Computational simulation of eccentrically loaded reinforced concrete walls formed with modular thin-walled permanent formwork system

Stay-in-place formwork (SIPF) systems represent a conventional formwork-free, corrosion-resistant substitute for construction of new reinforced concrete walls. The composite of infill concrete and thin-walled fibre cement board (FCB)/steel studs SIPF consists of a core concrete, filled between two FCBs that are connected to each other using steel studs, embedded to the concrete infill. Similarly, the concrete-filled Polyvinyl Chloride (PVC) hybrid system is comprised of extruded PVC interlocked encasements core-filled with concrete. These lightweight structural SIPFs are utilised in modular construction in which the system is prefabricated in the factory, transported to the site, erected and assembled for concrete casting. Further, the SIPF-encased wall is a composite system that facilitates taking advantage of mixed effects of reinforced concrete and SIPF. These are the major benefits of these systems compared to conventional formwork systems. However, there is a gap in knowledge regarding the strength and ductility measurement of SIPF-encased walls under eccentric axial loads that is presented in this paper. A series of tests was conducted to failure on both composite walls and compared with the reference specimens, i.e. standard walls (STWs). Substantial finite element (FE) studies considering material and geometric nonlinearities as well as contact behaviour are also performed. After a reasonable model verification against test results, a comprehensive parametric investigation accounting for the concrete compressive strength, the thickness of SIPF components (i.e. steel studs, FCB, and PVC), longitudinal bar reinforcement, and axial load ratio is performed. Further, the experimental and numerical results are used to assess the suitability of the theoretical formulation specified in the current Australian Standard (AS3600) for the axial-flexural interaction resistance of SIPF-encased walls. It is demonstrated that the predictions from the current design specifications are overall conservative. Further, it is found that FCB/steel studs SIPF effectively contributes to improve curvature ductility index and axial-flexural strength compared to STWs.