LAUSR

Abstract Integral Abutment Bridges (IABs) are robust structures without joints and bearings, hence they are less vulnerable to natural and manmade hazards, whilst they require minimal maintenance throughout their lifespan. As a result of these engineering advantages, IABs are appealing to road and railway agencies and consultants. Despite their advantages, IAB design and construction is challenging and the main barriers for extensive use of IABs originate from the interaction between the abutment and the backfill soil. This interaction causes permanent deflections of the backfill soil and enhanced soil pressures on the abutment of passive nature. Under strong earthquake excitations, the response of IABs is strongly affected by the aforementioned interaction. Surprisingly, no agreement has been reached to date in the international literature as to whether this is a beneficial or a detrimental effect. The reasons for acknowledged disagreements in the literature indicates a conceptual gap in IAB design and assessment and it, therefore, requires further investigation. To the best of the author's knowledge, the significance of this interaction in earthquake resistant IABs is dependent on a number of factors, such as the type and intensity of the earthquake, the type, length and condition of the bridge after a number of years of service, the type and height of the abutment, the bridge dynamic characteristics, e.g. stiffness, damping, mass and the type of the backfill soil, among others. Many of these competing and clashing, factors lead to worse or better IAB responses, and this depends on the additional inertia mass of the backfill soil, the additional input motion exerted on the bridge from dual paths e.g. the foundation of the abutment and the backfill soil, the dissipation capacity and stiffness of the abutment and backfill soil. With the aim of better understanding the seismic response of IABs and opine with regard to the importance of the abutment and backfill soil on the seismic response of IABs, a comprehensive state of the art review is conducted in this paper. The review includes all the aspects relevant to the IAB-backfill interaction, with emphasis on IABs subjected to earthquake excitations. The research-based evidence provided here postulates a very complex interaction effect, which may have a positive or negative effect on IAB seismic responses. The evidence gathered also suggests a minimal understanding of the potential benefits of the IAB-backfill interaction, yet a reasonable understanding of the aggravated seismic response due to the same interaction in other instances. The paper includes literature-based evidence and inferences on IAB seismic designs and concludes with the results of an extended numerical study, which was conducted to provide further evidence with regard to the effect of the bridge-backfill interaction on the seismic response and design of IABs. A representative IAB was utilised as the base model and a comprehensive parametric study was conducted varying the abutment type and height, the bridge length and the backfill soil properties. The results are evidence that, indeed, the backfill soil predominantly benefits the bridge as it reduces its bending moments and pier drifts, and which potentially can lead to more economic designs. However, the IAB-backfill interaction is strongly case-dependent and therefore meticulous and detailed modelling of the backfill soil is believed to be important to avoid underestimation of bridge stress resultants and consequent under-designs.