Internal transverse strengthening of RC box beams subjected to torsional loads: A review study.

Sometimes in the practical cases, and due to beam's complexity or/and geometry of the construction system, it is difficult to perform an external traditional strengthening technique such as externally bonded of the steel elements, composites of fiber-reinforced polymer (FRPs), bonded of section enlargement....etc. As a result, the need for the alternatives simple techniques are arise. From the structural point view, the placing (inserting) an internal structural element such as steel bracing, steel diaphragms, RC diaphragms, internal framed steel stiffening ribs inside the longitudinal hollow of the RC box beams represents the best alternative methods instead of the traditional strengthening techniques. Strengthening of reinforced normal concrete (NC) or self-consolidated concrete (SCC) box beams by RC diaphragms, steel diaphragms or bracing, and FSSRs techniques are relatively new techniques and impactful issues to be addressed and seem to be limited and not covered in earlier studies. Despite the tested beam dimensions and adopted variables, the using of internal strengthening by RC diaphragms, steel bracing, steel diaphragms and framed-steel-stiffening-ribs (FSSRs) gives a significant improvement in torsion capacity by (43-94%), (14.4-82%), (36-100%) and (45.7-122.4%), respectively. The torsion capacity enhancement is associated with increasing of both transverse torsional stiffness and toughness as well as decreasing in deformation (torque-angle of twist relation). Also, it was observed that the arrangement and numbers of used internal strengthening elements have the main effect on the amount of enhancement. [ABSTRACT FROM AUTHOR]