Nonlinear formulation for tubular X-joints in frame analysis

Abstract

This paper presents a set of new joint formulations to describe the load-deformation characteristics for Circular Hollow Section (CHS) X-joints under monotonic brace axial compression. The proposed formulation couples the ultimate joint strength with the nonlinear deformation to determine the resistance of the joint at varying levels of the applied displacement. The ultimate joint capacity used in the current formulation follows the mean strength equations in the latest IIW recommendations, while the geometric-dependent parameters derive from regression analyses of a calibrated finite element investigation covering a practical range of joint parameters. This proposed formulation for CHS X-joints also includes the redevelopment of the joint strength at the contact of two opposing brace members under compression. The experimental results from the large-scale 2-D and 3-D frame tests validate the accuracy of the proposed formulation, which is implemented in a nonlinear pushover analysis as user-defined joint-spring elements. © 2012 Taylor & Francis Group, London.