Prediction Method for Response of Steel Bridge Beams and Girders to Blast and Fragment Loads

The military requires methods of predicting the response of steel bridge beams and girders to blast and fragment loads. The methods must provide quick answers to analysts who have very little experience, if any, in the blast response of structures. Similar tools also would be beneficial to transportation engineers who must evaluate bridges against terrorist events. Because data on the response of these beams to blast and fragments are extremely limited, finite element simulations were performed to create a numerical database that includes the typical range of steel bridge and girder dimensions. The simulation results were used to determine the loading characteristics that significantly affect the response. Loading characteristics were reduced to a load measure, a single number that can be easily computed for any combination of fragment and blast loads. If the load measure is exceeded for a given combination of blast and fragment loads, then beam failure is predicted. A computer code was developed to predict fragment and blast loads from conventional weapons and to determine the load measure for any given load case so an analyst with knowledge of weapon and beam geometry can easily predict whether a beam will fail. Model development and validation are presented. The model was developed to predict the response of bridge beams and girders to conventional weapons but could be extended to a model for predicting the response to terrorist weapons.