 1.7 13.05 13.05 (a) Calculated from AASHTO 11.10.6.4.3 (b) Reinforcement steel ASTM Grade 60 The dynamic pressure per strip for yielding of the reinforcement was calculated as shown in Table 9-13. For the 10 ft (3.05) long strip with a density of three strips per panel per layer, the tributary area was 3.99 ft2 (0.37 m2). For the 24 ft (7.32 m) long strip with a density of two strips per panel per layer, the tributary area was 3.64 ft2 (0.34 m2). For the first layer, the controlling dynamic design load of 6.39 kips (28.42 kN) was divided by the tributary area of 3.64 ft2 (0.34 m2), and a dynamic design pressure of 1755.49 psf (84 kPa) was obtained. For the second layer, a design pressure of 270.68 psf (12.96 kPa) was obtained by dividing controlling dynamic design load of 1.08 kips (4.80 kN) by the tributary area of 3.99 ft2 (0.37 m2). To simplify the guidelines, the recommended pressures were rounded to 1755 psf (84 kPa) and 300 psf ( 14.36 kPa) for the first and second layer respectively. This way, the recommended values for the second-layer strip for TL-4 will match those for TL-3. The reason is that, as explained before, the dynamic loads for TL- 3, TL-4-1 and TL-4-2 are comparable (70 kips, 70 kips and 80 kips respectively). To calculate the corresponding line load, the recommended pressures of 1755 psf (84 kPa) for the first layer and the 270 psf (12.93 kPa) for the second layer were multiplied by the tributary heights of 2.25 ft (0.68 m) and 2.5 ft (0.76 m), respectively (shown in Table 9-4). The calculated values are 3948.75 lb./ft (57.63 kN/m) for the first layer, and 675 lb./ft (9.8 kN/m) for the second layer. For simplification, values of 3950 lb/ft and 750 lb/ft were chosen.
279 Table 9-13 TL-4 design pressure for yielding of soil reinforcement based on simulation results. Layer Total Design Load (kips) Static Load (kips) Dynamic Design Load (kips) Dynamic Design Pressure, pd Top 7.0 0.61 6.39 6390 lb./ 3.64 ft2 (a) = 1755.49 psf (final 1755 psf) Second 2.24 1.16 1.08 1080 lb./3.99 ft2 (b) = 270.68 psf (final 300 psf) (a) Tributary area of the panel for the top layer (3.64 ft2 = 4.87 ft à 2.24 ft / 3 strips per panel) (b) Tributary area of a panel for the second layer (3.99 ft2 = 4.87 ft à 2.46 ft / 3 strips per panel) 9.3.6 Data for TL-5-1 1) Dynamic Load The final design impact load for MASH TL-5-1 impact is 160 kips (712 kN) (Figure 9-25). This load was selected by using the results of the FE analyses described in Chapter 3. The load is considered to be representative of the upper bound lateral impact load imposed by the MASH 36000V test vehicle for a 42 in. (1.07 m) barrier height. It also includes the component of friction generated at the top of the barrier due to the vehicle riding on top of it while it is being redirected. A minimum barrier height of 42 in. (1.07 m) is required for stability of the MASH 36000V test vehicle. This barrier height has been successfully crash tested as shown in Table 2-4. Figure 9-25 TL5-1 (42 in) Impact Load versus Time. 159 kips
280 One of the recommendations made to preclude damage to the underlying MSE wall or significant relative displacement between barriers is that the length of the precast barrier section for TL-5-1 be at least 15 ft (4.57 m). This length will enable the barriers to develop the complete failure mechanism (yield line) in the barrier face provided the coping is sufficiently strong. The goal is to ensure that the barrier fails before any other part of the system because it reduces the cost of repair after a severe impact. 2) Barrier-Moment Slab System The TL-5-1 crash test involved a NJ barrier that was 42 in. (1.07 m) in height (measured from the roadway grade) and a 7.15-ft (2.18 m) wide moment slab. The barrier system performed satisfactorily with a maximum permanent displacement of 1.06 in and 0.44 in at the top and bottom of the barrier, respectively (Table 9.6). Hairline cracks were observed in two of the panels, which is the reason why the static resistance of the tested system to sliding and overturning was considered the minimum recommended resistance. The TL-5-1 FE simulation termed TL5- 1/NJ/7.15ft is representative of the TL-5-1 crash test installation. Figure 9-26 and Figure 9-27 show a comparison of the maximum displacement versus time curve at the barrier top and coping levels, respectively, for a vertical wall barrier and the NJ barrier system. The simulation predicted a permanent movement of 0.8 in. (20.32 mm) and 0.6 in. (15.24 mm) at the top of the barrier and at the coping sections of the NJ barrier, respectively. These results are comparable to the 1.06 in. (26.92 mm) and 0.48 in. (12.19 mm) displacements obtained at the barrier top and barrier coping in the actual crash test (Table 9-6). Figure 9-26 Maximum Displacements obtained at the top of a barrier of TL5-1 tested NJ Barrier and a straight barrier versus Time. -0.5 0 0.5 1 1.5 2 2.5 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 Di sp la ce m en t ( in ) Time (s) Maximum Barrier Top Displacements TL5-1 Based on Simulations TL5-1/ Straight/7 ft. TL5-1/ NJ /7.15 ft.
