STABILITY OF SPACE STEEL FRAMES WITH SEMIRIGID CONNECTIONS

The problem of stability of space steel frames with semirigid connections is investigated. The method used is based on the matrix approach, in which the global stiffness matrix of the structure is constructed by assembling the individual member stiffness matrices. The stiffness matrix for a member with general orientation in space is first derived. It includes the effect of the semirigidity of connections at the member ends, and the effect of the axial load on the bending stiffness of the member. The former effect is included by the introduction, at each end of the member, of rotational springs in the planes of bending, with stiffnesses dependent on the actual rigidities of the connections. The latter effect is accounted for through the use of stability functions. The critical buckling load for a member is determined as the value of the axial force in that member which renders the global stiffness matrix singular. A computer program is developed, with the capability of calculating the buckling length of any member of a space frame, for any frame geometry, and any specified values of connection rigidities. The program is used to study the stability of the members of a vertical bracing system of a complete space steel structure. The effect of the semirigidity of connections on the buckling behavior of such members is investigated. Three simple space models and one equivalent plane structural model are used and the results are compared with those obtained using the complete space model. The simplest structural model that achieves reduction in computing time, yet retains the accuracy of computation within the acceptable engineering tolerance, is identified for the future use of the program in obtaining the buckling length factors for members of vertical and horizontal bracing systems. These factors are required for the design of such members. © 1990.