۱- Introduction

۲- Bridge model

۳- Test protocol

۴- Test results and discussion

۵- Numerical modeling and validation

۶- Conclusions

References

Abstract

In current transverse seismic design of long span cable-stayed bridges, the conventional transverse fixed system (TFS) is usually adopted. This strategy inevitably increases seismic demands of substructures and towers, leading to high seismic-induced damage risks to the bridges. To address this issue, the authors recently developed a novel Transverse Steel Damper (TSD) and correspondingly proposed an innovative TSD seismic system (TSDSS), in which the TSDs were placed at deck-tower and/or deck-bent connections. To further verify the reliability and seismic isolation efficiency of TSDSS for long span cable-stayed bridges under near- and far-fault ground motions, a series of experiments on a 1/35-scale model of a kilometer-span cable-stayed bridge were conducted on a four-shake-table testing system. Experimental results indicate that (1) compared with the conventional TFS, the TSDSS can reduce transverse displacement and curvature demands along bent/tower columns, meanwhile limiting displacements at deck-bent/tower connections to an acceptable level in engineering practice. (2) The sensitivity of TSDSS to ground motions is obviously lower than that of the conventional TFS. The isolation efficiency of TSDSS is robust regardless under near- or far-fault ground motions; (3) Increasing the yield strength of TSDs can decrease the relative displacements at deck-bent/tower connections. In general, the TSDSS is experimentally validated to be a capable and reliable strategy for the seismic design of long span cable-stayed bridges. Additionally, the shake-table test is simulated using a finite element model, which provides good agreements with the test results.

Introduction

In the last three decades, a large number of cable-stayed bridges have been constructed in China. These bridges usually serve as key joints in national or local transport networks. Considering the importance of these bridges in networks and to ensure the essential postearthquake functionality, the main structural components of cablestayed bridges, including towers, foundations and superstructures, are required to remain elastic under design-level earthquakes with a return period of 2000 years in Chinese seismic design specifications [1,2]. However, severe damages were still detected in cable-stayed bridges during some recent strong earthquakes. For example, in 1999 Chi-Chi, Taiwan earthquake, Chi-Lu Bridge suffered severe damages in the towers [3]. Therefore, how to improve the seismic performances of cable-stayed bridges has drawn increasing attentions from both the engineering and academic community. In the longitudinal direction, a full- or semi-floating system is often applied in practice. In such a system, Fluid Viscous Dampers (FVDs) [4–۷] are often installed at decktower connections to reduce shear and bending demands at tower bottoms and foundations, meanwhile limiting relative displacements between deck and towers to a practically acceptable level. In this manner, longitudinal seismic performances of cable-stayed bridges are generally acceptable for practice. In the transverse direction, however, rigid constraints are often adopted at deck-bent/tower connections for providing enough stiffness to carry traffic and wind loads under service conditions [8]. This is the so-called conventional Transverse Fixed System (TFS), which inevitably increases seismic demands at bents (or piers), towers and foundations. To meet the seismic design requirements, these components are always designed, in an uneconomic manner, with sufficient strength capacity to resist design-level earthquakes. In this regard, transversal isolation systems for cable-stayed bridges, especially in high seismic regions, are highly demanded.