Influence of transverse loading onto push-out tests with deep steel decking

This paper presents the results of 20 push-out tests on shear stud connectors, placed centrally in the ribs of 58 mm and 80 mm deep steel decking. The tests were designed to investigate the realistic load–slip behaviour of the shear connectors and the influence of transverse loading. The tests considered two different stud diameters and the effect of concentric and eccentric transverse loading. In addition, the influence of a second layer of reinforcement, thewelding procedure and the number of shear connectors in each rib have been considered. The observed influence of these parameters on the load–slip behaviour is presented and explained with regard to material properties and load-bearing models. In addition, the test results are compared with the current analytical approaches,which are shown to be non-conservative in some cases, because the presented deck shapeswere not well considered in the development and calibration of EN 1994-1-1

Serviceability performance of steel-concrete composite beams

YesFor composite beams with low degrees of shear connection, additional deflections occur due to slip in the shear connectors, which can be significant for beams with low degrees of shear connection. A design formula is presented for the effective stiffness of composite beams taking account of the stiffness of the shear connectors, which is compared to measured deflections of 6 symmetric beams and an 11m span composite beam of asymmetric profile. It is shown that the comparison is good when using a shear connector stiffness of 70 kN/mm for single shear connectors and 100 kN/mm for pairs of shear connectors per deck rib. Results of push tests on a range of deck profiles confirm these initial elastic stiffnesses. To ensure that the slip at the serviceability limit state does not lead to permanent deformations of the beam, it is proposed that the minimum degree of shear connection should not fall below 30% for un-propped beams and 40% for propped beams of symmetric cross-section.European Commissio

On the behaviour of shear stud connections in composite beams with deep decking

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

Push-out tests with modern deck sheeting and realistic transverse loading

The push-out test as proposed in EN 1994-1-1 originally was developed for solid slabs and not for composite slabs with additional steel sheeting. It leads to a load-slip behaviour of headed shear stud connectors which differs from the behaviour in the real beam. In particular, the vertical forces and negative bending moments of the composite slab at its support are ignored by this setup. Within the European research project “Development of improved shear connection rules in composite beams (DISCCO)” a total of 70 push-out tests was performed to investigate a more realistic push-out test setup. The influence of the transverse loading was investigated to develop a standard push-out test when additional steel sheeting is used. The test regime used to apply transverse loads in this investigation is described and the results of 10 push-out tests with 80 mm deep steel sheeting with pairs of 19 mm diameter headed shear stud connectors are presented. The observed bearing capacities of the shear connectors were over-predicted by the empirical reduction factor given in EN 1994-1-1 and the 6 mm criterion was not always satisfied, especially when no or only low transverse loads were applied. The application of transverse loads improved the ductility of headed shear stud connectors and the bearing capacity increased by up to 41%

Push out test of novel deep steel decking-failure modes and influence of transversal loading

This paper presents the results of push-out test specimens on shear connectors for composite beams, which are placed centrally in the ribs of novel formed deep steel decking. These deck shapes have not been well considered in the development and the calibration studies of EN 1994-1-1. The presented tests have been designed to investigate the additional failure modes and the corresponding load-slip behaviour, with special consideration of the newly occurring failure modes in the rib. In addition, the vertical loading of the slab has been considered in the push-out tests by a transverse load, acting with the help of a supplementary hydraulic jack. The differences between a concentric and eccentric transverse loading and a constant and variable transverse loading was investigated in the test series

Short-span composite beam tests to evaluate stud resistances

The results of a parametric study on ten short-span composite beam tests with small degrees of shear connection between 12 and 46% are presented. The beam tests were conducted using composite slabs with two modern forms of profiled steel sheeting. Important parameters of the shear connection, such as stud diameter, number of studs per rib, reinforcement pattern, welding procedure and concrete strength, were varied. All the test configurations were selected in accordance with a previously conducted study on the behaviour of shear connectors in push-out specimens. A comparison of the bending resistance of the beam tests and the calculated plastic bending resistance is presented. The shear connector resistances were taken either from the push-out test results or from the analytical methods of Konrad, EN 1994-1-1 and Nellinger. Evaluation of the push-out and beam test results showed that the current shear connector resistances in EN 1994-1-1 insufficiently predict the observed concrete failure modes and resistances in the presence of modern forms of steel decking. New approaches to the shear connector resistance proposed by Konrad and Nellinger led to more accurate predictions of the shear resistance of headed studs and the plastic bending resistance of the composite beam tests