Inelastic stability of steel building frames | |
| Author | Chitti Vijakkhana |
| Call Number | AIT Diss. no.D9 |
| Subject(s) | Framing (Building) Building, Iron and steel |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering of the Asian Institute of Technology, Bangkok, Thailand |
| Publisher | Asian Institute of Technology |
| Abstract | Assuming elastic-perfectly plastic moment-curvature relation, a method for determining the ultimate load of steel frames is proposed. In terms of generalized stress resultant and generalized strain, i.e., moment stress resultant and curvature, strain reversal is taken into account, i.e., the unloading of plastic hinges is considered. The effect of the axial force on the moment capacity of a section is taken into consideration. The stiffness matrix is so derived that it is applicable to any piecewise elastic regime in the elastic-plastic deformation of a member, the effect of the axial force on the stiffness being taken into account by means of approximate stability function. Delta functions defining the formation as well as the unloading of plastic hinges are employed in the formulation. The numerical computation for the smallest critical load can be rapidly carried out by following the standard matrix procedure for calculating eigenvalues. Linear extrapolation schemes for predicting the load parameter at which a plastic hinge forms before and beyond the stability limit are used. The method of analysis facilitates the study of not only the stability limit, but also those states beyond and remote from this point. The failure of the frame is signified by either the loss of stability due to the formation of plastic hinges and secondary moments caused by axial force acting on the laterally displaced frame members, or by the formation of a beam mechanism. The formation of a sway mechanism coincides with the stability limit unless the latter occurs prior to the former. It is shown that, provided no unloading of plastic hinges occur, the value of the critical load parameter λc, hence the overall stiffness of the frame, is reduced at the formation of each plastic hinge. The overall stiffness of the frame can be effectively increased if the capacity of a member which causes a significant reduction in the value of λc is increased. This enables the designer to effect possible material savings through the revision of the capacity of frame members which are more effective in raising the ultimate load of the frame. The results of this study show that the proposed method of analysis can be conveniently applied to the practical design of unbraced steel building frames. A design procedure for multi-story frames is presented and demonstrated in details by means of simple numerical examples. A comparison of the result with that obtained by means of exact stability functions is made and found to be in good agreement. The influence of unloaded plastic hinges on the frame behavior is illustrated. The post-buckling behavior of the frame are traced up to the formation of a sway mechanism. |
| Year | 1973 |
| Type | Dissertation |
| School | AIT Publication (Year <=1978) |
| Department | Other Field of Studies (No Department) |
| Academic Program/FoS | Dissertation (D) (Year <=1978) |
| Chairperson(s) | Lee, S. L.;Nishino, F. |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 1973 |