Numerical study on the revised rules for minimum degree of shear connection in propped and unpropped steel-concrete composite beams

in Proceedings of ICMS (2021, June 16)

The work presents a numerical study that focuses on steel-concrete composite beams using ductile headed stud shear connectors. The objective is to check the suitability of the proposed revised EN 1994-1-1 ... [more ▼]

The work presents a numerical study that focuses on steel-concrete composite beams using ductile headed stud shear connectors. The objective is to check the suitability of the proposed revised EN 1994-1-1 rules for the minimum degree of shear connection. Therefore, a non-linear 3D finite element model of simply supported composite beams was developed and validated against the analytical values of the plastic bending design resistance. The parametric study consists of 10 configurations where the relative slip at slab-beam interface was carefully investigated at different degrees of shear connection and propping conditions. Specifically, the slip at the minimum degree of shear connection shall not exceed the limit of 6 mm defined as the characteristic slip of ductile connector according to EN 1994-1-1. The results showed that the revised rules for unpropped beams delivers conservative results whereas one case with propped conditions exhibit a maximum slip significantly higher than 6 mm. [less ▲]

Load bearing mechanisms of headed stud shear connections in profiled steel sheeting transverse to the beam

Doctoral thesis (2021)

Composite steel-concrete floor solutions have become popular in the design of buildings thanks to the efficient combination of high tensile strength and ductility of steel with reinforced concrete ... [more ▼]

Composite steel-concrete floor solutions have become popular in the design of buildings thanks to the efficient combination of high tensile strength and ductility of steel with reinforced concrete elements in compression. To ensure the longitudinal shear transfer between the downstand steel beam and the concrete slab in composite beams, headed stud shear connections are generally employed with profiled steel sheeting transverse to the supporting beam. However, whilst the steel deck enhances the bending resistance of the slab, the performance of the shear connection decreases. Based on the evaluation of a large database of push-out tests carried out in the last 40 years, several design models have been proposed in the last decades to predict the resistance of studs but none of them provides safe and reliable results. This is related to the fact that the proposed design equations do not always consider appropriately the actual resistance mechanisms activated in the shear connection. Also, as the failure modes are typically observed at high displacements, no information on the resistance components at lower displacements is given. Therefore, a deep investigation on the sequence of the load bearing resistance mechanisms of headed stud shear connections was performed with the support of an experimental campaign of 21 full scale push-out tests and numerical simulations. From the analysis of the experimental results, it was seen that all the samples experienced rib punching at low displacements followed by concrete pull-out failure or stud rupture. The influence of several structural parameters was also assessed by comparing different test series. It was found that 200 mm wide recess and slab depth have a minor impact on the performance of the connection. Instead, the addition of waveform rebars increased the resistance by 26% as well as the slip capacity whereas the different position of the wire mesh did not show an important influence. To investigate specifically the behaviour of the shear connections, the distribution of the compressive stresses in the rib and the plastic hinges developed in the stud connector were evaluated by means of a validated finite element model. From the outcomes of the experimental and numerical study, three main load bearing phases were distinguished. At low displacements (Phase 1), the concrete is not damaged until the typical cone crack initiates at the edge of the rib and the stud deforms in bending. Subsequently (Phase 2), while the cracks propagate, the internal forces in the rib redistribute and the resistance is governed by the bearing stresses of the concrete in front of the connector. At large displacements (Phase 3), the front side of the concrete rib is highly damaged whereas the tension stresses in the stud increases significantly due to pulling forces. For further slips, this can lead to concrete pull-out or stud rupture as confirmed by the experimental studies. These insights were taken as a basis for the development of three respective mechanical models: cantilever model, modified strut and tie model (MSTM), and strut and tie model (STM). Whilst the first considers the system as a cantilever beam, the other two reproduce the concrete as a system of compression struts and the steel sheeting was modelled as tie elements. All the resistance functions were analytically derived in consideration of the experimental and numerical results in order to estimate the capacity of the shear connection at different displacements. As the STM focuses on the behaviour at large deformations, only the first two models were considered to predict the actual capacity of the shear connection. The design resistance of these two proposed models was finally calibrated according to the statistical procedure of EN 1990. [less ▲]