281 Figure 9-27 Maximum Displacements obtained at the coping level of a barrier of TL5-1 tested NJ Barrier and a straight barrier versus Time. The dynamic movements of the barrier system could not be obtained from the crash test due to a camera trigger malfunction. However, the simulation results of the crash test (TL5-1/NJ 7.1ft) shown in Figure 9-26 reveal a predicted maximum dynamic movement of 1.54 in. (39.1 mm) at the barrier top. A similar simulation with a vertical wall barrier predicts a movement of about 2.13 in. (54.1mm). The vertical wall barrier exhibited dynamic movement slightly higher than that for the NJ barrier because the latter had slightly more static resistance to sliding and rotation. Since it performed well without damage that required major repairs, the crash-tested system with 7.15 ft (2.18 m) moment slab width and NJ barrier profile was used to calculate the equivalent static design loads. 3) Equivalent Static Load The recommended equivalent static load for TL-5-1 was obtained by considering the static resistance against sliding and against overturning of the crash-tested BMS system with the 7.15 ft (2.18 m) moment slab width (Figure 9-28). The resistance to sliding for this system is 89 kips (396 kN) and the resistance to overturning is 80 kips (356 kN). Since the resistance to overturning is the most critical, it was used in the calculation of the equivalent static load. By using equation 9.3, an equivalent static overturning load of 80 kips (356 kN) is obtained. The point of application of the load is 34 in. (864 mm) measured from the roadway grade. In summary, the researchers concluded that a 42-in. (1.07 m) tall barrier mounted to a 7-ft (2.13-m) wide (measured from the face of the panel), 30-ft (9.14-m) long moment slab is capable of withstanding a TL-5-1 impact while meeting the chosen displacement criteria, without considering the contribution of the surrounding soil at the interface area between the BMS system and the soil. -0.2 0 0.2 0.4 0.6 0.8 1 1.2 0 0.5 1 1.5 Di sp la ce m en t ( in ) Time (s) Maximum Barrier Coping Displacements Based on Simulations TL5-1/ NJ /7 ft. TL5-1/ Straight/7 ft.
282 Figure 9-28 BMS system used in the calculation of resistance against sliding and overturning. 4) Wall Reinforcement The results of the MASH TL-5 full-scale crash test with 10 ft (3.05 m) strip length, and the full- scale impact simulations with strip lengths of 10 ft (3.05 m), 16 ft (4.88 m), and 24 ft (7.32 m) were used to develop the guidelines for a MASH TL-5-1 impact. The simulation results showed that the impact load for this case was 167.3 kips (744.5 kN). The maximum 50-msec. average strip loads during the impact, including the total load and the dynamic component of the total load, are given in Table 9-14. Additionally, dynamic and permanent wall displacements are provided. The reinforcement strip loads presented in Table 9-14 are based on simulation results and were computed at 7 in. (178 mm) from the face of the wall panel, where the load is expected to be the highest. Even though the reinforcement appears to have reached its maximum pullout resistance during the impact, the overall performance of the wall was satisfactory in the FE impact simulation. Therefore, it was decided that having the reinforcement working at maximum pullout resistance would be acceptable given that the load duration is so short and the displacements were tolerable. The design recommendations are based on a pressure diagram approach that prescribes the pressure due to impact (in excess of static load) that must be resisted by the reinforcement.
