Verification, validation and optimization of finite element model of bus structure for rollover test

Paratransit buses consist of a custom body mounted to a GM/Ford cutaway chassis by a secondary manufacturer called body builder. Paratransit buses form a significant segment of the bus market in the US nowadays. They are used as a complementary service for regularly scheduled routes and usually are prepared to transport disabled passengers in their wheelchairs. Their construction method and the lack of applicable national crashworthiness standards result in a wide variance of passenger compartment structural strength amongst manufactures---as reported by the Florida Department of Transportation (FDOT). The primary objective of this dissertation was to develop a testing procedure with the performance rating system for paratransit buses acquired by the state of Florida. Sponsored by FDOT an assessment and improvement methodology was developed using joint computational and empirical approach. It prioritizes the strength of the structure in a rollover type accident utilizing as a basis the European Regulation ECE-R66. New measure of safety margin in rollover tests, a Deformation Index, was proposed. Detailed Finite Element (FE) model of selected paratransit bus was developed and used to perform explicit LS-DYNA simulations of the tilt table rollover test. Experimental tests on the bus subsections were conducted for validation purposes and weak spot identification. Discrete optimization using the Successive Response Surface Methodology in LS-OPT was also utilized to indentify parts of the structure critical to rollover performance. Improvements were suggested that minimize the addition of mass. Early results showed the connections between major structural components (floor/wall/roof) to be particularly weak. Proposed structural modifications increased the remaining safety margin from an initial level of 16% to 29% (In respect to the Deformation Index). The structural modifications resulting from the validation testing were incorporated in the currently produced buses. The proposed testing procedure was accepted by FDOT in August 2007 as the Crash and Safety Assessment Program. It received attention of the state and federal transportation agencies and support from the transit bus industry.