Kuang-Han Chu

DYNAMIC INTERACTION OF RAILWAY TRAIN AND BRIDGES

An analytical method for obtaining the dynamic response of a train moving on a bridge is presented. The ratio of dynamic response to maximum static response is called the amplification factor, and its maximum absolute value minus one is called the impact. Each four-axle locomotive is modelled as a rigid body with three degrees of freedom: bounce, pitch, and roll, and with a suspension system consisting of springs mounted on wheels. The carriages are assumed to be connected by frictionless joints to form the train. The bridge is modelled as a three dimensional structure, with the masses lumped at the truss joints. All joints, including the floor beam connections, are assumed to be rigid, except those for the bracing members, which are assumed to be hinged. Vertical displacements are considered as the only dynamic degree of freedom. The mathematical formulation is described briefly, and a numerical example is given. Locomotive and truss member properties, together with stresses in some typical members, are given in the tables. The amplification factors of the responses in some typical bridge members are shown in the figures.

Dynamic analysis of a bulkhead flat car underframe structure

Abstract A dynamic analysis of the underframe (U/F) structure of a 100-ton bulkhead flat car was performed. Center plate accelerations and side bearing forces were obtained from the dynamic analysis of the car system using random track irregularity inputs. In this analysis the carbody was treated as two rigid elements connected by springs. The objective of this study was: (a) to investigate the effect of bulkheads on the natural frequencies and mode shapes of the U/F structure; (b) to evaluate the maximum dynamic stresses and stress ranges for a few selected critical members of the U/F structure; (c) to determine the influence of the bulkheads and structural damping, in both the original and new (statically optimized) U/F structure designs: (d) to compare the calculated dynamic stresses in a few selected members, with increased static stresses based on dynamic load factors for specified design loads; (e) to modify the design of the U/F structure according to the results of the dynamic analysis; and (f) to discuss the fatigue life of the U/F structure, based on the calculated stress ranges.