Torsional Strengthening of Precast Wet Connections Using Stainless Steel Wire Mesh (SSWM)- Experimental study

Abstract

Generally concrete structure experiences different varieties of internal and external stress and strain when it is subjected to external loading. Apart from all main key actions are axial force, shear force, bending moment, and torsion. Beam is one of the basic Reinforced Concrete (RC) structural elements which is subjected to bending moments and shear forces under effect of external loads. For design of such a section subjected to bending moment and shear force, various design guidelines are available. But very less attention is given when members are subjected to torsion. In many cases, such as helical stair, beam supporting cantilever slab, curved bridge deck subjected to eccentric load, electric pole subjected to loads from wires on one side, spandrel beam, inverted T-beam supporting precast slabs etc. are subjected to significant torsional loading. The structural element subjected to torsion show cracking if they are not designed and detailed properly. Further change in loading or deterioration of structural element cause the deficiency in torsional resistance. Again, specially for Precast structure which is subjected to pure torsion for wet connections is not explored yet. To strengthen such Pre cast structural element with wet connections in torsion, different strategies and different FRP materials for retrofitting can be used. Research in area of strengthening of Precast RC structural members with wet connections using Stainless Steel Wire Mesh (SSWM) subjected to pure torsion is not researched yet. The major objective of the present major project is to study improvement in torsional resistance of Precast wet connection beams with different configuration of SSWM wrapping. An experimental study is conducted on the precast wet connection beams which is strengthened using SSWM with different configurations. A total of 26 beams with M25 grade of concrete are prepared. The cross-sectional dimensions of the specimens are 150 mm × 150 mm with 4-10 mm diameter longitudinal bars and 2 legged 8 mm diameter stirrups at 150 mm c/c. The length of the specimens is 1.3m. Total 2 beams are designated as control specimens and 24 beams are Precast beams with wet connection. out of 24 beams each 8 beams specimens are categorised with plain precast wet connections, outward shear key type wet connections & inward shear key type wet connections. In this wet connection, after casting of 2 small beam with 575mm length welding is applied on the central 150mm reinforcement overlapped portions. This 150mm gap is filled with Micro concrete. This Precast beam will be strengthened using SSWM wrapping with 3 different wrapping configurations. SSWM wrapping configurations considered for beams under pure torsion are 100 mm central Strip Wrapping (SW), COrner and 45o Degree Diagonal strip Wrapping (CO&DW) and Full Wrapping (FW). To investigate effectiveness of strengthening material and to work out better alternative for torsional strengthening, an experimental study is conducted. Angle of twist at interval of torque, Torsion at first crack, Angle of twist at first crack, Ultimate torque and Ultimate twist are measured and comparison is made between Unstrengthen RC beam & Precast beam with strengthened precast beam. Also, the failure patterns of specimen are reported.