Semi-rigid composite action: Experimental analysis and a suitable model

Abstract The partial continuity provided by semi-rigid joints in composite structures was indicated by previous studies as an important factor affecting the frame performance. However, the limited knowledge of the behavioural mechanisms of such joints hampers their practical use. A research project aimed at developing criteria and methods suitable for the design analysis of a composite semi-continuous framework is in progress at the universities of Trento and Trieste. This paper illustrates the main results of the second series of tests, which were conducted to find the influence of the shear connectors' flexibility, of the interaction between the concrete slab and the column, and of the imbalance in the moments at the two joints of an internal node. The problem of determining the joint rotation when the experimental measures relate to a beam cross-section distant from the column face is then discussed. Finally, to describe the response of the node a spring model is proposed, which is able to recognize the degree of rotational interaction between the joints and the column, depending on the structural detailing. A joint-column continuity factor is defined and its possible use in design analysis is indicated.