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140 6 TL-4 FULL-SCALE TEST ON TOP OF A 10-FT HIGH MSE WALL A TL-4 full-scale crash test was performed to validate the preliminary design guidelines and/or modify them as necessary. An FE analysis was performed using LS-DYNA to help plan and predict the outcome of the TL-4 crash test. 6.31 Description of the Barrier-Moment Slab and MSE Wall The precast concrete barrier-coping sections used in the TL-4 test installation were 10 ft (3.05 m) long and had a single-slope traffic face with an 11-degree angle from vertical. The units had an overall height of 5 ft-3 in. (1.58 m), a width of 24 in. (0.61 m) at the bottom of the coping, and a width of 7.5 in at the top of the traffic barrier section (Figure 6-1). The 36-in. (0.91 m) tall barrier height above the finished grade is the minimum height required to contain and redirect a MASH SUT impacting the at a speed of 56 mph (90.12 km/hr) and an angle of 15 degrees. An aesthetic recess on the field side of the barrier was cast at the plant. Figure 6-1 RECO Single-Slope shape concrete barrier details. The total length of the test installation was approximately 150 ft (45.7 m) as shown in Figure 6-2. The first 90 ft-4 in. (27.55 m) of BMS were placed on top of a 9.8-ft (2.99 m) tall MSE wall. The remaining 60 ft-3 in. (18.36 m) consisted of the same roadside barrier and moment slab section with no underlying MSE wall. This extension of the test installation was added to ensure complete containment and redirection of the SUT. The MSE wall used for the test was previously constructed for the TL-3 test previously conducted under NCHRP Project 22-20. Details of the TL-3 MSE wall can be found in NCHRP report 663. The wall was rehabilitated and re- instrumented to meet the requirements of the TL-4 crash test. A cross section of the barrier and MSE wall system constructed for the TL-4 crash test is shown in Figure 6-3.
141 Figure 6-2 Overall Layout of the TL-4 MSE wall installation showing critical IP (CIP). Figure 6-3 Side view of the TL-4 test wall installation with 36-in. (0.91 m) tall barrier. Three 10 ft (3.05m) long precast barrier units were attached to each of three 30-ft (9.15-m) long moment slabs. The width of the moment slabs was 5.2 ft (1.58 m) as measured from the inside face of the wall panels. The moment slabs were cast in place with a specified concrete compressive
142 strength (fâc) of 4000 psi (27.6 MPa). The barrier sections and the moment slabs were connected using No.6 L-bars at 10 in. (0.25 mm) on center. The three moment slab sections were connected to one another using three No.9 shear dowels across each joint. The MSE wall was originally constructed for the TL-3 crash test in 2008 by excavating a trench adjacent to an existing concrete apron. A 12-in. (0.30 m) wide by 6-in. (0.15 m) thick unreinforced concrete leveling pad was poured at the bottom of the trench to serve as a level foundation for the MSE wall panels. Eighteen precast MSE wall panels (one full and one half-panel per section) were installed on top of the leveling pad. The 5.5 in thick panels measured 5 ft 7.5 in. (1.71 m) wide by 4 ft 10.25 in. (1.48 m) tall for the full panels, and 5 ft 7.5 in. (1.71 m) wide by 2 ft 6.125-in. (0.77 m) tall for the half- panels. The AASHTO MASH was followed for the full-scale crash test. The TL-4 test followed MASH test designation 4-12 impact conditions. This test involves a 10000S vehicle weighing 22,000 lb. ±660 lb. (9979.03kg ± 300 kg) impacting the barrier at an impact speed of 56 mph ±2.5 mph (90.12 km/h ± 4.00 km/h) and an angle of 15 degrees ±1.5 degrees. 6.1.1 Calculation of MSE Wall Capacity The force expected in the 10 ft (3.05 m) long reinforcement strips due to the gravity load was computed according to AASHTO LRFD (3). The preliminary design pressure distributions of MSE wall reinforcement recommended in Chapter 5 were used to estimate the dynamic loads on the strips resulting from a TL-4 impact. The information obtained from these analyses is summarized in Table 6-1. Table 6-1 Pullout unfactored resistance and force in the reinforcing strips for TL-4 MSE wall Layer Strips Length (ft) Depth (ft) Tstatic(1) (kips) Tdynamic(2) (kips) Ttotal= Tstatic +Tdynamic (kips) P Resistance(3) of Pullout (kips) Top 10 3.0 0.69 1.26 1.95 1.95 (F*=1.63) Second 10 5.5 1.20 2.03 3.23 3.23 (F*=1.49) (1) AASHTO LRFD (2) Using preliminary pullout pressure of 348 psf (first layer) and 508 psf (second layer) for TL-4-1 obtained by dividing the dynamic load by the tributary areas of 3.62 ft2 and 3.99 ft2 for the 1st and 2nd layers respectively. (3) According to AASHTO LRFD Eq. 11.10.6.3.2-1, Table 5-2. 6.1.2 Calculation of the Barrier Capacity The 36-in. (1.07 m) tall single-slope shape barrier was designed for an impact load of 70 kips (311.38 kN) applied at a height of 25 in. (0.64 mm). Figure 6-1 shows the cross section detail of the precast single-slope barrier used in the TL-4 crash test.
