Finite-Element Analysis of Reinforced-Concrete Box Girder Bridges under Close-In Detonations

Abstract

Localized spalling/cratering of concrete structures subjected to close-in detonations may lead to global structural failure. This paper presents the details and results of a numerical study conducted on posttensioned concrete box girder bridges under close-in detonations. A bomb explosion within or near the bridge deck may cause catastrophic damage to the bridge components. Blast causes highly dynamic loads much larger than the conventional design loads applied relatively locally. In contrast to the bridge superstructure, significant research has been performed on the response and retrofit of buildings under blast loads. The published research on the response prediction and protection of bridges under near-field blast loads are limited. This study focuses on the evaluation and assessment of box girder bridges under blast loads. The objective of this research is to develop a reliable numerical model to predict the damage (spalling/cratering) size in a concrete deck under blast loading and the corresponding dynamic response of the damaged bridge system. The key parameters evaluated were the charge weight, charge location, and concrete deck properties. The results of this study make finite-element (FE) modeling an attractive alternative when blast testing is not feasible such as in the case of bridges. The numerical model was verified using close-in detonations on concrete slabs. Verification of the numerical model results using blast field testing on bridge systems is still necessary before this study can be expanded for additional parametric studies and comprehensive design recommendations. The damage sizes of the RC box girder bridges were predicted and assessed using a nonlinear dynamic FE code. Nonlinear regression analyses were conducted and an equation to predict the damage size depending on the scaled distance was introduced.