Deflection and thickness threshold of high-strength strain-hardening cementitious composite stay-in-place formwork for modular integrated construction

Abstract

Concrete modular integrated construction (MiC) involves stay-in-place (SIP) wall formwork during construction, which is subjected to lateral pressure from cast-in-situ fresh concrete and is usually thick and heavily reinforced to limit deflection and cracking. Strain-hardening cementitious composite (SHCC) with strain-hardening and multiple cracking behaviors could significantly reduce the wall thickness. However, the maximum deflection and thickness threshold of SHCC wall formwork under casting loads are unknown. In this paper, the bending tests of half-scale SHCC plates with varying thicknesses, reinforcement layouts, and boundary conditions were first performed. Due to the fiber-bridging behavior, numerous micro-cracks appeared on the plate surfaces and the SHCC plates presented excellent bending ductility. Placing transverse rebars close to the outer surface, increasing plate thickness, and enhancing boundaries could effectively delay the cracking. Subsequently, a refined finite element (FE) model for the bending test was built and validated by the test results. 128 FE models were calculated to investigate the effects of plate thickness, plate widths, and reinforcement ratios. The maximum deflection increased with plate widths, indicating that a wider wall formwork required a larger thickness. Finally, the deflection calculation procedure of SHCC wall formwork was proposed based on the calculus of variations and the Galerkin method. The thickness thresholds of SHCC wall formwork with the widths of 1000, 1500, 2000, and 2500 mm are 50, 60, 70, and 80 mm, respectively.