Abstract :
[en] Steel-concrete composite construction has many advantages for the construction of multistorey buildings. The use of composite beams acting compositely with the floor slab achieves longer spans and reduces the weight of the beams. The weight reduction can be further improved by replacing the solid concrete slab with a steel-concrete composite slab using steel decking.
However, using composite slabs reduces the shear forces that are transferred between the slab and the beam. This is because the number of studs in the span is limited by the deck geometry. In addition, the load-bearing behaviour of studs in the ribs of composite slabs is different to studs in solid slabs and shows typically a reduced resistance per stud.
Currently, [DIN EN 1994-1-1, 2010] applies an empirical reduction factor to the resistance of studs in solid slabs to analyse the resistance of studs in the ribs of composite slabs. A comparison to push-out test results shows that this formulae results in an unsatisfactory correlation. Furthermore, the reduction factor is unsafe in many cases with modern decking. The latest empirical reduction factors in [Konrad, 2011] are currently discussed as alternative to the rules of [DIN EN 1994-1-1, 2010]. They show a significantly improved correlation to test results and an increased field of application. A significantly higher correlation to test results is obtained with the mechanical model by [Lungershausen, 1988]. Because of the restrictive field of application and missing parameters, like the concrete strength, it is not discussed as replacement for the reduction factors.
A newly conducted series of push-out tests with modern deep steel decking shows the insufficiency of the presented analysis methods of the stud shear resistance, as the predictions were in general non-conservative. Furthermore, depending on the geometry of the shear connection, a new failure mode was observed: Rib pry-out failure. Investigation on concentric and eccentric transverse loading of push-out specimens, to consider the loading conditions of a real slab, show in general beneficial influences on the load-slip behaviour.
Based on the behaviour of the studs in push-out tests, equations for the shear connector resistance based on the failure modes are developed. A combined bending failure of the shear stud and the concrete rib is assumed. The observed failure modes in the tests are considered by different yield-lines of the shear stud. The shear resistance of the pure stud gives the upper bound for the shear connector resistance. The new equations show a good correlation to test results and are safe for modern types of steel decking. In comparison to [DIN EN 1994-1-1, 2010], the field of application is extended by the stud position, as in [Konrad, 2011], and deeper decking, as in [Lungershausen, 1988].
The analysis of the bending resistance of two accompanying beam tests confirms the accuracy of the new shear stud resistance. The beam tests have very low degrees of shear connection. The end-slip at ultimate load exceeds the limiting slip of 6mm, but at 95% of ultimate load the limiting slip is satisfied.
A numerical model for composite beams is verified against the test results. The model considers the shear studs as non-linear springs. A simplified load-displacement curve is presented and verified against real load-slip curves.