283 Table 9-14 Summary of the pullout resistance, maximum 50-msec. average strip load and wall displacement for MASH TL-5-1 impact simulation. Strip Length (ft) AASHTO Pullout Resistance* (kips) Total Strip Load (kips) Dynamic Wall Displacement (in) Approximate Permanent Wall Displacement (in) First Layer Second Layer First Layer Second Layer Top (1) First Layer Second Layer Top (1) First Layer Second Layer 10 2.28 3.50 5.50 2.95 0.50 0.24 0.11 0.28 0.12 0.04 16 3.66 5.60 8.50 3.21 0.38 0.22 0.10 0.24 0.12 0.02 24 5.48 8.40 9.46 3.47 0.23 0.20 0.09 0.02 0.02 0.02 (1) Displacement measured at the coping level (2) Assuming Cu=D60/D10=4 as prescribed by AASHTO The results of the MASH TL-5-1 full-scale crash test are summarized in Table 9-15. The total measured loads in the first and second layer of soil reinforcement were 2.39 kips (10.64 kN) and 2.88 kips (12.82 kN), respectively. The maximum permanent displacement at the wall panels was 0.54 in. (13.7 mm). Table 9-15 Summary of the dynamic design load on the strips for pullout resistance from the MASH TL-5-1 full-scale impact test. Strip Length (ft) AASHTO Pullout Resistance* (kips) Total Strip Load (kips) Static(1) Load (kips) Dynamic(1) Load (kips) First Layer Second Layer First Layer Second Layer Top Layer Second Layer Top Layer Second Layer 10 2.28 3.50 2.40 2.88 0.79 0.90 1.60 1.98 (1) Measured loads (2) Assuming Cu=D60/D10=4 as prescribed by AASHTO a) Pullout of the Wall Reinforcement The results of the TL-5-1 full-scale test were used to develop the design guidelines for pullout of the reinforcement. The 10 ft (3.05 m) long reinforcement was selected for the test as it generated the largest displacement while having successful impact performance and meeting the overall displacement criterion. The resistance (P) for one 10 ft (3.05 m) long strip was calculated to be 2.28 kips (10.14 kN) for the upper most layer and 3.50 kips (15.57 kN) for the second layer using Eq. (2-2) in Chapter 2 (AASHTO 11.10.6.3.2-1). The pullout friction factor F* used was 1.60 for the upper most layer and 1.46 for the second layer. The maximum dynamic strip load was considered selected from the crash test and simulations.
284 Based on crash test data, the maximum measured load (50-msec. average) was 1.901 kips (8.46 kN), and the total load (50-msec. average) at the uppermost strip was 2.39 kips (10.63 kN). This load is greater than the calculated resistance of 2.28 kips (10.14 kN). So the resistance was used to obtain the controlling dynamic load. A load of 1.791 kips (7.97 kN) was calculated by subtracting the static load from the resistance. This value was divided by the tributary area to obtain the total design pressure of 725.1 psf (34.72 kPa) shown in Table 9-16. Table 9-16 Test results of the TL-5-1 impact and calculation of design strip load for pullout design (1) Total (kips) (2) Static Load (kips)(a) (3)=(1)-(2) Dynamic Load (kips) (4) Calculated Resistance(a) (kips) Controlling Dynamic Design Load (kips) Total Design Pressure (psf) Top Layer (Crash Test) 2.39 0.49 1.90 2.28 (4)-(2) = 1.79 1791 lb./2.47 ft2 (c) = 725.10 psf (Final 725) Second Layer 2.88 1.28 1.60 3.5 (1)-(2) = 1.602 1602lb./3.99 ft2 (d) = 401.5 psf (Final 400) (a) From Table 7-7 (b) Calculated from AASHTO 11.10.6.2 â 11.10.6.3, assuming Cu=D60/D10=4 as prescribed by AASHTO (c) Tributary area of the panel for the top layer (2.57 ft2 = 4.87 ft à 1.583 ft / 3 strips per panel) (d) Tributary area of a panel for the second layer (3.94 ft2 = 4.87 ft à 2.43 ft / 3 strips per panel) For the second layer, the same process was followed. The total measured dynamic load was 2.88 kips (12.81 kN). The static earth pressure load for the second layer was calculated to be 1.28 kips (5.69 kN) by AASHTO LRFD. Since the total measured load from the test (2.88 kips (12.81 kN)) was less than the calculated pullout load at that depth (3.50 kips (15.57 kN)), the measured dynamic load in excess of the static load was used as the controlling dynamic load for pullout