A Methodology for Modelling the Integral Abutment Behaviour of Non-Symmetrically Loaded Bridges

Abstract

Integral abutment bridges (IABs) are an economical option to design appealing single-span bridges. However, more experience is needed, as the main difference in the design of IAB compared with conventional bridges is the restraint of the frame corner, caused by the fact that the superstructure and the abutments are one monolithic structure. This requires modification in design regarding the internal forces and deformations as well as the detailing of the frame corner itself.IABs are generally designed as frames using grid models with idealised superstructure. This calculation involves sophisticated models and is considered to be time consuming. Also conventional single-spa n bridges are designed with the help of grid models, for which experience and various design software tools exist, especially when simply supported structures are considered.Main problem in the transfer of frame systems into simply supported structures are the interactions between superstructure and sub-structure. By separating the superstructure from the sub-structure, the implementation of IAB design through existing software tools is possible. However, to take into account the superstructure–abutment interaction, the superstructure needs to be restrained by rotational springs. As a result of sway effects in the original frame, the boundary conditions (horizontal position of the frame corner) for the determination of the rotational spring stiffness vary. Therefore these springs have to be non-linear, and do not comply with the demand for load case superposition.This paper presents a new approach to separate the superstructure from the sub-structure with provision for possible superposition of the load cases. The approach is based on the division of the non-linear springs into two linear springs, one for symmetric loading and the other for antimetric loading, from which a modification factor kmgk has been derived. This factor is defined as adjusting the single-span model with a single rotational linear spring to the original grid model system. On the basis of this approach and the kmgk factor, the use of conventional design tools for IABs has been made possible.To further close the gap in experience on IAB, design and detailing recommendations are given.