Analytical model for torsional response of RC beams strengthened with Ferrocement U-Wraps

Abstract

Wrapping technology is one of the most effective ways of strengthening concrete elements. Several research articles have confirmed the effectiveness of fibrereinforced polymers (FRP) as wrapping material for enhancing the strength of reinforced concrete (RC) elements. Wrapping three sides of RC members is a convenient method of strengthening the beams that support the slabs. Its cost effectiveness over FRP makes ferrocement a good substitute as a wrapping material for strengthening RC beams. Limited research is reported regarding the torsional strength of ferrocement U-wrapped RC beams subjected to pure torsional loads. In this paper, an analytical model to predict the torsional response of RC beams with ferrocement U-wraps is presented. This analytical model is based on Hsu’s softened membrane model. The analytical model is validated by conducting experimental tests. In this investigation, 12 RC beams wrapped with ferrocement on three sides are tested under pure torsional loading. The different categories of beams tested in this investigation are under-reinforced beams, partially over-reinforced beams (longitudinal and transverse) and completely over-reinforced beams. The variations of U wraps considered in this investigation are three, four and five layers of mesh reinforcement in the ferrocement. The test results indicate that the cracking torque does not depend on the number of mesh layers present in the ferrocement wrapping. Ferrocement wrapping is more effective in the post-cracking stage than in the pre-cracking stage. The increase in the number of mesh layers in the ferrocement increases the ultimate torsional strength of the wrapped beam irrespective of the categories mentioned. The proposed analytical model is capable of predicting the torsional response with reasonable accuracy.