Different load bearing mechanisms in headed stud shear connectors for composite beams with profiled steel sheeting

in Steel Construction (2019), 12(3), 184-190

The current design rules of EN 1994-1-1 covering headed stud shear connectors for composite beams with profiled sheeting lead, in some cases, to an overestimation of the load bearing capacity. Owing to ... [more ▼]

The current design rules of EN 1994-1-1 covering headed stud shear connectors for composite beams with profiled sheeting lead, in some cases, to an overestimation of the load bearing capacity. Owing to their empirical nature, these equations are not able to capture the real behaviour of the connector. Therefore, the load bearing mechanisms of the shear connection are identified in this work with the support of experimental and numerical results. According to the static system proposed, the concrete rib is modelled as a system of diagonal struts in combination with the stud in bending. It was observed that at 1-4 mm slip, a 'strut and beam' mechanism prevails, where the resistance of the connector depends on the activation of the plastic hinges in the stud and on the capacity of the diagonal strut in front of it. By increasing the slip (approx. 4-10 mm), the surrounding concrete gradually crushes, while the tensile stresses at the edge of the rib reach the tensile strength of the material. Because of this loss of rotational stiffness, the bending moment in the stud decreases and the upper plastic hinge gradually moves towards the slab. At higher displacements (approx. 20-40 mm), high tensile forces develop in the stud due to non-linear geometric effects and the load is carried through a 'strut and tie' resistance mechanism, provided that the embedment of the stud is sufficient to prevent the rotation of the rib. As the slip increases further, failure occurs either in the form of concrete pull-out or stud rupture. [less ▲]

Numerical evaluation of the plastic hinges developed in headed stud shear connectors in composite beams with profiled steel sheeting

in Structures (2019), 21

For composite beams using novel steel sheeting, the current Eurocode 4 rules sometimes overestimate the load-bearing capacity of headed stud shear connectors. This is due to the larger rib heights and the ... [more ▼]

For composite beams using novel steel sheeting, the current Eurocode 4 rules sometimes overestimate the load-bearing capacity of headed stud shear connectors. This is due to the larger rib heights and the smaller rib widths in comparison with the old studies, which have been carried out to calibrate the current design equations. The RFCS Project “DISCCO” investigated this phenomena and the working group under mandate M515, CEN/TC250/SC4/SC4.T3 is enhancing this equation and working on a proposal to be taken over in the new version of Eurocode 4. The proposed new equation covers the failure behaviour of the shear connection more in detail. The test results show, that the failure consists in a combined concrete cone and stud in bending. Due to the geometry of novel steel sheeting, the load bearing capacity of the headed stud shear connector is no more limited by its shear capacity, but by its bending capacity. A 3D non-linear finite element model is developed and validated through the support of the DISCCO push-out tests. A good agreement between numerical and experimental results in terms of force-slip behaviour is achieved. Special attention of this work lies on the numerical evaluation of the number of plastic hinges n y : a stress-based procedure is presented and the results are compared to the equations presented for new Eurocode 4. The numerical simulations show that the upper plastic hinge moves up as the slip increases due to the progressive crushing of the concrete in the rib. From the parametric study, it turns out that n y is linearly proportional to the embedment depth. Compared to pre-punched hole decking, through-deck welding specimen activates less plastic hinges in the studs because of the higher stiffness provided at the base of the stud. [less ▲]

New mechanical model to predict the load bearing resistance of shear connectors with modern forms of profiled sheeting

Scientific Conference (2018)

The rules in EN1994-1-1 concerning the resistance of shear connections in composite beams with headed shear studs and steel sheeting relies on push-out tests, which have been performed between the late ... [more ▼]

The rules in EN1994-1-1 concerning the resistance of shear connections in composite beams with headed shear studs and steel sheeting relies on push-out tests, which have been performed between the late seventies and the early nineties of the last century. In the recent years, new geometries of metal decking have appeared on the market with the target to reduce the volume and weight of the concrete slab and to maximise the slab efficiency. The influence of these new geometries on the load bearing behaviour of shear connections has to be verified. Amongst others, the RFCS research project DISCCO investigated the shear stud resistance in combination with such novel steel decking. It turned out that, the current EN 1994-1-1 rules need to be modified especially for metal decking with narrow and deep deck ribs. Alternative analytical equations for the estimation of the shear resistance have been derived and statistically evaluated according to EN 1990. Details are presented in this contribution. [less ▲]