Design Guidelines for Test Level 3 through Test Level 5 Roadside Barrier Systems Placed on Mechanically Stabilized Earth Retaining Walls (2022) / Chapter Skim
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39 3 PEAK DYNAMIC LOAD The objectives of this portion of the study are to update the design impact loads for TL-3 impacts and to quantify the design impact loads for TL-4 and TL-5 impacts. The analysis work includes the prediction of impact loads based on measured test data and FE impact analyses using the commercial FE software LS-DYNA (6)
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40 model was not available for the previous study and, therefore, MASH TL-3 impact loads were not updated in NCHRP Report 663 (2)
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41 Figure 3-3 2000P pickup truck impact force on barrier (50-msec. average)
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43 a) x-acceleration (Test 475350-1)
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44 Figure 3-7 MASH TL-3 impact force versus time history for barrier impact (50-msec. average)
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45 velocity, impact angle, vehicle dimensions, weight and stiffness of the system on the magnitude of the impact load. This approach, which is shown in Eq.
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46 ( ) 22050 4.5 32.2 99 32.2impact total lat F m a kips= × = × × = (3-4)
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48 b) x-acceleration (Test 476460-1b)
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49 b) Barrier Height Variation Analyses FE impact simulations were conducted on rigid barriers of different heights: 36 in.
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50 The distribution of the impact force in the longitudinal and vertical directions was studied for each barrier. The rigid barriers were discretized into multiples segments.
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51 a) Lateral impact force (Ft)
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52 a) Lateral impact force (Ft)
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53 a) Lateral impact force (Ft)
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54 a) MASH lateral impact force (Ft)
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55 A summary of the magnitude, distribution and application of the resultant MASH TL-4 impact loads for the different barriers is presented in Table 3-1. There are three forces involved: Ft is the transverse force which is applied perpendicular to the barrier otherwise referred to as the impact force, FL is the longitudinal force which is applied by friction along the direction of the barrier, and Fv is the vertical force which is applied downward on the top of the barrier.
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57 acceleration of the SUT box onto the top of the barrier due to increased lateral engagement of the box by the barrier and an associated decrease in roll. The influence of the barrier height is also evident in the longitudinal and vertical distribution of the lateral impact load.
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58 Alternatively, Eq.
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59 Table 3-2 Computation of impact dynamic forces using the equation of motion Test No (Refer.
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60 a) FE tractor model b)
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61 the lower bound model (42 in.
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62 a) Lateral impact force (Ft)
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63 f) Longitudinal distribution, LL (t=0.832 sec.)
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64 a) Lateral impact force (Ft)
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65 f) Longitudinal distribution, LL (t=0.731 sec.)
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66 d) Longitudinal distribution, LL (t=0.183 sec.)
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67 a) Lateral impact force (Ft)
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68 e) Longitudinal distribution, LL (t=0.70 sec.)
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69 Figure 3-23 Variation of impact force for different barrier heights for MASH TL-5.
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70 The peak lateral loads associated with the taller barriers are greater than the load measured in the instrumented wall tests conducted by TTI researchers in the 1980's. The primary reason for this is the difference in the ballast.
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71 magnitude of the impact load. The recommendations for MASH TL-5 account for the highest of the three impact loads imposed by the tractor-trailer on a barrier of a given height.
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