Dynamic Modeling And Field Testing Of Steel Railway Bridges

In United State, there are a lot of steel railway bridges with non-ballast tracks, which have short and simply supported spans. The majority of similar bridges on the passenger rail systems were built prior to World War II. In New Jersey, freight railcars often utilize a portion of passenger rail systems to complete their trips. Recent increases in railcar weight limits from 263,000 lb to 286,000 lb raised concerns about the passenger rail systems since these bridges were not designed according to the increased railcar weight. Also, the cost to build and maintain new bridges is extremely high. Therefore, impact of the increased railcar weight on those bridges need to be evaluated first to allow the use of passenger lines for the freight travels. The research approach adopted is aiming at evaluating current load-carrying capacity of various types of bridges to provide recommendations for dynamic impact. The impact factor equations specified in AREMA Specifications were based on field tests prior to 1960s. It is important to validate and evaluate the impact factor equation from recent field tests. In this thesis, a 2D dynamic model of train-bridge interaction system was developed. Steel bridge is simulated as a Bernoulli-Euler beam and moving train is modeled as rigid-body. Field measurement was conducted to obtain the strain, deflection, and velocity response of bridge girders under moving trains via wireless Structural Testing System (STS) and non-contact Laser Doppler Vibrometer (LDV). The validity of the presented model was confirmed through comparison with the measured structural response. Impact factor (IF) was then obtained from the validated dynamic model. Train speed, train type, bridge span length, and girder stiffness were considered as the main parameters affecting the IF. The results of this study show that the present AREMA Specifications has a tendency to overestimate the IF at speeds lower than 60 mph for steel bridges.