Experiment Investigation of Viscoelastic Low-Prestressed Self-Centering Braces

Abstract

Self-centering braces are an attractive new type of brace able to reduce structural residual deformations after earthquakes, with no requirement of major modifications to structural joints. One primary challenge in widespread implementations of self-centering braces is their high demands of prestressing forces, in order to counteract the anti-recentering resistance induced by their energy-dissipation system. This paper introduces a novel self-centering (SC) brace, denoted as a viscoelastic low-prestressing self-centering (VE-LPSC) brace, that needs only a low level of prestressing force to achieve self-centering. The proposed brace incorporates a novel frequency-independent viscoelastic damper (VED) as its energy-dissipation system. The new VED behaves similarly to displacement-based dampers that provide stable stiffness and damping across various frequencies. Meanwhile, as loading ends, the VED does not generate residual anti-recentering forces, unlike conventional velocity-based dampers. Performance tests on the VEDs were first conducted using three specimens to examine the material’s deformation capacity, frequency-independent characteristic, fatigue-resistance capacity, and recovery capacity. Then, six full-scale brace prototype specimens were manufactured and tested, considering three levels of prestressing forces (15, 50, and 100 kN). Test results revealed that the brace achieved complete self-centering and consistent stiffness and strength under various frequencies, even with a prestressing force of 15 kN. With conventional steel strand and Belleville springs as its prestressed elements, the new brace was able to elongate 2.27% (corresponding to a story drift of 4.54%) while maintaining its recentering capacity. The VE-LPSC brace may experience some strength degradation after loading lower to 90%, but its capacity can recover to 98% of the original strength after 2 weeks.