143 The ultimate load capacity of this barrier was computed to be 69 kips (306.9 kN) using the end section yield line analysis procedure described in AASHTO LRFD (3). The critical length required to develop the end section failure mechanism is about 4.3 ft (1.31 m). Since the barrier length is 10 ft (3.05 m), it is not practical to specify a variation in the vertical reinforcement spacing between the interior and end regions, so the same reinforcement spacing was used throughout. The steel reinforcement in the coping and moment slab was designed to provide sufficient strength to develop the strength of the barrier. This was done by analyzing the strength of the critical sections (sections A-A and B-B in Figure 6-1). 6.31 Finite Element Analyses The MSE wall model used to evaluate the TL-4 impact performance in Chapter 5 was modified to reflect the details of the proposed full-scale test installation. The modifications included the incorporation of the TL-4 single-slope barrier model with explicit reinforcement details as shown in Figure 6-4. Figure 6-4 TL-4 BMS system model of the TL-4 test installation. The total weight of the system was calculated and used as a convergence criterion for the initialization of the model under steady-state gravity. The total weight of the system model for the 36 in. (0.91 m) barrier, 5.2-ft ( 1.58 m) wide moment slab, and MSE wall was 2,453 kips (10,912 kN) using the mass of the FE model and the acceleration of gravity.
144 Figure 6-5 shows the calculated and the simulated weight of the system after gravity initialization. There was good agreement between the calculated and simulated weight. The initialized model was then set up with the SUT vehicle model for the TL-4 impact simulation, as shown in Figure 6-6 and Figure 6-7. Figure 6-5 System reaction force of the TL-4 MSE wall test installation model. Figure 6-6 Downstream view of the TL-4 MSE wall model.
145 (a) Elevation view of the test installation model (time of impact) (b) Top view of the test installation model (time of impact) Figure 6-7 TL-4 MSE wall and SUT vehicle model. The simulation results indicated that the SUT vehicle model was successfully contained and redirected by the 36-in. (0.91 m) tall BMS system. The barrier and wall panel displacements were within the desired limits. Figure 6-8 shows sequential images of the vehicle impact event.
146 a) Pre-impact time position b) Initial impact (t=0 sec.) c) First peak load ( t=0.1 sec.) d) Second peak load (t = 0.235 sec) Figure 6-8 Vehicle position at each significant time for the test wall installation model. 6.2.1 Lateral Impact Load on Barrier The magnitude of the lateral impact force is shown in Figure 6-9. The 50-msec. average force-time history indicates the first load peak is 66.8 kips (298 kN) and the second load peak is 68.2 kips (304kN).
