Torsion considered with an increasingly great importance by structural engineers. Some of the typical cases are space frames, spandrel beams, beams supporting balconies, eccentrically loaded beams, spiral staircases, horizontally curved beams, skew bridges, etc. Transverse openings, in Reinforced Concrete (RC) beams may be essential required for accommodating utility services in a building structure. Provision of an opening through a beam, however, changes its simple mode of behavior to a more complex one. Therefore, the design of such beams needs special treatment.
Strengthening or retrofitting of concrete structures to compensate the presence of transverse opening not only depends on the applied material but also depends on the used technique. Carbon Fiber Reinforced Polymers (CFRP) plates, provide a more technical alternative to the traditional methods of strengthening in many cases as it gives high strength, low weight, corrosion resistance, easy and quick installation and less changes in structural geometry.
An experimental test program of twenty-one RC beams with central large openings subjected to pure torsion were strengthened by using additional layers of externally bonded steel or CFRP plates with different techniques. The behaviors of the tested specimens were investigated and compared to identify the effectiveness of each method and material of strengthening to increase the torsional strength of beam with different opening sizes.
The main conclusions and recommendations drawn from the study were discussed and summarized. The research shows that the methods of strengthening by using externally bonded steel strips fixed by eboxy and steel dowels and CFRP plates gave best results.