Crashworthiness Evaluation of Cutaway Buses

Crashworthiness Evaluation of Cutaway Buses

The State of Florida acquires about 300 cutaway buses every year. They are used for paratransit services in all cities and counties in the state and they are also popular to transport elderly in nursing homes, youngsters for schools, passengers around airports, and others. Their structure is unique as they are made in two step process. In the first, a cutaway vehicle (consisting of a chassis and a driver cab) is made by one of the major auto manufacturers. The second stage comprises of adding a passenger compartment per customer specification.

The Transit Office of the Florida Department of Transportation (FDOT) established the Crashworthiness Evaluation of Cutaway Buses Program in 1999. The Program is located at the Crashworthiness and Impact Analysis Laboratory (CIAL) at the Florida A&M University – Florida State University joint College of Engineering in Tallahassee, Florida. Parts of the experimental Program are also carried out in Transit Research, Inspection, and Procurement Services (TRIPS) at Springhill Rd in Tallahassee, FL. The Crashworthiness Evaluation Program has a mission of using a cutting edge computational mechanics and experimentation to ensure the safest paratransit services in the State of Florida.

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CIAL research interests and expertise include applied computational mechanics and numerical analysis, non-linear, dynamic finite element methods, computer modeling, contact, impact and penetration problems, crashworthiness, safety, vulnerability and survivability, energetic materials and detonation science.

Most research projects are conducted using LS-DYNA non-linear, 3-D, dynamic, explicit finite element code. Past projects were sponsored by: the Florida Department of Transportation, National Science Foundation, Federal Highway Administration, Federal Transit Administration, Army Research Lab, Defense Threat Reduction Agency, and others.

The enthusiastic CIAL research team ranges from M.S. students to international scholars and experienced post-doctoral associates.Currently two Ph.D students Reza Seyedi and Grzegorz Dolzyk are working in the CIAL lab.

Background

Concerns about cutaway bus rollover led the Florida Department of Transportation to initiate research on crashworthiness of cutaway buses.

Rollover is a complex, dynamic event that differs from other impact (frontal, side, rear) vehicle accident types in that its likelihood of occurring is influenced greatly by the physical properties of the vehicle — in particular the vehicle’s COG location. In absence of a specific standard, most manufacturers choose to perform voluntary testing to the quasi-static FMVSS 220 School Bus roof strength standard. CIAL’s evaluation of five different manufacturers’ designs using both FE simulations and physical testing has revealed that in order pass the FMVSS 220, every manufacturer was using an unbalanced design with strong roof bows but weak columns and connections. This design performs well on the quasi-static FMVSS 220 test but will perform poorly in actual rollover accidents where side loading is present.

about1Modern dynamic testing has been adopted by forty four members of the United Nations (except the US) all over the world (UN ECE Regulation 66, February 2006). Although less repetitive than quasi-static FMVSS 220 test, the tilt table tests offer a better insight into the bus performance during its rollover accidents. Hence, the dynamic testing philosophy has been adopted for testing and crashworthiness assessment of cutaway buses purchased in Florida.

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