Behaviour of Stainless Steel Wire Mesh Strengthened Reinforced Concrete Column under Axial Force and Torsion

Abstract

Reinforced Concrete (RC) columns are subjected to external loading such as axial force, bending moment, torsion and combinations of both axial force and bending moment or torsional moment. These loads/load combinations may arise, because of the irregular structural configuration and as well as when a bridge is subjected to a horizontal transverse earthquake action. All these factors instigate distress in structural elements, and overtime the load carrying capacity of the elements deteriorates with age, leaving the complete structure vulnerable to collapse. So to enhance the load carrying capacity and life span of distressed structure, repair and retrofitting is must. For repair works different types of materials are available: Carbon Fiber Reinforced Polymer (CFRP) and Glass Fiber Reinforced Polymer (GFRP). To overcome hurdle of high cost and the possibility of debonding from concrete surface, Stainless Steel Wire Mesh (SSWM) can be an effective alternative to CFRP and GFRP. Research in area of strengthening of RC column using SSWM subjected to combine axial and torsional load is not attempted in greater extent. The main objective of the present study is to develop assembly to apply axial and torsional load and to study the improvement in combined axial and torsional resistance of RC columns with different configuration of SSWM. Partial SSWM wrapping on to concrete columns required less SSWM materials and can be applied easier and faster than the full wrapping. To understand the effectiveness of partially wrapping of SSWM on concrete cylinder under compression load total 18 concrete cylinder is casted. An experimental program was first carried out to investigate the performance of particular SSWM confined concrete with varying strip gaps. The axial load-axial deformation behaviour, axial stress-axial strain behaviour of both wrapped and non wrapped cylinders are investigated. The performance of partially wrapped SSWM on concrete significantly reduce with increase of strip gap. When the strip gap exceeds the diameter of the specimen, the confinement effectiveness become negligible. Based on experimental results of cylinders, total 7 RC square column specimens with M25 grade of concrete are prepared. The cross sectional dimensions of column specimens are 150 mm x 150 mm and 1300 mm in length with 4-10 mm diameter longitudinal bars and 2 leg 8 mm diameter stirrups at 150 mm c/c. Total two column are designated as control specimens and five columns are strengthened using SSWM wrapping with five different configuration. While wrapping the RC column result of partially wrapped cylinder are taken in to account. SSWM Wrapping configurations considered for column under axial force and torsional load are CEntral 300 mm Strip Wrapping (CE300S), COrner and Strip wrapping In between Ties (CO\&100SIT), COrner and Strip wrapping Above Ties (CO\&100SAT), COrner and Diagonal Strip wrapping (CO\&DS) and Full Wrapping (FW). These specimens are tested for combined axial force and torsional load in newly developed loading frame. The torsional moment and twist at first crack and at an ultimate stages as well as torque-twist behavior of SSWM strengthened specimens are compared with controlled specimens. Failure pattern and strain at different location on columns are observed. The specimen with COrner and Strip wrapping Above Ties (CO\&100SAT) exhibited 105.5 % increase in cracking torque and 76.5 % increase in ultimate torque compared to control column but specimen exihibited less angle of twist compare to specimen COrner and Strip wrapping In between Ties (CO\&100SIT).