design. Table 9-16 shows the total load, the calculated static load, the measured dynamic load from the crash test, the calculated pullout resistance, the selected controlling dynamic design load, and the recommended design pressure for pullout resistance. The dynamic pressure per strip was calculated as shown in Table 9-16. For the 10 ft (3.05 m) long strip with a density of three strips per panel per layer, with a tributary area was 2.47 ft2 (0.23 m2) for the top layer and 3.99ft2 (0.37 m2) for the second layer. The total design pressure was calculated by dividing the controlling dynamic load by the corresponding tributary area for the first and second strip layers. The resulting values were 725.1 psf 34.72 kPa) and 401.5 psf (19.22 kPa) for the first and second strip layers, respectively. Design values of 725 psf (34.71 kPa) and 400 psf were selected for simplification of the recommendations.
285 To calculate the corresponding line load, the recommended pressures of 725 psf (34.71 kPa) for the first layer and the 400 psf (19.15 kPa) for the second layer were multiplied by the tributary heights of 1.6 ft (0.48 m) and 2.5 ft (0.76 m), respectively (shown in Table 9-4). The calculated values are 1160 lb./ft (16.93 kN/m) for the first layer, and 1000 lb./ft (14.59 kN/m) for the second layer. b) Yielding of the Wall Reinforcement The reinforcement resistance to yielding (R) for a strip was calculated using Eq. (9-15). The tensile strength of the reinforcement (Ït) was 65 ksi (448 MPa) and the thickness, after accounting for corrosion loss (Ec), was 0.102 in. (2.59 mm) for a 75-year design life. The R was computed to be 13.05 kips (58 kN). To develop the design guideline against yielding of the reinforcement, the highest 50-msec. average dynamic loads on the top and second level strips, computed from the full-scale impact simulations and the crash test, were chosen as the controlling dynamic design loads. These loads were used in the calculation of recommended design pressures for the yielding of the strips. The simulation results for different strip lengths are shown in Table 9.17. The maximum total load for the top layer of strips was obtained from the simulation of the 24 ft (7.32 m) long strips and was 9.46 kips (42.08 kN). The maximum total load for the second layer of reinforcement strips obtained from the simulation was 2.19 kips (9.74 kN) also for the 24 ft (7.32 m) long strips. These values are comparable to those obtained from the simulation with 16 ft (4.88 m) strips. The associated maximum total loads are 8.52 kips (37.90 kN) and 3.21 kips (14.28 kN) for the first and second layers respectively. Since the tributary area associated with the 16 ft strips (3 strips per row per panel) is smaller than that associated with the 24 ft strips (2 strips per row per panel), higher yield pressures are obtained by using the maximum dynamic loads pertaining to the 16 ft strips. Table 9-17 Simulation results for TL-5-1 impact and calculation of design strip load for yielding design. Strip Length (ft) (1) Dynamic Load (kips) (2) Static Load(a) (kips) (3)=(1)+(2) Total Load (kips) (4) Calculated Resistance(b) (kips) Controlling Dynamic Design Load (kips) First Layer Second Layer First Layer Second Layer First Layer Second Layer First Layer Second Layer First Layer Second Layer 10 5.03 1.67 0.49 1.28 5.52 2.95 13.05 13.05 8.79 Selected from crash test results 16 8.03 1.93 0.49 1.28 8.52 3.21 13.05 13.05 24 8.97 2.19 0.49 1.28 9.46 3.47 13.05 13.05 (a)Calculated from AASHTO 11.10.6.4.3 (b)Reinforcement steel ASTM Grade 65
