Approximation Of Blast Loading And Single Degree-of-freedom Modelling Parameters For Long Span Girders
Free (open access)
J. C. Gannon, K. A. Marchand & E. B. Williamson
In this paper, the modelling of long-span girders under blast loads is presented. Specifically, spans in the range of 80–160 feet, on the order of those used for typical highway girder bridges, are considered. Topics addressed in this paper include (1) applicability of a uniform equivalent load to model blasts acting on long spans, (2) mathematical development of resistance functions and dynamic transformation factors for beams subjected to multiple distributed loads, and (3) comparisons of dynamic single degree-of-freedom analyses using both a work-equivalent uniform load and an approximation using three distributed loads of variable lengths relative to a detailed representation of the blast load profile as a function of position and time using finite element analyses. Analytical studies showing the sensitivity of the results to variations in the assumptions used to determine the magnitude and length of the loading pattern are provided. Based on these studies, a new method for approximating the response of long-span girders subjected to blasts with small scaled standoffs is proposed, which differs from the equivalent uniform load approach that is typically utilized. The new method is used to carry out parametric studies of bridge superstructure response predictions as part of research work performed for a state pool-funded bridge security project and an NCHRP project involving blast-resistant bridges. Keywords: blast load, uniform equivalent load, distributed load, bridge girder, single degree-of-freedom, SDOF, load-mass factor, bridge loading, long span.
blast load, uniform equivalent load, distributed load, bridge girder, single degree-of-freedom, SDOF, load-mass factor, bridge loading, long span.