Seismic Behavior and Design of Connections for CFT Column Systems

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9520279 Ricles One efficient means of composite construction is the concrete filled steel tube (CFT) column- wide flange steel beam system. The filling of the tube increases the stiffness and strength of the system. This form of construction also produces a very cost effective structural system by combining the attributes of structural steel (speed of construction, strength, long-span capability, lightweight) and concrete (stiffness, damping, economy), where the tube provides a convenient formwork for placing the concrete. One of the key elements in this type of construction is the structural connection between the beam and column. As part of a lateral seismic load resistant system the connection would be expected to be capable of transferring beam forces and moments to the columns. The behavior of connections is typically complex due to the inelastic, non- uniform, combined stress states that develop under loading. There presently is still a lack of knowledge related to the seismic performance and guidelines for seismic resistance design of CFT composite construction, particularly for connections. This study will focus on the seismic behavior of moment connections for CFT square column composite structural systems. The objectives are to: (1) study the force and moment transfer mechanism between the beams and a adjacent column, and the influence connection details have on this mechanism; (2) develop connection details that perform well under seismic conditions, and are cost effective; and (3) develop design guidelines for implementing the details in practice. The analytical investigation will consists of two parts. The first part will involve conducting nonlinear time history seismic analysis of open CFT column composite systems. The second part will entail conducting nonlinear finite element ana lysis of the connection in order to assess the affects various structural details have on the force and moment transfer mechanism and capacity of the connection. Affects of concrete crushing, steel tube local buckling, and panel zone deformation on connection performance will be assessed. The experimental program will involve the construction and testing of full scale beam column sub- assemblages for seismic loading conditions. These sub- assemblages will resemble the beam and column members and their connection in the interior joint region of the prototype theme structure. Each connection in a test specimen will consist of an innovative design, where the ductility demand and information on connection details obtained from the analytical study will be used to formulate these designs. The results from the experimental and analytical programs will then be used to formulate the design guidelines. This is a project supported under the year 1 program of the Civil Infrastructure Systems (CIS) solicitation NSF 94-154. ***