147 Figure 6-9 50-msec. average impact load on the single-slope TL-4 barrier. 6.31 TL-4 Crash Test Detailed descriptions of the construction of the MSE wall and the crash test are presented in the following sections. The construction of the MSE wall followed standard reinforced earth construction procedures, and the TL4 crash test was conducted in accordance with the MASH specification. 6.3.1 Test Planning and Set Up This section presents the construction steps followed to prepare the TL-4 test installation. Detailed construction drawings are shown in Appendix B. The construction procedure was planned to transform the previous TL-3 system into a TL- 4 system. The ground surface was excavated down to the level of the TL-3 moment slab. The TL- 3 barrier sections, moment slabs, and the leveling pad on top of the wall panels were removed. Excavation continued to the first level of soil reinforcement strips. The strips in the impact region were replaced by eight (8) new instrumented strips at the selected locations. Additional excavation to the second layer of soil reinforcement was made at one location to instrument the critical strip based on the FE simulations results. These strips were instrumented with new strain gages to capture the dynamic load associated with the impact. The fill was then placed and compacted up to the level of the new moment slab. A new leveling pad was cast on top of wall panels, and the TL-4 barrier-coping sections were then placed on top of the leveling pad. The moment slab reinforcement was place (Figure 6-10), and the moment slab was then cast in place (Figure 6-11). Road base was then placed and compacted on top of the moment slab in layers to the specified grade (Figure 6-12). The completed test installation is shown in Figure 6-13.
148 Figure 6-10 Moment slab reinforcement. Figure 6-11 Casting of moment slab. Figure 6-12 Compaction of fill in layers till ground level. Figure 6-13 Three-dimensional view of the installation. 6.3.2 Instrumentation Instrumentation was installed to measure forces in the soil reinforcement strips and displacements of the barrier sections and wall panels through electronic and photographic methods. The test vehicle was instrumented with accelerometers and an on-board data acquisition system (Figure 6- 14). The accelerometers were used to measure the vehicle acceleration along the three (3) vehicle axes x, y and z. Angular rate sensors (rate gyros) were used to measure the roll, pitch and yaw rates of the vehicle. An accelerometer was also installed at the front edge of the moment slab on the traffic side near the location of impact. At the same location along the wall, a 6 in. (15.24 cm) long tape switch was attached at the top front edge of the wall panel to determine if the coping made contact with the wall panel during the impact. Eight of the soil reinforcing strips were instrumented with full- bridge strain gages to measure the load in the strip during construction and during the impact (Figure 6-15). The strips were distributed as follows: seven strips in the top layer of reinforcement in the impact region, and one strip in the second layer of reinforcement at the critical location indicated by the FE simulation. The instrumentation details are shown in the construction drawings presented in Appendix B.
149 Figure 6-14 On-Board data acquisition system. Figure 6-15 Instrumented reinforcement strips. Photographic instrumentation included three high-speed digital cameras: one overhead with a field of view perpendicular to the ground surface and directly over the IP; a second placed behind the installation at an angle to monitor the wall and the barrier response; and a third placed to have a field of view parallel to and aligned with the barriers at the downstream end. Five (5) targets were attached to the wall panels and the barrier sections near the impact location to track the relevant dynamic displacements using high-speed video analysis (Figure 6-16). Still cameras were used to record and document the test vehicle and installation conditions before and after the test. Additionally, a total station was used to record the coordinates of selected points before and after the crash test to determine permanent movement of the barrier sections and wall panels (Figure 6-17). Figure 6-16 Targets placed on the barrier and panels. Figure 6-17 Measurements for permanent displacement before the test.
150 6.3.3 TL-4 Crash Test Details of the MASH TL-4 crash test are documented in the following sections. Test Designation MASH test 4-12 involves a 10000S vehicle weighing 22,000 lb. ±660 lb. impacting the bridge rail at an impact speed of 56 mi/h ±2.5 mi/h and an angle of 15 degrees ±1.5 degrees. For the purpose of this test, the CIP was selected in accordance with MASH guidance to be 60 inches upstream of the joint between barriers 5 and 6 (Figure 6-2). Actual Impact Conditions The truck used in the crash test was a 2004 International 4200 single-unit box-van (Figure 6-18). It weighed 22,040 lb. (9,997 kg). The actual impact speed and angle were 58.5 mi/h (94 km/hr) and 15.2 degrees, respectively. The actual IP was 5.7 ft (1.74 m) upstream of the joint between segments 5 and 6. The target IS was 154.5 kip-ft, and the actual IS was 173.3 kip-ft (+12%). Photographs taken during the impact are shown in Figure 6-19. Additional sequential photographs of the impact are presented in Appendix C. Figure 6-18 SUT used in the TL-4 crash test.