286 For the 16 ft (4.88 m) long strips with a density of three strips per panel per layer, the tributary area was 2.47 ft2 (0.23 m2) for the first layer, and 5.99 ft2 (0.56 m2) for the second layer. The controlling dynamic design loads for the top layer the second layer of strips, shown in Table 9- 18, were divided by the corresponding tributary areas to obtain the dynamic design pressures. The values obtained from the calculation were 3251.01 psf (155.66 kPa) and 483.71 psf (23.16 kPa) for the first and second layers respectively. To simplify the recommendations, 3250 psf (155.6 kPa) and 485 psf (23.2 kPa) were selected as the recommended dynamic design pressures for the top and the second layers, respectively. Table 9-18 TL-5-1 design pressure for yielding of soil reinforcement Layer Total Load (kips) Static Load* (kips) Dynamic Design Load (kips) Total Design Pressure, p Top (Simulation) 9.46 0.49 8.97 88970 lb./ 2.47ft2 (a) = 3631.58 psf (Final 3630 psf) Second (Simulation) 3.47 1.28 2.19 12190 lb./ 3.99 ft2 (b) = 548.87 psf (Final 400 psf)(c) (a) Tributary area of the panel for the top layer (2.47 ft2 = 4.87 ft à 1.52 ft / 3 strips per panel) (b) Tributary area of a panel for the second layer (3.99 ft2= 4.87 ft à 2.46 ft / 3 strips per panel). (c) The design pressure for pullout is used since it is more critical. To calculate the corresponding line load, the recommended pressures of 3250 psf (155.6 kPa) for the first layer and the 485 psf (23.2 kPa) for the second layer were multiplied by the tributary heights of 1.6 ft (0.49 m) and 2.5 (0.76 m), respectively (shown in Table 9-4). The calculated values are 5200 lb./ft (75.89 kN/m) for the first layer and 1212.5 lb./ft (17.70 kN/m) for the second layer. The simplified design values for the first and second layers of reinforcing strips are 5200 lb./ft and 1215 lb./ft respectively, as shown in Table 9-5. 9.3.7 Data for TL-5-2 1) Dynamic Load The dynamic design load for a MASH TL-5-2 impact is 261.8 kips (1165 kN) (Figure 9-29). To simplify the recommendations, a value of 260 kips (1157 kN) was selected. This load was selected based on results of FE analysis. This case applies to any barrier higher than 42 in. (1.07 m) where the floor of the trailer hits the barrier during the impact. No TL-5-2 crash test was performed in his study, but barriers taller than 42 in. (1.07 m) have been successfully crash tested as shown in Table 2-4. To prevent any damage to the underlying MSE wall and to minimize the relative displacement between barriers, the recommended length of the precast barrier section for a TL-5-2 impact is 15 ft (4.57 m). This length will enable the barriers to develop the complete failure mechanism (yield line) in the barrier face provided the coping is sufficiently strong. This is the
287 preferred failure mode of the barrier copingâmoment slab system because it reduces the cost of repair after a severe impact. Figure 9-29 TL5-2 (48 in) Impact Load versus Time. 2) Barrier-Moment Slab System TL-5-2 simulations were carried out for BMS systems with 9 ft (2.74 m) and 12-ft (3.66 m) wide moment slabs. The associated maximum displacements at the barrier top and coping level are shown in Figure 9-30 and Figure 9-31, respectively. Displacement criteria of 1.75 in. (44.75 mm) dynamic displacement at the top of the barrier, and 1 in. (25.4) permanent displacement at the barrier coping were applied for the TL-5-2 load case. Based on Figure 9-30, the maximum dynamic movement at the barrier top is 2.66 in. (67.56 mm) and 1.73 in. (43.94 mm) for the 9 ft (2.74 m) and 12-ft (3.66 m) wide moment slabs, respectively. Based on Figure 9-31, the permanent displacements at the coping level are 1.69 in. (43 mm) and 0.69 in. (18 mm) for the 9 ft (2.74 m) and the 12-ft (3.66 m) wide moment slabs, respectively. The system with 12-ft (3.66 m) moment slab was chosen as the basis for design because it satisfies both the dynamic and permanent displacement criteria. 261.8 kips
