Service load analysis of composite frames using cracked span length frame element

Abstract

A cracked span length frame element has been proposed for service load analysis of composite frames consisting of steel columns and steel-concrete composite beams. The element comprises a maximum of three regions (cracked or uncracked) with simplified formulation and is applicable for all types of loading. This element has been used in an analytical-numerical procedure for the inelastic analysis of such composite frames, subjected to service loads. Analytical expressions have been derived for flexibility and stiffness coefficients, end displacements, load vector and mid span deflections of the cracked span length frame element. Average values over the cracked regions have been used for the tension stiffening characteristics, so as to retain the analytical nature of the procedure at the element level. The procedure uses an iterative technique for establishing the cracked region lengths and the distribution coefficients (for tension stiffening), and yields the inelastic deflections and redistributed moments. The procedure using the proposed element has been validated by comparing the results with experimental results available in literature and also with the results obtained from finite element analysis. The procedure requires a fraction of the computational effort that is required for the numerical methods available in literature and gives sufficiently accurate results. Therefore, the reduction in the computational efforts in the case of high-rise composite frames would be considerable.