Effectiveness of basalt FRP tendons for strengthening of RC beams through the external prestressing technique

Abstract

This paper investigates the feasibility of newly developed basalt fiber reinforced polymer (BFRP) as prestressing material and the structural behavior of reinforced concrete (RC) beams strengthened with externally prestressing BFRP tendons. Three main factors potential controlling structural strengthening effects, including tension stresses, bending angles and anchorages of the tendons, were first discussed based on literature review and finite element (FE) simulation. In the structural experiment, the effects of tension stresses and the tendon profiles on the flexural behavior of RC beams were discussed and the evaluation on the ultimate bearing capacity, cracking moment, crack width and deflection of strengthened beams was conducted by theoretical calculation and experimental results. The results show that the prestressing level of BFRP tendon can be determined to be 0.50f_u and 0.38f_u (f_u is the tensile strength) according to creep rupture limit. The bending angle at the deviator is optimized to be 2° and the bond anchorage with resin epoxy was adopted to maximize strength utilization. For strengthening behavior, the second-order effect of the externally prestressed beam can be effectively relieved by using proper deviators, which is demonstrated by enhanced ultimate capacity. All of the strengthened RC beams are failed by concrete crushing, with satisfactory crack patterns and superior ductility compared to the control beam, which demonstrates the simultaneous working of internal steel reinforcements and external prestressing BFRP tendons during loading. The evaluation on mechanical behavior of strengthened RC beams indicates theoretical calculation according to several existing standards can well predict strengthening effect.