Elastoplastic Nonlinear Analysis of Flexibly Jointed Space Frames

Abstract

Conventional approaches to the design and analysis of steel frames commonly assume the structure to be of either simple or rigid construction. In the simple construction approach, connections between members are not capable of transmitting moment, whereas in the rigid construction approach, full rotational continuity is provided. In practice, however, most connections are semirigid—possessing some degree of rotational stiffness as a function of the applied load. A method for the nonlinear analysis of space frames incorporating the effect of flexible or semirigid joints is presented. A two‐node zero length connection element with three rotational degrees of freedom per node is used to model the joint. The connection element may be introduced at one or both ends of a general thin‐walled beam‐column element, via kinematic transformation and static condensation. The proposed connection element may be represented by any set of nonlinear coupled or uncoupled, in‐plane, out‐of‐plane, and torsional moment‐rotation relationships. Several numerical examples are presented, which show that the response of a flexibly jointed frame is very sensitive to joint behavior.