Research on strengthening and toughening mechanism of special-shaped steel fiber concrete

To understand the strengthening and toughening mechanism of special-shaped steel fiber concrete, a numerical simulation was conducted considering the morphology of steel fiber. Based on the plastic damage mechanics theory and the constitutive relationship of the interface bonding between steel fiber and concrete, a model of a single special-shaped steel fiber pulling out from concrete was established by using the finite element method. After that, the pullout force-slip curve, the local stress variation of the single fiber, and the nephogram of concrete damage evolution were obtained. There are two peaks in the pullout force-displacement curves of the end hooked steel fiber, one peak caused by the shape changing of the fiber, and another caused by the interface debonding between the fiber and the concrete. Compared with the straight fiber, the pullout force gain ratios of type I and type II fiber are 14.5% and 24.41%, respectively. However, the maximum mean stress in type I steel fiber is around 10% larger than in type II steel fiber. It is found that the concrete corresponding to the type II steel fiber is damaged more severely than concrete corresponding to the type I steel fiber, the maximum compression damage degree is approximately 10% greater. For getting a better strengthen and toughen performance of the fiber concrete, the matching of fiber and concrete is essential to maximize the effectiveness of both fiber and concrete. The method proposed in this paper provides a theoretical reference for optimal steel fiber reinforced concrete design.