288 Figure 9-30 Maximum Displacements obtained at the top of a barrier of TL-5-2 tested straight barriers. Figure 9-31 Maximum Displacements obtained at the coping level of a barrier of TL-5-2 tested straight barriers. 3) Equivalent Static Load The recommended equivalent static load for TL-5-2 was obtained by considering the static resistance against sliding and overturning of the selected BMS system with 12-ft (3.65 m) wide moment slab (Figure 9-32). The resistance to sliding for this system is 132.45 kips (589 kN) and the resistance to overturning is 184 kips (818.5 kN). Since the resistance to sliding is more critical, it was used in the calculation of the equivalent static load. By using equation 9-2, an equivalent static load of 132.45 kips (589 kN) is obtained and 132 kN is adopted. Based on the simulation data, sliding occurs before overturning for this system. 0 0.5 1 1.5 2 2.5 3 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 Di sp la ce m en t ( in ) Time (s) Maximum TL5-2 Barrier Top Displacements TL5-2/ 9 ft. TL5-2/ 12 ft. -0.5 0 0.5 1 1.5 2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 Di sp la ce m en t ( in ) Time (s) Maximum TL5-2 Barrier Coping Displacements TL5-2/ 9 ft. TL5-2/ 12 ft.
289 Figure 9-32 TL-5-2 BMS system used in the calculation of resistance against sliding and overturning. A 12-ft (3.65 m) wide moment slab was consequently considered as the minimum required moment slab. The point of application of the load is 43 in. (1.09 m) measured from the roadway grade. It was concluded that a barrier taller than 42 in. (1.07 m) mounted to a 12-ft (3.65 m) wide (measured from the face of the panel), 30-ft (9.14-m) long moment slab is capable of withstanding a TL-5-2 impact while meeting the chosen displacement criteria, without considering the contribution of the surrounding soil at the interface area between the BMS system and the soil. 4) Wall Reinforcement The results of the MASH TL-5-2 full-scale impact simulations with reinforcement lengths of 10 ft (3.05 m), 16 ft (4.88 m) and 24 ft (7.32 m) for 9 ft (2.74 m) moment slab were provided, but those for the 12-ft (3.66-m) wide moment slab with 16 ft (4.88 m) reinforcement strip length were used to develop the guidelines for MASH TL-5-2 impact. The simulation results showed that the impact load was on average 260 kips (1157 kN). The maximum 50-msec. average dynamic loads in the strips, including the static load, and the wall displacement measured during the impact simulations are summarized in Table 9-19.
290 Table 9-19 Summary of the pullout resistance, maximum 50-msec. average strip load and wall displacement for MASH TL-5-2 impact simulation Strip Length/ Moment Slab Width (ft) AASHTO Pullout Resistance * (kips) Total Strip Load (kips) Dynamic Wall Displacement (in.) Approximate Permanent Wall Displacement (in.) First Layer Second Layer First Layer Second Layer Top (1) First Layer Second Layer Top (1) First Layer Second Layer 10/9 2.32 3.53 7.16 3.99 1.1 0.63 0.2 0.91 0.55 0.20 16/9 3.71 5.64 9.02 2.90 1.02 0.69 0.11 0.75 0.51 0.10 16/12 3.71 5.64 11.67 3.98 0.79 0.35 0.10 0.67 0.28 0.04 24/9 5.56 8.46 10.55 2.70 0.37 0.24 0.08 0.16 0.08 0.02 (1) Displacement measured at the coping level (2) Assuming Cu=D60/D10=4 as prescribed by AASHTO The strip loads presented in Table 9-19 were 7 in. (178 mm) from the face of the wall where the load is expected to be the highest. It is observed that the wall might experience an excessive permanent displacement (>0.75 in. (19.05 mm)) during a MASH TL-5-2 impact using 10 ft (3.05 m) strips that could potentially induce structural failure in the wall components. For this reason, the 10 ft (3.05 m) long strip reinforcement was not selected for pullout analyses. It was decided that the design recommendations be based on a pressure diagram approach that prescribes the pressure due to impact (in excess of static load) that must be resisted by the 16 ft (4.88 m) long strip reinforcement with a 12 ft (3.66 m) moment slab width and a density of three strips per panel in the first and second layer. This resulted in limited wall movements as shown in Table 9-19. Hence, the resulting equivalent design pressures should prevent excessive movement of the wall. a) Pullout of the Wall Reinforcement The design strip load in excess of static for the TL-5-2 impact simulation for the 16 ft (4.88 m) long reinforcement strip with a 12 ft (3.66 m) moment slab width was used to develop the design guideline for pullout of the