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134 C H A P T E R 6 Conclusions FE computer simulations were conducted to evaluate the current AASHTO LRFD Bridge Design Specifications (6) geometric figures A13.1.1-2 and A13.1.1-3. The guidance in these figures was previously based on NCHRP Report 230 and NCHRP Report 350 crash-test data. It was necessary to evaluate these figures for MASH TL-3 impact conditions. Initial computer simulations were performed on various concrete post-and-beam, deck- mounted metal post-and-beam, curb-mounted metal post-and-beam, and parapet-mounted metal post-and-beam bridge rail systems. All the systems were found to be acceptable for MASH Test 3-11 evaluation criteria. Several systems were not acceptable for MASH Test 3-10 evaluation criteria. These simulations exhibited significant interaction between the wheel and bridge rail components, which required further evaluation and validation through crash testing. Full-scale crash testing was performed on two bridge rail systems with large vertical clear openings. The tests were performed according to MASH Test 3-10 criteria. The information from the crash tests was used to validate and improve the computer simulations. In both crash tests, the vehicle wheel released from the vehicle during impact with the bridge rail post. This phenomenon was not captured in the initial computer simulations. A modified version of the 1100C small car vehicle model that included capability for wheel and suspension failures was then developed. Subsequent numerical evaluations of concrete post-and- beam, deck-mounted metal post-and-beam, curb-mounted metal post-and-beam, and parapet- mounted metal post-and-beam systems were conducted with the modified vehicle model. All bridge rail systems were found to be acceptable per MASH Test 3-10 and 3-11 evaluation criteria using the modified 1100C vehicle model. Finally, modified geometric figures were developed for possible replacement of the current AASHTO LRFD Figures A13.1.1-2 and A13.1.1-3. The proposed curves indicate a ârecommendedâ region and ânot recommendedâ region. Application of the proposed curves from a design perspective will consist of a user plotting the bridge rail geometrics on the two curves and verifying that the geometrics are in the recom- mended regions. A user can also start with a post setback distance (e.g., rail size) and select a corresponding vertical clear opening and rail contact width-to-height ratio in the recommended regions. The bridge rail dimensions can then be configured based on the post setback distance, vertical clear opening, and rail contact width-to-height ratio. Recommendations The adoption of the modified curves will provide bridge designers updated guidance on bridge rail geometrics that will comply with MASH. It is recommended that these curves be included in a future update to AASHTO LRFD Section 13. Summary
