Experimental investigation and simulation on load-transfer paths in optimally designed RC deep beams

Abstract

The main failure pattern for reinforced concrete deep beams is shear failure due to the low shear-span ratio. The Topology Optimization for the stress of rebar in this study is explored for aided-design of deep beams, which proves that the optimization can transform the brittle shear failure to ductile bending failure without reducing the bearing capacity of deep beams, compared with the traditional empirical method. In the process of increasing load, the displacement fields on the surface of the deep beams were measured successively by non-contact displacement gauges, and converted to the principal strain distribution. Then the distribution is used to fit correspondingly the principal stress trajectory and load-transfer paths of the specimens. The results show that, for the specimen designed with Topology Optimization, the built-in inclined main reinforcements are in line with the direction of the concrete tensile stress in the web of the specimens, and effectively restrict the development of width of the inclined cracks. Consequently, the integrity and directness of the load-transfer paths from the loading point to the supports are guaranteed. Meanwhile, the stress fields of the specimens correspond to the Michell-type structure, hence the stress of their rebar is almost under a full stress state. Therefore, the optimal design presents a more reasonable reinforcement layout, which can better control the accumulation of damage and the change of the load-transfer paths during the loading process, and finally achieve the desired failure pattern.