reinforcement. The resistance (P) for the 16 ft (4.88 m) long strips was calculated to be 3.71 kips (16.50 kN) for the upper most layer and 5.64 kips (25.09 kN) for the second layer using Eq. (2-2) in Chapter 2 (AASHTO 11.10.6.3.2-1). The pullout friction factor F* was 1.59 for the upper most layer and 1.46 for the second layer. For the first layer, the total load (50-msec. average) in the strip was 11.67 kips (51.91 kN). Although the measured total load in the strip was higher than the resistance (3.71 kips (16.50 kN)), the displacement of the strips and performance of the wall were considered acceptable. In other words, the analyses indicated that a 16 ft (4.88 m) long strip will perform acceptably for a TL-5-2 impact due to the short duration of the event. Therefore, this resistance was used to obtain the dynamic design load in excess of the static load at the upper most layer. The controlling design load in excess of the static load due to static earth pressures was calculated to be 3.19 kips (14.19 kN). The value was found by calculating the factored total resistance of the 16 ft (4.88 m) long
291 strip at the depth of the first layer (3.71 kips (16.50 kN)) multiplied by a resistance factor of 1 minus the calculated load due to static earth pressures from AASHTO LRFD (0.84 kips (3.74 kN)). For the second layer, the same process was followed. The total load was 3.98 kips (17.70 kN). The static earth pressure load for the second layer was calculated to be 2.03 kips (9.03 kN) by AASHTO LRFD. The total load from the simulation (3.98 kips (17.70 kN) was less than the calculated pullout load at that depth (5.64 kips (25.09 kN)). Therefore, the measured dynamic load in excess of the static load was used as the controlling dynamic load for pullout design. Table 9-20 shows the total dynamic load obtained from the simulation, the calculated static load, the calculated pullout resistance, and the recommended design pressure for pullout resistance. Table 9-20 Simulation results of the TL-5-2 impact and calculation of design strip load for pullout design (1) Total (kips) (2) Static Load (kips) (3)=(1)- (2) Dynamic Load (kips) (4) Calculated Resistance (a) (kips) Controlling Design Dynamic Load (kips) Dynamic Design Pressure (psf) Top Layer 11.67 0.52 11.15 3.71 (4)-(2) = 23.19 3190 lb./2.57 ft2 (b) = 1241. psf (Final 1240 psf) Second Layer 3.98 1.29 2.03 5.64 (1)-(2) = 2.69 12691lb./3.96 ft2 (c) = 679.54 psf (Final 680 psf)(d) (a) Calculated from AASHTO 11.10.6.2 â 11.10.6.3, assuming Cu=D60/D10=4 as prescribed by AASHTO (b) Tributary area of the panel for the top layer (2.57 ft2 = 4.87 ft à 1.583 ft / 3 strips per panel) (c) Tributary area of a panel for the second layer (3.99 ft2 = 4.87 ft à 2.46 ft /3 strips per panel) (d) Used design pressure for pullout as determined for MASH TL-5-1 The dynamic pressure per strip was calculated as shown in Table 9-20. For the 16 ft (4.88 m) long strip with a density of three strips per panel at the top layer, the tributary area was 2.57 ft2 (0.24 m2). For the second layer with a density of three strips per panel the tributary area was 3.99 ft2 (0.37 m2). The dynamic design pressures in excess of the static earth pressure for pullout were calculated by dividing the controlling dynamic loads for the first and second layers by the corresponding tributary areas. This resulted in a value of 1241 psf (59.42 kPa) for the first layer, and 679.54 psf (32.54 kPa) for the second layer. The recommended pressures were selected as 1240 psf 59.37 kPa) for the first layer. For the second layer, 680 psf (32.56 kPa) was selected to match the design values determined for TL-5-1. b) Yielding of the Wall Reinforcement The reinforcement resistance to yielding (R) for a strip was calculated using Eq. (9-15). The tensile strength of the reinforcement (Ït) was 65 ksi (448 MPa) and the thickness, after accounting for corrosion loss (Ec), was 0.102 in. (2.59 mm) for a 75-year design life. The ultimate resistance R was computed to be 13.05 kips (58 kN).
