Experimental and analytical studies of the cyclic behavior of simple connections in steel frame buildings

In typical steel buildings, simple connections are used to transfer gravity loads and are assumed not to contribute to the lateral resistance of the structure. However, research has shown that these simple connections have some inherent strength and stiffness. Furthermore, research on composite connections suggested that the presence of the floor slab would cause a significant increase in bending moment capacity and rotational stiffness. Interest in the cyclic behavior of the simple connections, including the effects of the slab, was heightened by the events of the Northridge earthquake. Damage to steel structures in the Northridge event motivated an organized effort to evaluate various aspects of the state of practice in steel seismic design, including the role of the simple connections. The main objective of the research presented is to evaluate the contribution of the simple connections, including slab effects, to the lateral resistance of steel structures.; This objective is fulfilled through a combined experimental and analytical program. In the experimental program, sixteen full-scale specimens were tested under a combination of gravity loads and lateral displacements. The connection details were mainly chosen to represent current practice or existing structures. The specimens included typical shear tab connections, pre-80's shear tab details, stiffened seat, supplemental seat angle, and top-and-bottom angle connections with floor slabs. Some of the shear tab connections were tested without the floor slab, as well, to ascertain the role of the concrete floor. Some variations included the addition of steel reinforcement in the floor slab and the use of normal-weight concrete or lightweight concrete. Experimental results showed cyclic behavior that was typically governed by ductile mechanisms such as rotational slip, yielding, and elongation of bolt holes. The contribution of the floor slab effectively doubled the moment capacity of the tested shear tab connections, while crushing of the concrete at the column typically caused loss of the composite action of the slab by 0.04 radians of drift.; In the analytical program, measured cyclic response was used to develop moment-rotation models of typical shear tab and supplemental seat angle connections. Guidelines for evaluating the moment capacity, stiffness, and rotation capacity of typical connections were established. Parametric studies of steel moment frame buildings demonstrated when the role of the simple connections might be significant to the redundancy of the structure or calculations of drift. The resulting models and guidelines provide tools with which the structural designer can ascertain the contribution of the simple connections to the lateral resistance of a steel structure.