Seismic performance of Transverse Steel Damper seismic system for long span bridges

To provide seismic resistance of long span bridges in transverse direction, fixed bearings are often installed between girders and piers (or towers). Although the fixed bearings and substructures can be designed extraordinarily strong to resist the design seismic loads, they may still be vulnerable when the design seismic loads are exceeded. To address this issue, this paper proposes a novel seismic system, which combines Transverse Steel Dampers (TSDs) with conventional sliding bearings, and is named the TSD seismic system. A TSD consists of several triangular steel plates outfitted with steel hemispheres at their upper vertices. The steel hemispheres not only allow free movements of the superstructures with respect to the piers in the longitudinal direction, but also provide reliable load paths in the transverse direction. Quasi-static tests have been conducted to investigate seismic behaviors of the TSD using two scaled and two prototype specimens. Test results show that the TSD has excellent performance in energy dissipation, large displacements, and synchronization of triangular plates under complex contact conditions. The load-displacement constitutive model of the TSD has been established using a bilinear model in ABAQUS, followed by a design method for the TSD seismic system. A 620 m long-span cable-stayed bridge was selected for a case study of the TSD seismic system. Ground motions recorded at various site conditions were used as seismic inputs. Numerical results show that: (1) the TSD seismic system can achieve a desired balance of transverse seismic displacements and forces, which is not the case when a sliding bearing system (without TSDs) or a fixed bearing system is used; (2) TSDs contribute to most of the energy dissipation capacity of a TSD seismic system while the contribution of sliding bearings is negligible; and (3) the proposed TSD seismic system, compared with a sliding system, tends to be less sensitive to seismic input properties, such as peak ground accelerations and site conditions.