Effect of Vehicle-Parapet Collision Forces on Bridge Girders, Bracings, and Support Bearings

Abstract

To account for the load effect due to vehicle collision with the parapet, the American Association of State Highway and Transportation Officials (AASHTO) Bridge Design Specifications contain provisions that ensure structural safety of the parapet and overhang portion of the deck slab. However, AASHTO does not consider the effect of such force on the girders, cross bracings, and supports. Lack of available literature on the subject necessitates the need to investigate the effect of this action on the structural elements that are part of the load path. In this investigation, parametric studies utilizing the finite element method on typical short and medium span composite steel girder bridges subjected to loads on the parapet are conducted. The variables that are addressed in the analysis are the length of parapet segments along the bridge, deck slab thickness, height of parapet, bridge span length, slab overhang width, number of girders, span continuity, and presence/spacing/configuration of bracings. Two types of static structural analyses are conducted, linearly elastic and nonlinear. Findings of the study showed that the bridge response obtained through 3D finite element analysis is complex in nature due to distortion induced by unsymmetrical loads and support conditions. Vertical loads due to vehicle-parapet impact forces affect the flexural stresses in the exterior girders much more than the interior girders, particularly for bridges that have few girders and are not adequately braced. The spacing of bracings and slab thickness highly impact the internal forces developed in bracing members as a result of vertical and lateral loads. The reaction components at the supports are mainly affected by the number of girders, overhang width, and span length. Structural behaviour of bridges that have adequately braced steel girders is much different than that of bridges without bracing, irrespective of the direction of the applied load on the parapet. Consideration of material nonlinearity in the analysis has little impact on the results, especially with respect to the flexural girder distribution factors and support reactions. Currently available simple approaches for analysing load effects in bridges, such as the concepts of girder distribution factor and rigid body rotation, can be useful tools for predicting bridge behaviour when subjected to load on the parapet if implemented with some modifications.