Seismic behavior of BFRP bar reinforced shear walls strengthened with ultra-high-performance concrete boundary elements

Abstract

Reducing the amount of steel reinforcement in construction is imperative, driven by the objectives of reducing carbon emissions and mitigating steel corrosion. Among the various alternatives to steel reinforcement, basalt fiber reinforced polymer bar (BFRP) is considered a promising solution. The aim of this study is to examine the seismic performance of shear walls entirely reinforced with BFRP bars, utilizing BFRP for both longitudinal and transverse reinforcement. To address the inherent limitations of BFRP bars, a novel composite shear wall, incorporating BFRP bars, ultra-high-performance concrete (UHPC) and normal strength concrete, is proposed. Specifically, UHPC boundary elements are employed to strengthen the potential compression zone of BFRP reinforced shear walls. Four shear wall specimens, fully reinforced with BFRP bars, were fabricated and tested for their seismic performance, with two specimens incorporating UHPC boundary elements. Comprehensive test results, including failure modes, load-bearing capacity, ductility, energy dissipation, stiffness degradation and rebar strain, are presented and discussed. A detailed discussion of the effects of axial load ratio (ALR) and UHPC boundary elements is included. The test results indicate that the specimens featuring UHPC boundary elements showed significant improvements in deformability, lateral strength and energy dissipation capacity. This reveals that the integration of UHPC boundary elements considerably enhances the seismic performance of BFRP bar reinforced shear walls. Moreover, although all test specimens experienced failure due to concrete crushing in the compression zone, those with UHPC boundary elements manifested higher tensile strain on the BFRP bars on the tension side, facilitating more effective utilization of the high tensile strength of the BFRP bars. Ultimately, a method to ascertain the flexural capacity of BFRP bar reinforced shear walls, both with and without UHPC boundary elements, is proposed and validated by the test results.