Evaluation of Bridge Rail Systems to Confirm AASHTO MASH Compliance (2022) / Chapter Skim
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3 Introduction NCHRP Report 350 contains information for evaluating the safety performance of roadside features, such as longitudinal barriers, terminals, crash cushions, and breakaway structures (1)
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4 Evaluation of Bridge Rail Systems to Confirm AASHTO MASH Compliance ratio of contact width to rail height were all evaluated according to these figures. In addition, the loading and height information as shown in AASHTO LRFD Table A13.2-1 was updated for the current MASH-2016 specifications.
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Background and Objective 5 MASH Major Changes and Implications MASH was developed to incorporate significant changes and additions to the procedures for assessing the performance of roadside safety hardware, including new design vehicles that better reflect the changing character of the vehicles using the highway network. For example, MASH increased the weight of the pickup truck design test vehicle from 4,409 to 5,000 lb., changed the body style from a ¾-ton standard cab to a ½-ton four-door cab, and imposed a minimum height for the vertical center of gravity of 28 in.
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6 Evaluation of Bridge Rail Systems to Confirm AASHTO MASH Compliance MASH. The minimum rail height for MASH TL-4 barriers was determined to be 36 in.
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Background and Objective 7 • Concrete metal combined (traffic only) – With curb ◾ Three metal members ◾ Two metal members ◾ One metal member – With parapet ◾ Three metal members ◾ Two metal members ◾ One metal member • Combination traffic-pedestrian – With sidewalk – Without sidewalk • Wood only • Noise wall only • Retrofit only The bridge rails in each category were ranked in order of weighted frequency of use (WFofU)
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8 Evaluation of Bridge Rail Systems to Confirm AASHTO MASH Compliance Table 1.1. Ranking based on WFofU per category -- survey results.
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Background and Objective 9 barrier did roll after impact with the vertical wall but was fairly stable throughout the impact event. Based on the results from the simulations, the minimum recommended rail height for MASH TL-3 bridge rails is 29 in.
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10 Evaluation of Bridge Rail Systems to Confirm AASHTO MASH Compliance to provide improved stability for heavy-truck impacts and to accommodate future pavement overlays. Although not a specific MASH evaluation criterion, consideration should be given to the potential for occupant head excursion and contact with components of the bridge rail system for these taller barriers -- testing to date has not found this to be a problem with existing rails.
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Background and Objective 11 when tested with smaller vehicles. Testing of 42-in.
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12 Evaluation of Bridge Rail Systems to Confirm AASHTO MASH Compliance to determine which rails could be considered MASH-compliant and which would require further analysis or crash testing to establish MASH compliance. Stability Requirements for MASH Bridge Rail Systems For a bridge rail system to be considered a MASH-acceptable barrier, a minimum height must be met to ensure stability of the vehicle.
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Background and Objective 13 For concrete parapet railings, the yield line method was applied by Silvestri-Dobrovolny et al. to determine the ultimate strength of the system.
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14 Evaluation of Bridge Rail Systems to Confirm AASHTO MASH Compliance MASH Test Level Recommendation Justification TL-3 29-in. minimum rail height Full-scale impact simulations performed under NCHRP Project 20-07 (7)
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Background and Objective 15 Not Satisfactory. The not satisfactory (NS)
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16 Evaluation of Bridge Rail Systems to Confirm AASHTO MASH Compliance A flow diagram of the rail-specific evaluation assessment designation process for the three evaluation criteria is presented in Figure 1.6. Overall Assessment.
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Background and Objective 17 testing was needed. If any of the three evaluation criteria was given an M or NS designation, an NS overall designation was assigned to that bridge rail system.
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18 Evaluation of Bridge Rail Systems to Confirm AASHTO MASH Compliance NCHRP Report 350 Test Level Category Subcategory System Name Evaluated MASH Test Level Stability Geometrics Strength Overall Assessment TL-4 Metal Only Deck Mounted Type A42 Metal Bridge Railing (NM) TL-4 S S S S TL-4 Combined (Traffic)
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