The main objective of this research was to evaluate the potential of using steel fiber reinforced concrete in slab-column connections for increasing their punching shear strength and deformation capacity when subjected to earthquake induced lateral displacements. The research was divided in three phases. In the following, a brief description of the scope of each phase and its objectives is provided.
In the first stage, a series of slabs with different types of fiber reinforced concretes was tested under monotonically increased concentrated load. A total of five pairs of slabs, four pairs constructed with fiber reinforced concrete and one pair with regular concrete were tested. Two flexural reinforcement ratios were evaluated for each material. The main objectives of this research stage were: 1) to evaluate the potential of various fiber reinforced cement-based materials for increasing punching shear strength and deformation capacity of slab-column connections subjected to monotonically increased concentrated load; 2) to evaluate the influence of flexural reinforcement ratio and rotation on punching shear strength; and 3) to select the best materials for further study under earthquake-type loading.
In the second research stage, the behavior of two approximately 1/2-scale slab-column connections constructed with the fiber reinforced concretes that showed the most promise, based on the results from the Stage 1 tests, was evaluated when subjected to combined gravity load and uni-axial lateral displacement reversals. The objectives of this research phase were: 1) to study the effect of gravity-induced shear on the rotation (and drift) capacity of fiber reinforced concrete slab-column connections subjected to uni-axial displacement reversals; and 2) to evaluate the effect of fiber geometry and strength on the deformation capacity of connections subjected to combined gravity load and lateral displacement reversals.
The final research stage was aimed at evaluating the behavior of fiber reinforced concrete connections under bi-axial lateral displacements, as well as that of a nominally identical connection reinforced with shear studs, which was intended to represent current design practice. For this purpose, three nearly full-scale slab-column subassemblies were tested under combined gravity load and bi-axial lateral displacement reversals. The objectives of this research stage were: 1) to evaluate the effect of bi-axial lateral displacements on the rotation capacity of fiber reinforced concrete slab-column connections; 2) to compare the seismic performance of the proposed fiber reinforced concrete connection design with that of a typical connection design with shear stud reinforcement; and 3) to evaluate the ability of shear stud reinforcement to resist punching shear stresses in connections subjected to combined gravity-induced shear and bi-axial rotations.
Experimental work associated with Stages 1 and 2 was conducted at the University of Michigan Structural Engineering Laboratory, while testing associated with Stage 3 was conducted at the University of Minnesota NEES-MAST (Network for Earthquake Engineering Simulation - Multi-Axial Subassemblage Testing) Facility.
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