Damping Assessment of Bridges for Performance Base Design

Abstract

Modern performance bridge design relies on reaching controlled stages of damage and failure modes to ensure both safety and economy. In high seismic zones, the design philosophy should be based on the ability of a bridge to deform inelastically and ductilely, allowing some damage to fused elements to decrease the potential internal forces during earthquakes. This approach, however, requires a careful determination of the potential damping expected to occur on the structure and foundation. In the case of single-span or two-span bridges, the abutments have a significant impact on the bridge's performance, mainly in the longitudinal vibration modes, so the determination of the damping in the abutment is critical. In most reference bridge design manuals, the recommended damping values for abutments usually range from 5% to 10%, which results in a more robust design of the structure due to the limited allowance of energy dissipation. In particular, this paper presents a numerical study of the energy dissipation available in the abutments of common bridge typologies. The observed damage patterns in bridges near the epicentral zone induced by recent subduction earthquakes in Mexico were analyzed using 3D finite difference models. To simulate the development of damping in the abutment, a fully nonlinear approach was adopted, where the hysteretic model Sig3 coupled with the Mohr-Couomb constitutive model was considered for the mechanical and dynamic behaviour. From the results gathered in here, the relationship between damping and abutment displacements was established, and it is clearly demonstrated that the inclusion of large damping values during bridge design can lead to both cost-efficient and safe designs if a good abutment deformation assessment is conducted.