Modeling modular steel structures has to account for their unique details. The vertical connection between modular units typically involves partial welding of the columns of a lower and an upper modules, which may lead to independent upper and lower rotations at the same joint.
A proposed analytical model of the vertical connection between columns of a lower unit and the top floor beam of an upper unit is shown below. Rigid end blocks (shown by thick dark lines J1-J2, J3-J4, J5-J4, and J6-J4) were provided at each end of frame members to capture the rigidity of connection regions. The short column segment between the bottom flange of the floor beam and top flange of the ceiling beam was represented by a vertical beam-column element, M1, whose height represents the clearance between the two beams. This vertical element was pinned internally into a common joint with the bottom flange of the floor beam, J2, such that an independent upper and lower module rotation would develop at this joint. Joints J3 to J6 are modeled as continuous.
For more information, please refer to:
Annan C.D., Youssef M.A., El-Naggar M.H., 2009, “Experimental Evaluation of the Seismic Performance of Modular Steel Braced Frames”, Engineering Structures, 31(7): 1435-1446.
Several studies have shown that the lateral response of concentrically braced frames is dominated by the inelastic behavior of the bracing members. However, the overall performance of the entire frame depends on the frame configuration including its connections. In this study, the hysteretic characteristics of modular steel braced frames under reversed cyclic loading are evaluated. The design and construction of the test specimen accounted for the unique detailing requirements of these frames. A regular concentrically braced frame with similar physical characteristics was also tested for comparison. Both test specimens consisted of a one-storey X-braced system with tubular brace cross-section. This paper describes the behavior characteristics and provides a detailed comparison of the two systems to assess the strength, stiffness, inelastic force and deformation, and energy dissipation characteristics of the modular system. An analytical model capable of capturing the effect of the system’s unique detailing requirements is proposed and validated using the test results.
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