Steel fiber reinforced concrete wall-slab joints subjected to cyclic loading

Abstract

Study of steel fiber reinforced concrete (SFRC) as a construction material has increased significantly in recent years. This is attributed to the benefits that steel fibers provide to concrete, such as the increase of strength and deformation capacity. Since SFRC is an attractive alternative to conventionally reinforced walls when building low-rise earthquake-resistant houses, an experimental program of SFRC wall-slab joints was conducted. Quasi-static cyclic reversible loading was applied on two specimens reinforced with a steel fiber dosage of 30 kg/m3, with and without steel deformed bars. Additionally, one benchmark monolithic wall-slab joint, reinforced conventionally using deformed steel bars only, was tested for comparison purposes. A displacement-controlled loading protocol was applied until failure of the specimens was observed. The main objective of these tests was to better understand the load-deformation capacity of wall-slab joints reinforced with steel-fibers. The performance of the tested specimens was assessed in terms of evolution of cracking patterns, failure mode, hysteretic response and stiffness and strength degradation. Results showed that an adequate combination of steel fibers and deformed steel reinforcement can lead to a satisfactory behavior of wall-slab joints, equivalent to those reinforced solely with deformed steel bars; while using only steel fibers can lead to smaller resistance and deformation capacity (about 60% that of the benchmark specimen). For the three tested specimens, the failure mechanism was dominated by flexural deformation at the slabs, close to the wall heel, where damage tended to be concentrated. A significant pinching behavior was seen in the hysteretic curves of the specimens. Stiffness degradation of the wall-slab joints was similar for the three specimens and it was directly related to the inter-story drifts demanded on them. Significant reductions were seen, with values as low as 20 and 10% of the initial stiffness, for inter-storey drifts of 0.002 and 0.01, respectively. Strength degradation was significant when only fibers where used, and small when they were combined with deformed bars.