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

[EN] For composite beams using novel steel sheeting, the current Eurocode 4 rules sometimes overestimate the load bearing capacity of the shear connector. 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 ny: 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 ny 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.The RFCS project “DISCCO” was supported by the grant agreement number RFSR-CT-2012-00030. Further, the authors gratefully acknowledge the support of ArcelorMittal Global R&D, Long Products Luxembourg.Vigneri, V.; Odenbreit, C.; Braun, M. (2018). Numerical evaluation of the plastic hinges developed in headed stud shear connectors in composite beams with profiled steel sheeting. En Proceedings of the 12th International Conference on Advances in Steel-Concrete Composite Structures. ASCCS 2018. Editorial Universitat Politècnica de València. 229-236. https://doi.org/10.4995/ASCCS2018.2018.7166OCS22923

Design models for predicting the resistance of headed studs in profiled sheeting

This paper presents the results from reliability analyses of the current Eurocode 4 (EN 1994-1-1) and AISC 360-16 design models for predicting the resistance of headed stud shear connectors within profiled steel sheeting, when the ribs are oriented transverse to the supporting beam. For comparison purposes, the performance of the alternative “Luxembourg” and “Stuttgart” model were also considered. From an initial database of 611 push-out tests, 269 cases were included in the study, which ensured that the results were valid over a wide range of geometrical and material properties. It was found that the current EN 1994-1-1 design rules deliver a corrected partial safety factor γM* of around 2.0, which is significantly higher than the target value 1.25. Moreover, 179 tests fell within the domain of the concrete-related failure design equation. Notwithstanding this, the EN 1994-1-1 equations provide satisfactory results for re-entrant profiled sheeting. The AISC 360-16 design equation for steel failure covers 263 of the tests in the database and delivers γM*≈2.0. Conversely, whilst the alternative “Stuttgart” model provides an improvement over the current codes, only a corrected partial safety factor of γM*=1.47 is achieved. Finally, the alternative “Luxembourg” design model was found to deliver the required target value, with a corrected partial safety factor γM* between 1.21 and 1.28. Given the fact that the Luxembourg design model is the only model that achieved the target values required by EN 1990, it is recommended as a potential candidate for inclusion within the second generation of Eurocodes

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

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

Technical Report LA19.E Rev. B. Headed studs in profiled steel sheeting transverse to the beam. Investigations on design resistance of headed stud shear connectors on the basis of the Final Draft of SC4.PT3 (April 2018)

The unsafety of current design rules for novel types of open-trough deck geometries for the resistance of headed studs in profiled steel sheeting is well known [1] and it was the main reason behind the nomination of CEN/TC250/SC4- Task SC4.T3: “Revised rules for shear connection in the presence of modern forms of profiled sheeting”. During the RFCS research project “DISCCO” (RFCS-CT-2012-00030) [1], a mechanical model was developed on the basis of a large literature study and previous studies [2, 3, 4, 5, 6] while the corresponding design equations were presented by CEN/TC250/SC4.PT3 and further enhanced during the Research Project “ShearCON” of University of Luxembourg. In order to let the current rules of EN 1994-1-1 6.6 (Eq.(2) and (3)) as unchanged as possible, the limits of its suitable field of applicability (Database B1) was investigated thoroughly by means of the statistical procedure of EN 1990 D.8 [7]. The newly proposed equations (Eq. (7) and (8)) apply only to the cases outside these limits (Database B2). In this way, the proposed solution is able to restore the level of safety to its initial value, so that the partial safety factor for the shear connection ϒV=1.25 is adequate. Conversely, the current situation (without including the new design equations) would need a much higher partial safety factor as shown below

Feasibility study on stub and slender veneer‐wrapped steel columns

The paper presents a newly developed steel-timber composite column, called “STIMBER-COL”, which is made of an inner hollow section wrapped by several veneer layers glued together. In addition to the well-known environmental benefits, the potential advantages at mechanical level are thoroughly discussed in consideration of the literature available. In view of the promising experimental results on steel-timber composite columns reported in recent studies, a foreseen experimental campaign of 5 stub and 3 slender columns is described along with the setup and instrumentation. Special emphasis is given to the manufacturing process which represents a challenging step in this feasibility study. The test results confirm that the veneer layers lead to a significant increase in stiffness and strength. The work is conducted in the frame of an applied research project to support more advanced research and the implementation of the market in the future.ISSN:2509-707

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

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

Headed studs in profiled steel sheeting transverse to the beam. Investigations on design resistance of headed stud shear connectors on the basis of the Final Draft of SC4.PT3 (April 2018)

