Seismic performance of PVA textile cementitious composites used as permanent formwork in full-scale circular RC columns

Abstract

The strength, stiffness and ductility capacity of structural systems must be protected under seismic effects. In the presence of lateral reinforcement, the confinement effect provides these critical properties to reinforced concrete (RC) structures. Textile reinforced cementitious composites (TRCC) have very good tensile, flexural and long-term performance. The effect of confinement will occur in RC columns by using these multilayer composites as permanent formwork. In addition, thanks to the permanent formworks, the service life will be extended against the drawbacks of structural defects. In this study, TRCC circular permanent formworks were manufactured by using a newly developed PPR (Pull-Pour-Roll) technique and machine. A cementitious mortar was designed and 4 & 6 layers of PVA textile were selected for the production of composite permanent formworks. The most important feature of permanent formworks is that they are hollow, thin sectioned and three-dimensional structural elements. Four full-scale circular column specimens were tested in the laboratory under the combination of constant axial load and reversed cyclic lateral load. Two of the columns were constructed as permanent formwork, while others were reference specimens built by temporary formworks. Composite formwork columns and one of the reference specimens include insufficient lateral reinforcement whereas the other reference column has adequate lateral reinforcement. This study was conducted to evaluate the effects of TRCC permanent and conventional temporary formworks in RC columns on key parameters of confinement. These parameters are respectively the hysteretic response, strength, displacement ductility, stiffness degradation, energy absorption capacity, damping ratio, residual displacement, crack pattern and failure mechanism. Extensive experimental studies have shown that the lateral load capacities, ductility, initial stiffness and energy dissipation in composite formwork columns have increased considerably compared to conventional columns. Thus, the TRCC permanent formwork increases the efficiency of confinement. Consequently, there is a great potential for use of TRCC permanent formworks as an alternative for conventional formworks in the RC columns.