292 To develop the design guideline against yielding of the reinforcement, the highest design load on any strip, computed from the full-scale impact simulations, was used; this was the load obtained in the simulation of the wall with 16 ft long strips and with the 12 ft (3.66 m) moment slab width. The maximum 50-msec. average total load on the strip located in the uppermost layer was 11.67 kips (51.91 kN). In the second layer, the total load was 3.98 kips (17.70 kN). The corresponding dynamic loads for the first and second layers are 11.15 kips (49.60 kN) and 2.69 kips (11.97 kN), respectively, as shown in Table 9-21. These loads were used as the controlling dynamic loads. Table 9-21 Simulation results for TL-5-2 impact and calculation of design strip load for yielding design Strip Length (ft) (1) Dynamic Load (kips) (2) Static Load(a) (kips) (3)=(1)+(2) Total Load (kips) (4) Calculated Resistance(b) (kips) Controlling Design Dynamic Load (kips) First Layer Second Layer First Layer Second Layer First Layer Second Layer First Layer Second Layer First Layer Second Layer 16 11.15 2.69 0.52 11.29 11.67 3.98 13.05 13.05 11.15 2.69 (a) Calculated from AASHTO 11.10.6.4.3 (b) Reinforcement steel ASTM Grade 60 The dynamic pressure per strip for yielding of the reinforcement was calculated as shown in Table 9-22. For the first layer, 16 ft (4.88 m) long strip with a density of three strips per panel per layer, the tributary area was 2.57 ft2 (0.24 m2). For the second layer, 16 ft (4.88 m) long strip with a density of three strips per panel per layer, the tributary area was 3.99 ft2 (0.37 m2). The dynamic design pressure for yielding of the reinforcement was calculated as 4338.5 psf (207.73 kPa) for the first layer, and 674.19 psf (32.28 kPa) for the second layer as shown in Table 9-22. A value of 4440 psf (212.59 kPa) was selected as a dynamic design pressure for the uppermost layer. To simplify the recommendations, 675 psf (32.32 kPa) was selected for the second layer to match the TL-5-1 recommendations for the second layer. The line loads for the first and second layer were obtained by multiplying the design pressure by the tributary heights of 1.6 ft (0.49 m) and 2.5 ft (0.76 m), respectively. For the first layer, a value of 7104 lb./ft (103.67 kN/m) was calculated. A simplified value of 7105 lb./ft was used in the recommendations. For the second layer, a value of 1687.5 lb/ft is obtained and 1690 lb/ft is adopted for simplification of the guidelines.
293 Table 9-22 TL-5-2 design pressure for yielding of soil reinforcement Layer Total Design Load (kips) Static Design Load (kips) Dynamic Design Load (kips) Dynamic Design Pressure, p Top 11.67 0.52 11.15 11150 lb./2.57 ft2 (a) = 4338.5 psf (Final 4440 psf) Second 3.98 1.29 2.69 2690 kips/3.99 ft2 (b) = 4674.19 psf (Final 675 psf)(c) (a) Tributary area of the panel for the top layer (2.57 ft2 = 4.87 ft à 1.583 ft / 3 strips per panel) (b) Tributary area of a panel for the second layer (3.99 ft2 = 4.87 ft à 2.46 ft / 3 strips per panel) (c) Used design pressure for pullout as determined for MASH TL-5-1