151 Figure 6-19 Downstream and overhead photographs of the TL-4 crash test. 6.3.4 Reported Damage Damage to the barrier system after the test is shown in Figures 6-20 and 6-21. Figure 6-20 shows the damage in barrier section no. 4 (shown in Figure 6-2). Figure 6-21 shows the damage on the face of barrier no. 5 on the traffic side. No damage occurred in the wall panels or coping sections. As shown in Figure 6-22, a crack occurred in the compacted fill at the edge of the moment slab. Figure 6-20 Damage in barrier number 4.
152 Figure 6-21 Post-crash views of the barriers from the traffic side. Figure 6-22 Crack in the compacted fill over the edge of the moment slab. 6.3.5 Test Results The following sections present results obtained from the instrumentation of the vehicle and wall system including acceleration of the vehicle CG, displacement of the barrier sections and wall panels, and strain gage data for the reinforcement strips.
153 Data from Accelerometers The data gathered from accelerometers and angular rate sensors are presented herein. The sign convention adopted for the data analysis is shown in Figure 6-23. Plots of acceleration versus time in the x, y and z directions are shown in Figures 6-24 through 6-26. The maximum 50-msec. average acceleration in the x-direction is 2.5g as shown in Figure 6-24. The 50-msec. average maximum acceleration in the y-direction is approximately 4g (Figure 6-25). Figure 6-23 Sign Convention used in data processing. Figure 6-24 Acceleration in the x-direction at truck CG.
154 Figure 6-25 Acceleration in the y-direction at truck CG. Figure 6-26 Acceleration in the z-direction at truck CG. The impact forces in the x-direction (Fx) and the y-direction (Fy) are calculated using the 50-msec. average acceleration value and the mass of the vehicle (22,040 lb. (9,997.18 kg)). These forces were used to compute a resultant impact force R perpendicular to the face of the barrier. The Fx and Fy forces in the x and y directions are shown in Figure 6-27. The resultant impact force R is plotted versus time in Figure 6-28.
155 Figure 6-27 Plot of forces calculated from vehicle accelerations. The initial impact (1) and the back-slab (2) are clearly identified in Figure 6-28. The maximum forces obtained from this figure are 105 kips (468 kN) and 57 kips (254 kN) due to the first impact and the back-slab respectively. A plot of the roll, pitch and yaw angles versus time is shown in Figure 6-29. The maximum roll angle of the SUT was approximately 43 degrees. Figure 6-28 Plot of resultant force versus time.
156 Figure 6-29 Roll, Pitch and Yaw plot versus time. Data from Photographic Instrumentation Dynamic Displacement â The dynamic displacement at the top of the barrier was obtained from the analysis of high-speed video using the targets affixed to the back of the barrier sections and wall panels. The dynamic movement of the top of the barrier versus time is shown in Figure 6-30. The negative displacement values indicate movement of the barrier in the direction of the impact force. The estimated maximum dynamic displacement at the top of the barrier is 0.863 in. (2.19 cm). Figure 6-30 Dynamic movement at the barrier top versus time.
157 Permanent Displacement â The permanent displacement at the top of the barrier was measured using a total station to be approximately 0.31 inches (0.8 cm), which is consistent with the dynamic movement after the impact as shown in Figure 6-30. b) Data from Instrumented Strips The distribution of the instrumented strips in the wall is shown in Figure 6-31. Plots of the forces in the strips versus time for each strip is displayed in Figure 6-32 based on the strain gage measurements at each location. A maximum dynamic strip load of 2.4 kips (10.68 kN) was measured in the top reinforcement layer. This exceeds the calculated AASHTO pullout resistance of 1.95 kips (8.67 kN) indicating that the strip may have momentarily been at failure during the impact. Figure 6-31 Locations and labels of the instrumented reinforced strips.
158 Figure 6-32 Force measurements from readings of the strain gages installed on the reinforcement strips.
