Construction Technology for Integral Bridges with Basalt Fiber-Reinforced Polymer Prestressing Tendons

Abstract

AbstractConventional structural materials are being replaced by advanced composite materials owing to their superior mechanical properties. Basalt fiber-reinforced polymer (BFRP) is the latest fiber-reinforced polymer (FRP) composite material introduced as reinforcement and pre-stressing tendons for reinforced concrete (RC) and pre-stressed concrete (PSC) structures. On the other hand, with the increasing demand on flyovers and bridges in city spaces, planning and design must address faster constructions of aesthetically appealing slender bridges, which are making joint-less, i.e., integral bridges popular. Therefore, beginning from designing the components required for the use of the BFRP in pre-stressing operations to establishing design procedure of the BFRP-PSC members of integral bridges are required. Evaluating mechanical properties of the BFRP rods/ tendons is challenging using the existing mechanical testing methods due to their relatively lower transverse direction strength. This creates issues not only in characterization of the BFRP in laboratory conditions but also on-field pre-stressing application in integral bridges. Hence, development of a proper anchor with optimum size for the BFRP rods is crucial. Hence, expansive cement grout-based anchor is developed, tested, and assessed, by studying the parameters affecting the gripping behavior and optimizing the anchor design based on the finite element (FE) analysis. Then again, understanding of the thermo-mechanical behavior of the BFRP composites is needed for practical and cost-effective applications in integral bridges, experiencing thermal stresses throughout their service-life. Characterization and assessment of performance of the BFRP rods at elevated temperatures is investigated through extensive experimental and analytical studies. Consequently, a semi-empirical constitutive law for predicting the thermo-mechanical behavior of FRP composites is proposed and validated with experimental results. The proposed model is original, generic, and flexible, and is based on typical characteristics of the composite, eliminating the requirement for conducting the tension test at elevated temperatures. Experimental investigations are carried out to assess the flexural performance of the BFRP-pre-stressed concrete (PSC) beams designed as over-reinforced, under-reinforced, and significantly under-reinforced, as well as the non-pre-stressed concrete beams, for developing design philosophy for the BFRP-reinforced/ pre-stressed concrete members. The assessment is made based on the flexural strength, serviceability satisfaction, safety factor against failure, and deformability/ ductility. The efficacy of the partial pre-stressing of the beams in a multi-layered system of tendons is investigated, and an alternative source of ductility is introduced by allowing the tendons to rupture sequentially in a progressive manner. Furthermore, the flexural analysis of the tested beams is carried out based on the available code provisions for complimenting the experimental findings. Ductility evaluation of concrete beams pre-stressed with the FRP tendons is conducted, wherein the effect of the partial pre-stressing, layering of the tendons, addition of sacrificial rebars, and functionally-graded concrete (FGC) is elaborated. The finite element analysis (FEA) testified the efficacy of the introduced techniques in improving the ductility of the FRP-pre-stressed members. To investigate on the efficacy of using the BFRP pre-stressing tendons in integral bridges, the BFRP tendons are used for the design of conventional and integral bridges, and a comparative assessment is carried out with steel-pre-stressed conventional bridges. It is concluded that employing both the techniques of using the non-corroding BFRP tendons and the proposed integral form of bridges is a promising technology in bridge construction. Apart from that, the natural fiber composites, being cost effective and environment-friendly, are investigated for possible use in post-tensioning of RC beams. The successful utilization of such natural fibers in structural applications may result in more sustainability in construction industry.