Retrofitting of Beam Subjected to Pure Torsion using Stainless Steel Wire Mesh (SSWM) and Ferrocement

Abstract

Change in loading or deterioration of Reinforced Concrete (RC) structural element cause the deficiency in torsional resistance. To strengthen such structural element in torsion, different strategies of retrofitting can be used. Research in area of strengthening of RC members using Stainless Steel Wire Mesh (SSWM) and ferrocement subjected to pure torsion is not attempted in greater detail. The major objective of the present major project is to study improvement in torsional resistance of Reinforced concrete (RC) beams with different configuration of SSWM and ferrocement wrapping. An experimental investigation is conducted on the RC beams strengthened using SSWM as well as ferrocement wrapping. A total of 16 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 leg 8 mm diameter stirrups at 150 mm c/c. The length of the specimens is 1.3 m. Total 2 beams are designated as control specimens and 12 beams are strengthened using SSWM wrapping with 6 different wrapping configuration. Remaining 2 beams are strengthened using ferrocement wrapping. SSWM wrapping configurations considered for beams under pure torsion are 300 mm central strip wrapping(CE300S), corner and strip wrapping at the location of stirrups(CO&100SAS), corner and strip wrapping in between stirrups(CO&100SIS), diagonal strip at 45° wrapping(D45W), corner and diagonal strip wrapping(CO&DS) and full wrapping(FW). Side wrapping (FS) and U-shaped wrapping (FU) are considered for strengthening using ferrocement. To investigate effectiveness of strengthening material and to work out better alternative for torsional strengthening, an experimental study is conducted. For validation, numerical investigation is also carried out using finite element (FE) based ABAQUS software. 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 strengthened RC beam and control beam. Also the failure patterns of specimen are reported. Based on the investigations presented in this project report, it is observed that reinforced concrete beams wrapped with different configuration by SSWM wrapping and by ferrocement wrapping exhibited significant increase in their cracking and ultimate strength as well as ultimate twist deformations compared to control specimens. Corner and diagonal strip wrapping (CO&DS) is most efficient in enhancement of the torsional resistance of reinforced concrete beams compared to other SSWM configurations when beams are tested in pure torsion. RC beam with full SSWM wrapping resists higher torque as compared to D45W specimen but experiences small angle of twist as the full SSWM strip is active in resisting torsion. Nonlinear finite element analysis of reinforced concrete beams and RC beams strengthened using SSWM and ferrocement is carried out to simulate torque vs. twist behavior. Results of FE analysis of beams under pure torsion shows reasonable agreement with experimental results. From comparisons of the FEM results with experimental data maximum difference of 39% and 17% is observed in ultimate torque and ultimate twist, respectively. Pre cracking behavior under pure torsion simulated by FEM has good agreement with experimental data. Results of SSWM strengthened RC beam are compared with available data of torsional strengthening by Glass Fiber Reinforced Polymers (GFRP) and Carbon Fiber Reinforced Polymers (CFRP). FW and CO&DS specimen, strengthened by SSWM shows 53% and 44% higher values of cracking torque respectively when compared to GFRP strengthened beams. In contrast, at ultimate torque for specimen CO&100SIS and CO&DS, beam specimens strengthened using GFRP are showing nearly 36% and 23% higher value respectively when compared with similar SSWM strengthened beams. SSWM is easily available in market and is low cost material as compared to GFRP and CFRP material. Stainless Steel Wire Mesh (SSWM) can be economical alternative of strengthening of RC beams subjected to torsion.