Design Guidelines for Test Level 3 through Test Level 5 Roadside Barrier Systems Placed on Mechanically Stabilized Earth Retaining Walls (2022)

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226 8 STATIC LOAD TEST ON TL-5 BARRIER-MOMENT SLAB SYSTEM Upon completion of the full-scale TL-5 crash test, a static load test was conducted on a section of the BMS system (section B5-B6) on top of the MSE wall test installation. The objective of the static test was to assess the equivalent static load of the same TL-5 BMS system used for the full- scale dynamic test. 8.1 Static Analytical Solution The first part of the study was to estimate the force required to generate sliding (Fs) and overturning (Fo) of the BMS system using equilibrium equations. These forces were computed using Eq. (8-1) for sliding and Eq. (8-2) for overturning, as described in section 4: tans r r sF W f Aφ= + (8-1) where W= weight of the barrier, moment slab and soil of the section ϕ= angle of the internal friction of the soil tanϕr= interface friction between the soil and the moment slab (ϕr is taken as ϕ if the interface is rough (cast in place) and 2/3ϕ if the interface is smooth (precast concrete)). fr= shear strength resistance of the soil As= interface area of the soil in contact with the side of the moment slab 𝐹 = (8-2) where W= weight of the barrier, moment slab and soil of the section l= moment arm of the weight of the system h= moment arm of the equivalent static load applied to the system to the rotation point. xs= moment arm of the force associated with the shear strength of the soil A’s=interface area of the soil in contact with side and front edge of the moment slab The results of the analyses are summarized in

227 Table 8-1. The analytical solution shows that the sliding and overturning resistance of the system are similar in magnitude when the soil resistance is considered. Therefore, it is difficult to predict which failure mode will occur first. This explains why both modes existed during the impact test. This is not the case for lower impact levels, TL3 and TL4, where overturning of the barrier offers less resistance than sliding.

228 Table 8-1 Results of the analytical solution of the TL-5 test BMS system Test Level W (kips) Moment Arms around Rotation Point B Sliding Analyses Overturning Analyses Rotation Point B TL-5-1 128.6 lB (in) hB (in) FS (kips) Fs+soil (kips)(1) Fo (kips) Fo+soil (kips) 34.5 59.3 86 90.5 74.8 93.3 (1) Strength of the soil was only considered at the side faces of the moment slab and not at the front. The value was 126 psf as backcalculated from NCHRP Report 663. 8.2 Quasi-static FE Analyses To further study the static response of the system, an FE analysis was conducted on the BMS portion of the MSE wall model. The shear dowels connecting the moment slabs were removed to isolate the different sections. The interface between the soil and the moment slab were modeled using contact elements to capture the force generated between the soil and the moment slab. The analysis was conducted by applying a prescribed displacement rate to a block that was used to distribute the applied load. The displacement was applied at a very low rate to avoid inertial effects. The length of the block was 10 ft (3.05 m) as recommended in section 3 for the TL-5 load distribution in the longitudinal direction (Figure 8-1). The load was applied at an effective height of 34 in. (864 mm) from the roadway surface. The set-up of the quasi-static FE model is shown in Figure 8-1. The analysis was conducted using rotation point B between with the barrier sections mounted on top of the MSE wall panels. The result of the quasi-static FE analysis is presented in Figure 8-2. Although the primary failure mode of the barrier-foundation system is overturning, the system also slides considerably. This result is highly dependent on the friction developed at the interface between the coping and the concrete leveling pad. The simulation indicates that the ultimate static load is approximately 100 kips (445 kN). At this load level, the displacement of the barrier at the top, ground surface, and bottom were 0.65 in. (16.51 mm), 0.43 in. (7.62 mm) and 0.23 in. (5.84 mm), respectively.

229 a) Longitudinal distribution of the quasi-static load b) Application height of the quasi-static load Figure 8-1 Quasi-static FE analyses set-up for the test BMS system. B

