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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11 2 STATE OF PRACTICE FOR BARRIERS AND MSE WALLS This chapter includes background regarding MSE wall design and construction methods, design practice of roadside barriers, roadside barrier crash testing criteria, and design of barriers atop of MSE walls. 2.1 Design of Mechanically Stabilized Earth Wall System MSE walls are composed of three major elements: soil, reinforcing elements, and facing.
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12 - The slope stability design ensures that there is only a very low probability of generating a deep seated rotation failure.
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13 Note: From AASHTO LRFD Bridge Design Specifications, 2014, by the American Association of State Highway and Transportation Officials, Washington, D.C. Used with permission.
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14 Additional information regarding the external and internal stability analysis of MSE wall is presented in AASHTO LRFD. Note: From AASHTO LRFD Bridge Design Specifications, 2014, by the American Association of State Highway and Transportation Officials, Washington, D.C.
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15 2.1.2 LRFD vs. ASD Design Approach MSE walls are being designed on the basis of the LRFD approach.
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16 Table 2-1 Comparison between LRFD factors and ASD factors for designing MSE wall.
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17 2.2 Design and Evaluation of Longitudinal Barrier and Bridge Rails This section includes background regarding roadside barrier design and crash testing criteria, analyses of crash test data for TL-4 and TL-5 impacts, and a history of design loads for heavy trucks. 2.2.1 Guidelines for Barrier Evaluation Guidelines for testing and evaluation of roadside barriers systems started in 1962 with Highway Research Circular 482 entitled "Proposed Full-Scale Testing Procedures for Guardrails" (12)
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18 These changes increased the IS, or lateral kinetic energy of the test vehicle, by 56%. Table 2-2 Vehicle description incorporated in NCHRP Report 350 and MASH (4-5)
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19 design of bridge rails following ASD design procedures. This finding does not necessarily mean that railings designed for a static load of 10 kips (44.5 kN)
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20 a) Analyses within wall segment b)
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21 Numerous TL-4 full-scale crash tests were conducted in accordance with NCHRP Report 350 specifications. A rail height of 32 in.
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22 (36,288 kg)
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23 Table 2-4 summarizes the impact conditions, maximum 50-msec. average lateral acceleration and barrier geometry associated with the large truck crash tests reviewed as part of this study.
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24 Table 2-4 Summary of full-scale crash test conducted with tractor-trailer vehicles Test No. / Agency/ Ref.
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26 approximately 110 kips (489.3 kN) and 168 kips (747.3 kN)
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27 Each segment of the wall was instrumented with four strain gage load cells and one accelerometer located at its CG. The outputs derived from this instrumentation were used to compute the magnitude and location of the impact force using principals of structural dynamics.
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28 Table 2-5 Summary of the instrumented wall test program with tractor-trailers (13)
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29 Figure 2-8 50-msec. average acceleration impact force-Test 7046-3 (13)
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30 Linear regression analyses were conducted for a selected number of large trucks crash tests based on the assumption that the lateral impact force is approximately proportional to the kinetic energy (or IS) of a given impact.
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31 will result in an overly conservative moment slab design. This is due in large measure to the barrier inertial effects that are not accounted for in the static equilibrium analysis.
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32 static load was comparable to the recommended static load presented in the AASHTO Guidelines Specification for Bridge Design (35)
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33 Data collected from the results of the barrier stability analyses and the bogie impact tests on the 5-ft (1.52 m) high MSE wall served as a basis to draft a TL-3 design guideline in AASHTO LRFD format.
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34 Figure 2-13 Barrier on MSE wall prior to testing (2)
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35 0.000 s 0.086 s 0.171 s 0.340 s General Information Test Agency ......................
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36 Table 2-6 Summary of the stability tests, bogie tests, and full-scale crash test conducted under NCHRP Project 22-20 (2)
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37 2.4.2 Design of Barriers and MSE Walls for Vehicle Impact Section 11 of the AASHTO LRFD Bridge Design Specification (3) outlines the procedure to design a barrier on top of an MSE wall.
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38 load, that is the static load equivalent to the impact dynamic load that is used in the proportioning of the moment slab, is 10 kips (44.5 kN)
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