Passive seismic control of cable‐stayed bridges with damped resonant appendages

Abstract

SUMMARYA study is conducted to investigate the effectiveness of attaching to cable-stayed bridges resonant appendages with a relatively small mass and a high damping ratio as a means to reduce their response to earthquake excitations. The study is based on a previously developed formulation that shows that the use of these appendages may increase the inherent damping of building structures and, as a result, may reduce their response to seismic disturbances. It includes numerical and experimental tests that are conducted to assess the validity of such a formulation for the case of cable-stayed bridges and the extent to which such appendages can reduce their seismic response. In the numerical study, an actual cablestayed bridge is modelled with finite elements and analysed with and without the proposed appendages under different earthquake ground motions. Appendages with damping ratios of 10,15,20 and 30 per cent and masses that, respectively, represent 0.67, 15,2.7 and 6.0 per cent of the total mass of the bridge are considered. In the experimental test, a 3.7 m long cable-stayed bridge and an appendage consisting of a small mass, a small spring and a small viscous damper are built and the bridge tested, without and with the appendage, on a pair of shaking tables which are set to reproduce ground acceleration records from past earthquakes. The damping ratio of the appendage in this test is 32 per cent and its mass represents about 8 per cent of the total mass of the bridge model. In the numerical test, it is found that the appendages reduce the longitudinal response of the bridge deck up to 88 per cent. Similarly, in the experimental test it is found that the appendage reduces the longitudinal bridge deck response by about 41 per cent. From these studies, it is concluded that the suggested appendages may indeed be effective in reducing the seismic response of cable-stayed bridges as they are for building structures.

VIBRATION CONTROL IDENTIFICATION OF SEISMICALLY EXCITED m.d.o.f. STRUCTURE-PTMD SYSTEMS

“…For example, Xu and Kwok [18] found that the e$cacy of PTMD was not as good as expected based on a wind tunnel test of a tall building subjected to along, cross and torque wind excitations. Villaverde [19] investigated the PTMD e!ectiveness through three di!erent structures subjected to nine actual earthquake records. He found that PTMD had good performance in some cases, but some had little or even no e!ect.…”

Tuned mass dampers for response control of torsional buildings

“…Without scrutinizing the details of these studies, it is not straightforward to identify the precise reason (or reasons) for these con icting conclusions. However, Villaverde and his associate [10][11][12] o er, perhaps, the most convincing argument for these di erent ÿndings. They observe that the primary reason for ine ectiveness of the dampers is the use of the classical solutions that are not necessarily optimal for the particular situation under study.…”

The Concept and Development of Smart Structures Technologies for Long-span Cable-supported Bridges

“…However, lack of knowledge exists in the control of very flexible bridge structures which generally exhibit a complex dynamic behavior during wind and earthquakes. In deed, structural control of flexible long-span bridge structures such as cablestayed bridges has recently attracted so much interest among researchers around the world (e.g., Achkire 1997; Ali and Abdel-Ghaffar 1994; Betti and Testa 1995;Preumont et al 1999;Ni et al 2001b;Shoureshi and Bell 1996;Villaverde and Martin 1995;Wesolowsky and Wilson 2003;Wilde and Fujino 1998) that a benchmark structural control problem (Dyke et al 2000) has been proposed for cable-stayed bridge studies by a task group of the American Society of Civil Engineers (ASCE). The benchmark problem, which is a 3-d linear evaluation model, is based on a cable-stayed bridge located in Missouri, USA.…”