Torsion strength enhancement of RC hollow beam web using steel diaphragms as in-plane technique

Sometimes the construction system complexity or beam's geometry imposes some difficulties in performing an external strengthening for RC hollow beam web. The main challenge is to select a proper strengthening method to overcome its low torsion strength to inplane and out-of-plane stresses. Accordingly, the main goal of this research is to judge the possibility to adopt or (suggest) a certain internal in-plane technique to enhance the torsion strength. Six hollow beam web specimens of dimensions (1600×200×200mm) are tested experimentally under torsion effect. The major adopted variables including, the presence or absence of in-plane diaphragms, number of in-plane diaphragms (one, three and five), and strengthen the in-plane steel diaphragm with CFRP sheet on one or both faces. The experimental results show the ultimate torque increased by about (36%, 73% and 100%) for the tested specimens strengthened by one, three and five in-plane diaphragms respectively. On the other hand, the ultimate torque capacity was increased by about (53-55%) for beam specimens which contain one steel diaphragm strengthened by one and two CFRP sheets at their faces respectively, in comparison with the non-strengthened beam. It can be concluded that the torsional capacity has been enhanced due to the contribution of the adopted method.