Influence of seat angles on the behaviour of cold-formed steel concrete composite joints

Abstract

This paper presents an experimental study on cold-formed steel (CFS) concrete composite joints, with and without seat angles, to investigate their structural behaviour and determine the influence of seat angle on this kind of connection. These CFS-concrete composite joints were made up of a cold-formed steel (CFS) connection consisting of two lipped CFS C-channels (bolted back-to-back as a beam and column with a trough plate or gusset plate), a composite slab (comprising a reinforced concrete slab with profiled CFS deck, and bolted shear connectors). In the literature review, the CFS-concrete composite beams and composite slabs were found to have been investigated experimentally and analytically in several studies but little attention has been paid to CFS-concrete composite joints. This is the reason for the current investigation on these kinds of composite joints. Six full-scale specimens of composite joints, three bare joints and three seat-angle joints, were evaluated experimentally by isolated joint tests, in which a one-point load was monotonically applied to the beams. The responses of the specimens were recorded by measuring instruments: i.e. five LVDTs, two inclinometers, and five strain gauges. The results obtained were used to provide moment-rotation relationships of the connections, which were necessary for quantifying the key characteristics of the connections. The three linear moment-rotation responses of the tested composite joints showed that adding the seat angles to the CFS-concrete composite joints increases both their moment resistance and rotational stiffness (by 8% and 21%, respectively), and reduces the rotation capacity (by 17%), on average. Furthermore, it was observed that the behaviour of these types of joints tends to transform from partial strength to full strength by adding a seat angle.