230 Figure 8-2 Results of the quasi-static FE analyses in the test barrier-foundation system. 8.3 Full-Scale Static Load Test The purpose of the static load test was to verify the magnitude of the static load applied to the barrier required to initiate movement of the BMS system. The set-up for the static load test of the barrier system is illustrated in Figure 8-3 and Figure 8-4. A steel-reaction frame was anchored to an existing concrete deck. The load was applied at an effective height of 34 in. (864 mm) above the finished grade by means of a hydraulic cylinder. A spreader beam with a wood-block attached to its face was used to distribute the load over a longitudinal barrier length of 10 ft (3.05 m). The applied pressure from the hydraulic cylinder was measured and converted into force. The load was applied continuously at a slow rate of 5 kips (22.25 kN) per minute in order to reduce inertial effects of the system. The displacement of the barrier, the coping, and the moment slab was recorded digitally using calibrated string pot sensors. The three string pots on the barrier were positioned on the excavation side in the center of the loaded section of the barrier the top edge, ground level, and bottom. The displacement measurement devices were secured to a steel frame located at the back side of the wall. For the moment slab, the string pots were positioned at each edge and at the center point of the 30 ft (9.15 m) moment slab section. When the lateral load applied to the top of the barrier reached about 80 kips (356 kN), the soil began to crack along the edges of the moment slab, as shown in Figure 8-5. The load test was stopped at a load of 100 kips (445 kN). 0 25 50 75 100 125 0.00 0.20 0.40 0.60 0.80 St at ic L oa d (k ip s) Barrier Displacement (in.) Top (A) Ground Level (B) Bottom (B) A C B

231 Figure 8-3 Details of the full-scale static test set-up on the barrier-foundation system. 45° 1' Clean sand material Road base material Existing Deck 2'-10" Steel rod (Ø 1.75") TS1 4x1 4x1 /2 Hydraulic Ram Steel Frame 6° Steel rod bar 2'-10" String pot (Barrier top) String pot (Ground level) String pot (Barrier bottom) U-channel to support the string pot Finished grade 3'-6" 7'-1" 10' 3'-4" 45° Spreader Beam

232 Figure 8-3 Details of the full-scale static test set-up on the barrier-foundation system (Continued). NORTH 30' 7'-1" B-5 B-6 C-13 C-14 C-15 C-16 C-17 C-18 45° 10' 10' 8" 1 2" STEEL ROD New ground level SOUTH String pot location at the moment slab (2.5" from moment slab edge to center) Steel rod bar location 2.5" 2.5"moment slab edges 5' Compacted road base At moment slab mid-point location 2"x2" Unistrut for support of string pot over moment slab Ø 18" Strip B5_B_1st(A)

233 a) Side view of the static test set-up b) Overall view of the static test set-up Figure 8-4 Photograph of the full-scale static test set-up.

234 Figure 8-5 Crack in the soil during the static load test The steps of the static test were as follows: a) The system was loaded up to 100 kips (445 kN). The displacement at the top of the barrier at this load level was 0.5 in. (12.7 mm). b) The system was unloaded to zero load. The residual displacement at the top of the barrier was 0.25 in. (6.35 mm). c) The system was re-loaded from zero to 80 kips (356 kN). The displacement at the top of the barrier after re-load was 0.43 in. (10.92 mm). d) The load was increased from 80 kips (kips) to 100 kips (445 kN) in steps of 5 kips (22.25 kN) per minute. The displacement at the top of the barrier was 0.50 in. (12.7 mm). d) After the load reached 100 kips (445 kN), it was held at that load for one minute. The displacement increased from 0.50 in. (12.7 mm) to 0.54 in. (13.7 mm). The load displacement curve generated from the test data is shown in Figure 8-6(a). The load-deflection response of the BMS system was close to being linear up to a load of 75 kips (190.5 kN). This load corresponds quite well with the load capacity of the 30 ft (9.15 m) long barrier- moment system based on the static equilibrium analysis when ignoring soil friction (Table 8-1). Figure 8-6(b) indicates that the top of the barrier had moved 0.15 in. (3.81 mm) at a load of 75 kips (190.5 kN). As the load increased beyond 75 kips (190.5 kN), the displacement of the barrier increased in a nonlinear manner. The results also indicate sliding movement at the bottom and at the ground level of the barrier (Figure 8-6(b)). At a load of 100 kips (445 kN), the displacement at the top of the barrier, at ground level and at the bottom were 0.54 in. (13.71 mm), 0.30 in. (7.62 mm) and 0.15 mm (3.81 mm), respectively. When the load test was stopped, the load-deflection curve was nearly asymptotic indicating the shear strength of the soil had been exceeded.

235 a) Load and re-load displacement curve b) Load displacement curve at different location Figure 8-6 Results of the full-scale static test on the barrier-foundation system. Figure 8-7 shows the variation of the vertical displacement of the moment slab with the applied static load to the barrier system. The vertical displacement of the moment slab was measured by string pots (SP) located at the upstream end (SP-A), center (SP-B) and downstream end (SP-C) of the moment slab. The maximum vertical displacement of the moment slab was 0.17 in. (4.3 mm) at the upstream end section. The displacements at the three locations were similar. Figure 8-7 also shows that the vertical displacement of the moment slab increases once the static 0 25 50 75 100 125 0.00 0.15 0.30 0.45 0.60 St at ic L oa d (k ip s) Top Barrier Displacement (in.) Unload Reload 0 25 50 75 100 125 0.00 0.15 0.30 0.45 0.60 St at ic L oa d (k ip s) Barrier Displacement (in.) Top (A) Ground Level (B) Bottom (C) A C B