The unsafety of current design rules for novel types of open-trough deck geometries for the resistance of headed studs in profiled steel sheeting is well known [1] and it was the main reason behind the nomination of CEN/TC250/SC4- Task SC4.T3: “Revised rules for shear connection in the presence of modern forms of profiled sheeting”. During the RFCS research project “DISCCO” (RFCS-CT-2012-00030) [1], a mechanical model was developed on the basis of a large literature study and previous studies [2, 3, 4, 5, 6] while the corresponding design equations were presented by CEN/TC250/SC4.PT3 and further enhanced during the Research Project “ShearCON” of University of Luxembourg. In order to let the current rules of EN 1994-1-1 6.6 (Eq.(2) and (3)) as unchanged as possible, the limits of its suitable field of applicability (Database B1) was investigated thoroughly by means of the statistical procedure of EN 1990 D.8 [7]. The newly proposed equations (Eq. (7) and (8)) apply only to the cases outside these limits (Database B2). In this way, the proposed solution is able to restore the level of safety to its initial value, so that the partial safety factor for the shear connection ϒV=1.25 is adequate. Conversely, the current situation (without including the new design equations) would need a much higher partial safety factor as shown below

Experimental study on the longitudinal shear transfer mechanisms and resistance in CSTC composite beams

This contribution presents an experimental study on composite steel truss in concrete (CSTC) beams consisting of prefabricated structural steel latticed girders embedded in concrete. Unlike typical composite beams with downstand steel profiles using headed stud shear connectors, CSTC beams are composed of straight and sinusoidally bent bars with a circular cross-section, in which the transfer of the longitudinal force is ensured via a mechanical interlock between the steel diagonals and the surrounding concrete slab. Because of the lack of specific tests, it is necessary to comprehend the local behaviour (stiffness, resistance and slip capacity) through new experimental investigations which support the development of a reliable design model able to predict the respective longitudinal shear resistance. This paper presents and discusses the setup and results of a wide experimental campaign of more than 30 push-out tests on CSTC beams. Different geometrical and mechanical parameters were varied in accordance with their typical range of application. Based on the experimental results, it was found that the shear transfer mechanism and resistance is governed by localized concrete failure combined with plastic bending deformation of the diagonal bars. The load-slip behaviour was found to be qualitatively comparable with headed stud shear connectors and the significant slip capacity, in most cases beyond 20 mm, indicates that the sinusoidal web bars lead to a shear transfer mechanism that may be considered to be ductile according to EN 1994-1-1. In addition, to isolate the local contribution to the resistance provided by the bars near the weld seams, the diagonal bars of some specimens were intentionally sawed off in some of the specimens, resulting in a “steel tooth”. The load carried by this isolated component was found to be about 58 % of the full longitudinal shear resistance. The experimental values of the resistance were finally used to calibrate statistically an analytical equation for predicting the design of longitudinal shear resistance in compliance with the reliability levels given in EN 1990. Additional considerations concerning the potential interaction with the vertical shear load capacity given by the diagonal bars were included in the final design proposal.ISSN:2352-012

On the load‐carrying behaviour of CSTC slim‐floor beams

Composite steel truss and concrete (CSTC) beams are steel-concrete composite structures mostly used as slim-floor systems in industrial buildings. The proposed paper focuses on the load-bearing behaviour of the so called NPS beam system as a specific type of CSTC beam. This system is made of a sinusoidal smooth steel truss welded to a steel plate, and embedded in cast-in-situ concrete. Unlike standard composite beams, NPS beams do not have dedicated shear connectors for transferring the longitudinal shear force from the steel part to the concrete. The shear connection between steel and concrete is enabled by the sinusoidal bar as an integrated part of the steel profile. The load-slip behaviour of the shear connections in NPS beams was recently investigated through push-out tests and appropriate design rules were proposed to predict their resistance. However, the longitudinal shear connection behaviour within the overall beam system is still not fully understood and requires further investigations. Furthermore, the ductility of composite slim floor systems depends strongly on their geometrical and mechanical properties. Strain-limited analyses provide more reliable design predictions, but typically still simplify the shear connection behaviour strongly. It is therefore reasonable to conduct full-scale experimental tests to investigate the structural behaviour at a cross-sectional and a global level. The presented work addresses those issues through preliminary strain-limited analyses and the description of an advanced measurement concept using fibre optical sensors for full-scale beam tests.ISSN:2509-707

Numerical study on design rules for minimum degree of shear connection in propped steel–concrete composite beams

ISSN:0141-029