Dynamic Stress Amplification Caused by Sudden Failure of Tension Members in Steel Truss Bridges

The property of dynamic stress amplification resulting from the sudden failure of a tension member in a truss bridge is investigated by a precise dynamic response analysis. The primary sources of the dynamic stress amplification are from two types of impacts. The primary impact is attributable to longitudinal strain wave propagation from a failure point. The secondary impact is a result of the dynamic transition of equilibrium from a prefailure to a postfailure state. However, the effect of the primary impact is so small that it can be ignored in evaluating the impact coefficients used for the structural redundancy analysis. The impact coefficients for critical members in a structure take almost a constant value that ranges from 1.4 to 1.8, for which 5% structural damping is assumed, following the single degree of freedom model employed to evaluate the existing impact coefficient of 1.854. To avoid a cumbersome dynamic response analysis, the root mean square mode combination method is applied to calculate approximately the impact coefficients. The impact coefficients so calculated are moderately accurate for practical purposes. DOI: 10.1061/(ASCE)ST.1943-541X.0000338. (C) 2011 American Society of Civil Engineers.