Inelastic Static and Dynamic Response of Frame Tube Structures

Abstract

<p>A study has been made for the ineslastic response of a thirty story frame tube structure subjected to static loading as well as dynamic excitation. The intent of this study was (i) to develop a simplified model for frame tube structures in order to compute both elactic and inelastic responses of such structures when subjected to lateral loadings, (ii) to identify the parameters that govern the behavior of frame tube structures, (iii) to assess the significance of the tube action on the elastic as well as inelastic responses, and (iv) to provide guidelines to estimate the structural responses when subjected to multiple components of earthquake ground motions.</p> <p>The simplified model reduces the 3-D frame tube system into sets of plane frame, interconnected by 3-D beam column elements. It is shown that this model gives good accuracy for each of the static and dynamic loading cases when compared with the results based on a 3-D model. The computer time involved with the planar model is at least one third that for the 3-D model. Therefore, it is beleived that the proposed model is a viable tool for the inelastic analysis of frame tube structures.</p> <p>The tube action if referred to as the forces developed in the two frames that are orthogonal to the direction of loading and which provide partial resistance to the applied loading. In order for this tube action to be effective, it is found that the frame tube should deflect like a cantilever with linear variation of axial force in the columns of the longitudinal frames and almost uniform axial force in the columns of the transversal frames. The key parameter that governs the inelastic dynamic response of frame tube structure was found to be the change of the post elastic story stiffness from the elastic story stiffness. For a large change of story stiffness, the bottom stories suffered large interstory drift. However, by decreasing such changes, the interstory drift became more evenly distributed along the height of the structure.</p> <p>The inelastic response when the frame tube is subjected to a bidirectional excitation is finally presented. It is found that the approximate estimates suggested by design codes underestimate the response. An alternative was proposed to give a more realistic estimate. Such scheme is the simple summation rule.</p>