Torsional Behavior of CFRP Strengthening of SCC Box Beams with Web Openings under Repeated Loading

Abstract

Monotonic and repeated torsional loading frequently occur in many concrete structures. The loading and unloading action of repeated torsion places structures under greater damage and risk of failure than other types of loading. Therefore, keeping old infrastructure maintained, repaired, and upgraded has become an important priority and requirement. In this research, experimental work was done on pre-cracked self-compacted reinforced concrete box beams repaired (strengthened) with CFRP sheets to investigate the effect of web openings and CFRP sheets on the torsional behavior of tested specimens. Two groups of sixteen half-scale CFRP-strengthened RC box beams with different numbers of circular openings in the web, with a diameter of about 30% of the hollow box depth, were investigated. The first group (I), tested under monotonic torsional loading, comprised four unstrengthened RC beams and another four beams strengthened with CFRP strips, whereas the second group (II) consisted of the same details as the first one tested under repeated loading. The range of the repeated loading was about 30% and 60% of the ultimate load of the monotonic tests. The effect of opening and repairing (strengthening) with CFRP on the ultimate and cracking Torques, Torque-Twist Angle, steel strains, and modes of failure were displayed and discussed. Cracking and ultimate torques and the angle of twist of the tested beams were significantly reduced due to openings in the web, accompanied by increased values for the steel strains due to the presence of openings. However, the results showed that using CFRP strengthening techniques increased torsional strength, angle of twist, and decreased steel strain for all the tested beam specimens. Results revealed that repeated loading causes inelastic deformations in proportion to the number of loading cycles, more than static load deformations. Doi: 10.28991/CEJ-2023-09-12-06 Full Text: PDF