Experimental and numerical investigations of steel fiber reinforced concrete dapped-end purlins

Dapped-end beams (DEBs), also known as thinned end beams, are often experienced in shear damages under the effect of vertical loads. Especially if the necessary precautions for thinned ends of reinforced concrete prefabricated purlins on the roofs having standard cross sections are not considered during the design, these purlins can be failed suddenly under the accumulated snow loads. This situation causes the roof to collapse completely. In order to mitigate this drawback, it is aimed to improve shear capacity of the purlins by using steel fiber reinforced concrete (SFRC) without changing the cross section geometry and reinforcement. Pursuant to this goal, experimental and numerical studies have been undertaken. The presence of steel fiber and the aspect ratio are selected as main parameters. The use of SFRC increased energy dissipation and shear capacities approximately 2.58 and 1.53 times, respectively. Moreover, the numerical analyses were performed in order to determine the optimum length of SFRC used in concrete from beam ends and fiber volume ratio to be used, and to investigate the effects of shear span to depth ratio (a/d). The results revealed that fiber volume ratio of 2% and the length of SFRC used up to the point where dapped-end region ends are recommended. Moreover, increasing the ratio of a/d results in a decrease in load carrying capacity.

Automated summary

Dapped-end beams are prone to shear damages under vertical loads, especially if precautions for thinned ends are not considered during design, leading to sudden failures under snow loads. The use of SFRC can significantly increase energy dissipation and shear capacities of beams without changing the geometry and reinforcement, with improvements of approximately 2.58 and 1.53 times, respectively.