Strengthening of RC dapped-end beams under torsional moment

Abstract

Maintaining and strengthening existing structures is a very important issue in terms of extending the service lifespan of structures. Reinforced concrete (RC) beams with dapped ends are frequently found in bridge girders and precast concrete constructions. The reduction in depth near the supports of RC beams tends to produce a stress concentration and hence requires special analysis and detailing of the reinforcement, especially in the case of torsional stresses. This paper introduces an experimental investigation for the torsional behaviour of recessed RC beams. Along with a control specimen, three beams strengthened using different techniques (the application of fibre-reinforced polymer (FRP) sheets, FRP laminates and external prestressed steel) were constructed and tested under torsion. The results of the research showed that the external prestressing technique produced a higher ductility than the other techniques. On the other hand, the use of external prestressing and carbon fibre-reinforced polymer (CFRP) wrapping to strengthen RC dapped beams subjected to torsional moment increased cracking and failure loads compared with the use of externally bonded CFRP laminate. A three-dimensional truss model is presented to calculate the forces in the stirrups and the ultimate loads for the external prestressing technique. The model shows good agreement with the experimental results.

Rollover instability of precast girders subjected to wind load

“…Few studies have been conducted on the lateral behaviour and instability of precast concrete girders using both experimental and analytical methods, because such studies are rather complicated due to the presence of various imperfect factors, such as the geometry, material and support conditions. These difficulties increase the need for a numerical method that can be used to evaluate the effects of various factors on the three-dimensional (3D) behaviour of structures, including the lateral stability of precast concrete girders (Atta and El-Shafiey, 2014;Guiglia et al, 2013;Heiza, 2013;Hou et al, 2016;Lee et al, 2015;Mullapudi and Ayoub, 2013;Najafian et al, 2013). In general, 3D solid and shell element models are used to evaluate the lateral behaviour and instability of bridge girders supported on an elastic bearing pad.…”