EFFECT OF TENSILE STRENGTH CONSIDERING SIZE EFFECT AND LOADING RATE ON OPTIMUM DESIGN OF ARCH DAM

Unreinforced mass concrete tensile strength is the most important parameter in concrete dams design. Actually, concrete strength is affected by several factors such as section size, type and rate of loading, and material and mixture properties. As is well known, concrete member tensile strength tends to decrease when its size increases. Obviously, in concrete dams with large sections, this effect is more pronounced. In this study, we aimed to investigate the major changes in the shape and volume of optimal arch dams designed taking into account the factors mentioned above, especially the structural section size effect on concrete resistance. To this end, the apparent tensile strength proposed by Dungar on the basis of Bazant size effect law was used. The results obtained were compared with the designs based on classic or Raphael tensile resistance criterion. To design the dams, CADSO, the software for optimization of arch dam shape, was used, and its design improved in order to apply the aforementioned resistance equations. The new software is able to determine the optimized shape of dam by meeting various constraints, such as tension limitations, resulting from loading combination conditions including body weight, water pressure, and seismic status while considering sections size and type and rate of loading. The results of studies on the great Shahid Rajaee Dam suggest that the optimized design based on the principles of fracture mechanics increases the thickness of sections, especially in the tensile stress concentration positions near the foundation. The process changes the optimal shape pattern of the dam body shell increasing its volume, for the case studied. According to the results mentioned, it appears that there is a serious concern with the conventional design of concrete dams; size effect has to be taken into account for the safe design of concrete dams shape.