Criteria for Restoration of Longitudinal Barriers, Phase II (2021) / Chapter Skim
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109 CHAPTER 7 – DEVELOPMENT AND VALIDATION OF THE G4(2W) GUARDRAIL MODEL Model Development A detailed finite element model of the G4(2W)
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110 Figure 72. Finite element model of the G4(2W)
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111 Splice Connection Model An important consideration in modeling the w-beam rails is the splice connections that fasten the individual rail sections together. The splice is often the point where structural failure occurs during impact.
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112 Figure 74. Components of the finite element model of a weak-post w-beam guardrail splice used in Ray et al.
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113 Figure 76. Test setup and axial force-displacement graphs from uniaxial tension tests of guardrail splices.
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114 Guardrail Posts The cross-section dimensions of the wood guardrail posts and blockouts were 6 x 8 inches; the length of the posts was 64 inches. The wood material was modeled with mechanical properties consistent with Southern Yellow Pine.
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115 tests involved a 2,372-lb rigid-nose pendulum striking the posts at 21.5 inches above grade. The posts were 66 inches long and were embedded 38 inches inside a 12x12 inch steel tubular sleeve with "rigid" fixity.
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116 The differences between the FEA results and tests indicate that the pendulum head, as well as the boundary conditions, were softer in the test. Table 28.
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117 Figure 77. Test set-up and FEA model used in wood-model validation.
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118 Figure 79. Energy vs.
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119 Figure 80. Force vs.
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120 Figure 82. Sequential views of (a)
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121 Figure 83. Force vs.
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122 The Lagrangian and Eulerian element types are the traditional formulations used in stress analysis as well as crash analysis; although ALE, EFG and SPH formulations may be better suited to modeling fluid type behavior. All these element formulations can be mixed and often are to model fluid-structure interactions.
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123 Figure 85. Soil springs attached directly to post.
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124 Figure 86. Soil modeled with non-linear springs and contact plates.
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125 properties with the dimensions similar to those of the physical device. The pendulum model struck the face of the post at 24.88 inches above grade at an impact speed of 20.0 mph.
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126 Limitations of the model The effects of dynamic loading of the soil (e.g., inertial spikes) are not accounted for in this model, although they could be modeled using discrete damper elements with empirically defined properties.
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127 downstream direction. The initial point of contact was approximately 2-ft upstream of the wbeam rail splice connection at Post 14.
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128 Figure 90. Comparison of properties for the test and analysis vehicle.
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129 The pitch angle was 9.1 degrees and decreasing, The yaw angle was 26.15 degrees relative to the barrier, and The forward velocity of the vehicle was 37.3 mph. Damage to Test Installation The installation received moderate damage as shown in Figure 91.
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130 Figure 91. Comparison of G4(2W)
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131 The occupant risk assessment measures were computed using the three acceleration timehistories and the three angular-rate time histories collected at the center of gravity of the vehicle. The Test Risk Assessment Program (TRAP)
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132 Figure 92. Sequential views of TTI Test 471470-26 and FE analysis from overhead viewpoint.
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133 Figure 92.
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134 Figure 93. Sequential views of TTI Test 471470-26 and FE analysis from downstream viewpoint.
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135 Figure 93.
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136 Figure 94. Sequential views of TTI Test 471470-26 and FE analysis from an oblique viewpoint behind the system.
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137 Figure 94.
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138 Table 30. Summary of phenomenological events of full-scale test 471470-26 and FEA simulation.
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139 Figure 95. Location of accelerometer in FE model.
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140 Table 31. Summary of occupant risk measures computed from Test 471470-26 and FEA simulation.
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141 Figure 96. Longitudinal acceleration-time history plot from accelerometer at c.g.
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142 Figure 99. Yaw-time history plot from accelerometer at c.g.
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143 Summary The intent of this qualitative evaluation was to verify overall model response through a general comparison with a full-scale crash test. The general response of the FE model seemed reasonable in that the model provided the basic chain of phenomenological events that occurred in the full-scale crash test.
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144 Sprague & Geers: 22 22 1 2 2 ) ( iveComprehens cos1)
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145 o Phase should be less than 40 percent ANOVA metrics o Mean residual error should be less than 5 percent o Standard deviation should be less than 35 percent. Phenomena Importance Ranking Tables (PIRT)
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146 Table 32. Analysis solution verification table.
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147 Time-History Validation The RSVVP computer program was used to compute the Sprague-Geer metrics and ANOVA metrics using time-history data from the full-scale test (i.e., true curve) and analysis data (i.e., test curve)
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148 The Sprague-Geers metrics for the y-acceleration were good regarding both magnitude (i.e., M=6.0%) and phase (i.e., P=31.7%)
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149 Similarly, the pitch angle magnitude was comparatively less than that for the yaw and roll channels (refer to Figure 99, Figure 100 and Figure 101)
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150 Table 34. Roadside safety validation metrics rating table – (multi-channel option)
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151 Table 35. Report 350 crash test criteria with the applicable test numbers.
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152 Table 36. Roadside safety phenomena importance ranking table (structural adequacy)
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153 Table 37. Roadside safety phenomena importance ranking table (occupant risk)
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154 Table 38. Roadside safety phenomena importance ranking table (vehicle trajectory)
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