On the seismic performance of straight integral abutment bridges: From advanced numerical modelling to a practice‐oriented analysis method

Abstract

The seismic performance of integral abutment bridges (IABs) is affected by the interaction with the surrounding soil, and specifically by the development of interaction forces in the embankment‐abutment and soil‐piles systems. In principle, these effects could be evaluated by means of highly demanding numerical computations that, however, can be carried out only for detailed studies of specific cases. By contrast, a low‐demanding analysis method is needed for a design‐oriented assessment of the longitudinal seismic performance of IABs. To this purpose, the present paper describes a design technique in which the frequency‐ and amplitude‐dependency of the soil‐structure interaction is modelled in a simplified manner. Specifically, the method consists of a time‐domain analysis of a simplified soil‐bridge model, in which soil‐structure interaction is simulated by means of distributed nonlinear springs connecting a free‐field ground response analysis model to the structural system. The results of this simplified method are validated against the results of advanced numerical analyses, considering different seismic scenarios. In its present state of development, the proposed simplified nonlinear model can be used for an efficient evaluation of the longitudinal response of straight IABs and can constitute a starting point for a prospective generalisation to three‐dimensional response.

A multiaxial inertial macroelement for bridge abutments

“…Under dynamic conditions, an abutment exhibits a marked frequency‐dependent response: the abutment displacements magnify in correspondence of the dominant periods of the soil–abutment system, due to the inertial effects developing in the surrounding soil, causing the transmission of relevant forces to the bridge superstructure 1,3,5,16 …”

“…Under dynamic conditions, an abutment exhibits a marked frequency-dependent response: the abutment displacements magnify in correspondence of the dominant periods of the soil-abutment system, due to the inertial effects developing in the surrounding soil, causing the transmission of relevant forces to the bridge superstructure. 1,3,5,16 In the proposed macroelement approach, these inertial effects are simulated by combining the SAME with additional masses, m i , representing the participating masses of the soil-abutment system for each loading direction. In a dynamic analysis, these masses interact with the activated plastic flows.…”

“…The magnitude of these irreversible effects depends on the flow rule of the constitutive laws used in the two models, whose main features were discussed in Section 3.1. As a result of a systematic comparison between the PDMY response and experimental data at the soil element scale and examining the dynamic response of fully coupled and reduced-order soil-bridge models, 11,16,26 it was seen that the PDMY soil model tends to overestimate the plastic volumetric strains produced by deviatoric stress component. This is the main reason why the CC model generates significant permanent settlements of the abutment.…”

Seismic reliability of Italian code‐conforming bridges

“…Due to the lack of specific provisions in the Italian code for integral bridges, in accordance with the latest draft of the second‐generation Eurocode 8 Part 2, 32 seismic design was based on a seismic analysis of a simplified numerical representation of the soil‐bridge system, with reference to an iterative linear method in which the soil‐abutment contact pressures are a function of the abutment displacement 33 . Note that traffic and seismic analyses were carried out after modelling the effective construction sequence, as a nonlinear staged construction in Sap 2000.…”

“…In the case of integral abutment overpasses, the contact between the flexible abutment and the soil is modelled with a nonlinear Winkler approach 73,74 . More details can be found in Franchin et al 22 …”