Soil Structure Interaction of Integral Bridge Using Finite Element Method

Introduction

A type of bridge that is used extensively in road applications in particular is the integral abutment bridge (IAB). The concept of "integral abutment bridge" has recently become a topic of remarkable interest among bridge engineers, not only for newly built bridges but also during refurbishment processes. The system constituted by the substructure and the superstructure can achieve a composite action responding as a single structural unit. Integral bridges in simple words can be defined as bridges without joints. Integral bridges are characterized by monolithic connection between the deck and the substructure (piers and abutments). They span from one abutment, over intermediate support to the other abutment, without any joint in the deck.

Soil structure interaction for integral bridge.
Integral bridge is a classical example of soil-structure interaction. Although the integral bridge concept has proven to be economical in initial construction for a wide range of span lengths, as well as technically successful in eliminating expansion joint/bearing problems, it is susceptible to different problems that turn out to be geotechnical in nature. The movement of integral bridge abutments, especially due to thermal expansion and contraction of the bridge deck, can create passive and active earth soil conditions in the backfill. The soil reaction is linear and varies with depth. The earth pressure is dependent on the stiffness of the soil and the amount and nature of wall displacement, which can be translation and/or rotation. This interdependency of the nature and amount of displacements both in the soil and the structure to the stresses created at the process is the soil –structure interaction problem to be dealt with as shown in the figure below.

Passive pressure that develops behind the integral bridge abutment depends on the soil density, soil to wall friction angle, mode of wall displacement, effect of backfill confinement and repeated loading. Handling the soil structure interaction in the analysis and design of integral abutment bridges has always been problematic. Using commercially available software the nonlinear soil behavior can be handled using nonlinear springs at the abutment and piles. The nonlinear soil springs behind the abutment walls are the force deflection design curves recommended in National Cooperative Highways Research Program (NCHRP) (1991) design manual.

Advantages of integral bridges

• Elimination of expansion joints and bearings:
• Simplified substructure:
• Slender superstructure
• Drive comfort improvement
• Remove of problematic details
• Robust structure
• Resistance to pressure
• Simplified widening and replacement