Spatial Variation of Stiffness and Edge Beam Participation in RC Box Culverts

Abstract

Reinforced concrete (RC) box culverts exhibit a non-uniform structural response under two patch localized loading due to plate action and boundary elements at the opening that are not accounted for in conventional 2-D models for design and analysis purposes. This paper addresses the spatial variation in the stiffness of RC box culverts with and without edge beams, using linear-elastic finite-element analysis. Stiffness was derived from the load-deflection responses at various locations along the culvert length. The results show that the stiffness depends on the load location, indicating that the culvert system does not behave as a uniform structural element. The presence of the edge beam leads to local stiffness amplification near the opening, which gradually diminishes towards midspan. The reaction distributions also indicate that the edge beam acts primarily as a boundary stiffener and that the global load-transfer mechanism remains unchanged. The contribution of the edge beam was isolated using a relative stiffness parameter that exhibits a consistent exponential-decay trend across different spans. Based on these observations, a span sensitive formulation was developed to describe this behavior as a function of distance, and it showed good agreement with finite-element results (R2 = 0.979). The proposed framework offers a physically interpretable representation of edge-beam stiffness participation in an indeterminate structure and adds to a better understanding of the load distribution behavior in the culvert with and without edge beams.