The following dissertation presents the initial stages of the development of the new rollover safety assessment protocol developed for paratransit buses. Each year, the State of Florida purchases over 300 paratransit buses. In 2011, the purchased buses came with over 40 different floor/wheelbase/chassis configurations. Such variety of purchased vehicles gives the ordering agencies a flexibility of ordering vehicles optimized for desired purpose, but also creates a challenge for the rollover safety assessment procedures.
Currently, there are two standards available to be used for rollover crashworthiness assessment of buses, the FMVSS 220 standard and the UN-ECE Regulation 66. The FMVSS 220 is commonly used in the United States to evaluate rollover crashworthiness of wide variety of buses. Its quasistatic nature offers an attractive, easy to perform test that provides good repeatability of results. Nevertheless, due to the nature of applied load, this procedure may not be the best choice for evaluating the dynamic behavior of a bus during a rollover accident. In contrast, the UN-ECE Regulation 66 employs a full scale, dynamic rollover test to examine response of buses in rollover accidents. The dynamic rollover, which forms the basis of the ECE-R66 approval procedure closely resembles the real world rollover accident and this regulation has been adopted by over 40 countries in the world. However, the dynamic nature of this test makes it expensive, time consuming and difficult to perform.
This situation calls for an update of an approval procedure, in order to test the purchased buses within the available time and budget. The initial development of the new assessment protocol, the Equivalent Rollover Testing (ERT) procedure, was carried out in this dissertation. The ERT procedure is conceived as an alternative approval method for the experimental or virtual full scale rollover testing. The new protocol was developed based on collected experimental experience, extensive numerical studies and theoretical considerations. The ERT procedure establishes a set of experimental tests, on the components of bus structure, that if satisfied give a high level of confidence that the tested bus will pass the requirements of the ECE-R66 rollover procedure.
The proposed ERT procedure is further tested through the parametric studies on five detailed finite element models of paratransit buses. The models, developed in the Crashworthiness and Impact Analysis Laboratory (CIAL), cover a wide range of buses, from small 138 in to a large 255 in wheelbase configurations. Through the modifications of structural components of each of the buses, a set of 132 bus designs and corresponding 132 rollover tests was established. Each of the developed buses was also subjected to the provisions of the ERT procedure. The comparison of results showed that ERT procedure presents a conservative approach to paratransit bus safety evaluation. Out of all 132 test cases there was not a single bus that passed the provisions of the ERT procedure, but has failed the full scale ECE-R66 rollover test. The proposed ERT procedure, complemented by future validation experimental study presents a promising alternative for the paratransit bus rollover safety evaluation.
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