Moment Redistribution of Two-Span Fire-Damaged Reinforced Concrete T-Beams Strengthened with CFRP Sheets

Abstract

Experiments of seven two-span reinforced concrete (RC) T-beams were introduced. One T-beam was normal temperature control T-beam, and the other six T-beams were heated under ISO-834 standard fire. All T-beams had the same geometrical dimensions and reinforcement as well as the loading and support arrangement. The fire-damaged T-beams were classified into two groups according to the fire exposure time. Different fire exposure time including 60 minutes and 75 minutes were investigated. In each group, one T-beam was unstrengthened control T-beam, and the other two T-beams were strengthened with carbon fiber reinforced polymer (CFRP) sheets. The results showed the way of moment redistribution of T-beam changed greatly because of the influence of fire. Different from the normal temperature T-beam, the fire-damaged T-beams had obvious moment redistribution at the beginning of the loading because of the variable stiffness along the length of the T-beams. The stiffness equivalency method for evaluating the moment distribution of RC continuous beams after fire exposure is presented. The scope of application for proposed method is between concrete cracking and yield load. The proposed method is based on the principle of equivalent stiffness. Considering the reduced elastic modulus of concrete and steel bars for fire exposure, a procedure was developed for quantifying the amount of sagging moment and hogging moment that can occur in fire-damaged continuous beams with an external CFRP sheets strengthening or without. The proposed method was verified under the experimental results as well. The proposed stiffness equivalent approach is capable of predicting bending moment of fire-damaged RC continuous T-beams with an accuracy that is sufficient for design purposes.