236 load reaches a magnitude of 75 kips (333.8 kN), which is associated with the static capacity of the system to overturning discounting the shear resistance of the soil. Figure 8-7 Vertical displacement of moment slab and applied static load. During the static test, the load in strip section B5-B-1st(A) was recorded at every load increment of 5 kips (22.25 kN) in the barrier. The strip was positioned below barrier segment 5 and the strain gage was located 7 in. (177.8 mm) from the face of the panel. This strip was previously used to capture the dynamic load from the TL-5 full-scale crash test. The load–time history is presented in Figure 8-8. It is observed that the load in the strip increases more rapidly after the static load reaches a magnitude of 80 kips (356 kN), which corresponds to the load that initiated excessive movement in the barrier. It was further observed that the barrier system was not only rotating around its longitudinal axis but also around its vertical axis. This unexpected movement was associated with additional friction developed at the interface of the moment slabs joints between barrier segments 4 and 5. At the joint between barrier segments 6 and 7, the sliding component of the movement was around 0.5 in. (12.7), as shown in Figure 8-9 and Figure 8-10. After the test, the relative displacement of barrier segments 6 and 7 at the bottom of the joint between them was about 1.0 in. (25.4 mm). Prior the test, this relative offset was about 0.4 in. (10.2 mm) to 0.5 in. (12.7 mm). 0 25 50 75 100 0.00 0.05 0.10 0.15 0.20 A pp lie d St at ic L oa d (k ip s) Moment Slab Displacement (in.) SP-A SP-B SP-C A B C Barrier Moment Slab

237 Figure 8-8 Time history load of the strip during the static test. Figure 8-9 Sketch of movement of the barrier system during the static test. -0.2 0.0 0.2 0.4 0.6 0.8 1.0 0 5 10 15 20 25 St rip L oa d (k ip s) Time, (minutes) B5_B_1st(A) Static Load, 80 kips Static Load Rate in the Barrier, 5 kips/min. LOAD Rotation Sliding LOAD Rotation Sliding

238 Figure 8-10 Relative movement at the bottom of barrier segment 6 and 7 during the during the static test. Upon completion of the static test, a visual inspection of the underlying MSE wall was conducted. Some of the wall panels located underneath barrier segments 5 and 6 experienced relative movement between them in the vertical and longitudinal direction ( Figure 8-11). The wall panels were originally installed with a nominal joint spacing of 0.75 in. (19.05 mm) ± 0.2 in. (5.1 mm). In addition, this portion of the wall was not significantly affected by the impact test conducted prior to the static load test as observed in the permanent deflection measurements described previously. The vertical movement was minimal (less than 0.25 in. (6.35 mm)) and was associated with the high compressive load imposed by the barrier system during its rotation on top of the concrete leveling pad and wall panels. The relative movement in the longitudinal direction was more significant and it ranged from 0.2 in. (5.1 mm) to 0.5 in. (12.7 mm). The longitudinal movements of the panels were associated with the uneven deflection of the system observed in the north section of the BMS system (refer to Figures 7-17 and 7-18).

239 Figure 8-11 Relative panel movement observed during the static load test. 8.4 Comparison of Test and Simulation Figure 8-12 shows the load test results compared to the numerical simulation. The FE analyses estimated the load reasonably well (within 7% difference). Additional friction was developed at the interface of the test moment slab with its neighbor sections, which may explain the difference between the test and the simulation beyond an applied load of 65 kips (289.3 kN). This comparison between the test and simulation indicates that the static resistance is comprised of two components: the component due to the weight of the moment slab and overburden soil, and the component due to the friction between the moment slab-overburden soil and the surrounding soil. Back-calculations indicate that the average shear strength of the concrete–soil interface at that shallow depth was 266 psf (12.74 kPa), which is approximately 15%

240 of the cohesion intercept estimated from the triaxial test. As explained previously, the friction component might not be attributable entirely to the soil. Figure 8-12 Comparison of static test and FE static model. 8.5 Conclusion The following conclusions are based on and limited to the content of this chapter: The primary failure mode of the system was overturning since it occurred before sliding. This was shown analytically and confirmed in the full-scale static test However, there was also significant sliding observed. This confirms that both criteria should be checked. The results of the test also validate the equivalent static load proposed to design the BMS system against a TL-5-1 impact. In addition, it provides a level of confidence in the FE analyses conducted for other test levels. 0 25 50 75 100 125 0.00 0.20 0.40 0.60 0.80 St at ic L oa d (k ip s) Top Barrier Displacement (in.) Test FEA