Experimental investigation and seismic vulnerability assessment of low flexural strength rectangular bridge piers retrofitted with ultrahigh-performance concrete jackets

Abstract

Effectiveness of an innovative retrofitting technique using ultrahigh-performance concrete (UHPC) jackets was investigated, for “as-built” bridge piers with low flexural strength. Cyclic loading test was performed on the pier specimens, two of which were retrofitted with a mono-wide-strip UHPC (W-UHPC) jacket, and the other two were with a multi-narrow-strip UHPC (N-UHPC) jacket. Their seismic responses were compared, regarding damage evolution, hysteretic behavior, skeleton curve, ductility and energy dissipation. The piers with the W-UHPC jacket exhibited a higher lateral strength, but were prone to plastic hinge relocation. Comparatively, N-UHPC jacket improved the piers’ ductility and smeared concrete damage. Nevertheless, guaranteeing the tight contact between the N-UHPC jacket and the shaft was crucial. Both W- and N- UHPC jackets mitigated residual drift and concrete damage, and thereby enhancing the piers’ seismic resilience. Four enhancing mechanisms from the UHPC jackets are discussed, namely passive confinement effect, cross-section enlargement effect, gap-opening effect, and interface-opening effect. Alongside, 3D solid and 1D fiber-based finite element (FE) models are constructed to represent the piers’ nonlinear static push-over (SPO) and cyclic responses, respectively. Finally, seismic vulnerability of the retrofitted piers was evaluated by generating structure-specific fragility curves.