Torsional Strengthening of RC Element using Stainless Steel Wire Mesh (SSWM)-Numerical and Analytical Study

Abstract

Generally Reinforced Concrete (RC) structural elements are designed for axial force, shear force, bending moment and torsion moment. Due to this type of loading concrete structures experience complex stresses and strains. Sometimes torsional moment in structural element may be so large that it can increase the principle diagonal tensile stress and this tensile stress can develop cracks which cause catastrophic character of the torsional failure of members. Strengthening of structural elements are necessary in case of increase in loading, deterioration/damage of structure, modification in structural systems, error in construction etc. Stainless Steel Wire Mesh (SSWM) is locally available strengthening material. SSWM is a cost effective strengthening material compare to other available strengthening materials in market. Research in area of strengthening of RC elements using SSWM is not attempted in greater details. Most of the experimental studies on torsional strengthening of RC element using SSWM have been published recently. In order to gain a better understanding of the torsional behaviour of SSWM strengthened RC beam, the main objective of the study is to evaluate numerically and analytically response of SSWM strengthened RC element with difference wrapping schemes. The numerical simulation is performed using finite element (FE) based software ABAQUS. The three dimensional nonlinear FE analysis based on concrete damaged plasticity (CDP) model is used for numerical simulation of SSWM strengthened RC element under pure torsional loading. The type of specimen on which FE analysis carried out are RC precast beam, RC square beam, RC hollow beam and RC T-beam. SSWM wrapping configurations considered for RC square beams are 300 mm strip wrapping (CE300S), corner and 100 mm strip wrapping above stirrups (CO&100SAS), corner and 100 mm strip wrapping in between stirrups (CO&100SIS), diagonal strip wrapping at 45° (D45W), corner and diagonal strip wrapping (CO&DS) and full wrapping (FW). SSWM wrapping configurations considered for RC hollow beams are corner and 100 mm strip wrapping above stirrups (HCO&100SAS), corner and 100 mm strip wrapping in between stirrups (HCO&100SIS), corner and diagonal strip wrapping (HCO&DS) and full wrapping (FW). SSWM wrapping configurations considered for RC T-beams are 100 mm strip wrapping above stirrups (T&100SAS), corner and 100 mm strip wrapping above stirrups (TCO&100SAS), 100 mm strip wrapping in-between stirrups (T&100SIS), corner and 100 mm strip wrapping in-between stirrups (TCO&100SIS) and U-shape wrapping on beam (TUW). Three different wet connections considered for RC precast beam are without shear key type, outward shear key type and inward shear key type wet connections. Different wrapping configuration of SSWM is employed on central 400 mm region over wet connections. SSWM wrapping configuration considered for all three precast wet connections are 100 mm strip wrapping (SW), corner and diagonal strip at 45° (CODW) and full wrapping (FW). In RC precast connections torque-twist behaviour is compared with experimental results. A close match between experimental results and FE analysis is observed. It is found that inverted shear key (ISK) type wet connections gave better results compare to other wet connections. Comparison of different strengthening configuration is made to find out effectiveness of wrapping on precast connections. It is also found that strip wrapping (SW) type wrapping configuration shows better ultimate twist compare to other wrapping patterns, it can be recommended for retrofitting of RC precast element under torsional loading. Comparison of torque-twist results and damage pattern of strengthened RC precast beam, RC square beam, RC hollow beam and RC T-beam is presented in this study. In RC square beam, specimen with corner and diagonal strip (CO&DS) of SSWM is exhibited better results compare to other specimens. In RC hollow square beam, full wrapping (FW) of SSWM is observed to be maximum increase in torque capacity. In RC T-beam, specimen with corner and 100 mm strip in between stirrups (TCO&100SIS) wrapping of SSWM higher value of results. Analytical study to predict full non-linear torsional analysis of RC element strengthened using SSWM is carried out based on softened membrane model for torsion (SMMT). Effect of torsion on RC element, constitutive relationship of materials and compatibility equations are studied and modified to consider strengthening effect of SSWM. An algorithm has been proposed to calculate torsional behaviour of RC element strengthened with SSWM. The model is capable to predict the pre and post nonlinear behaviour of torque-twist curve for full wrapped SSWM strengthened RC element.