Slim Floor Research Articles

Composite Delta Beam for Slim Floor Construction

Abstract: The structural behaviour of the composite Flush Beam for slim floor as a whole has been investigated. The deformation behaviour of the structural members Steel beams with trapezoidal cross-sections and specially punched webs were developed as composite beams in slim floors. The estimation of the flexural stiffness and bending capacity of composite slim beams is rather complicated, because the influence of many factors should be taken into account. These factors include variable section dimensions, Profile of the beam, stiffness of the beam and interaction between steel and concrete. In this paper, analytical investigations have been conducted to investigate the deflection behaviour of Flush beam specimens under monotonic loading. A design procedure is developed for composite slim floor Flush beams based on cross-sectional analysis and the flexural properties of the slim floor beams are evaluated. From the analytical investigation it was found that the deflection of delta beam is 48% less than the conventional I-beam More over the stiffness of the Delta beam is 49.8% higher than the I-beam

Structural capacity of a composite slim-floor beam with hollow steel tube shear connectors

A slim-floor composite beam’s structural performance relies on the composite action provided by shear connectors. However, the information on the performance of composite slim-floor beam with HSTs connectors in flexural in term of moment capacity, shear interaction and ductility still needs to be clarified. Thus, six specimens of the composite beams with square and rectangular HSTs with two different beam sections, I and inverted T, were tested. The main failure was found to be concrete crushing in the area of the connectors. HST connectors prevented the concrete slab from uplifting, particularly in the specimens without a top flange. Subsequently, this increased moment capacity to 230% and 152% for inverted T and I-beam sections, respectively. Furthermore, ductility behavior was also improved and met EC4 requirements. The degree of shear interaction was increased from 0.4 up to 0.9 compared to the beam without HST. The predicted results from the suggested procedure to estimate moment capacity agreed well with the experimental results, with a maximum difference of 7% in the I-section specimen. In contrast, the predicted value for the inverted T specimen overestimates about 26%. Overall, the beam with the HST shear connector significantly improved the flexural performance of the composite slim floor beam.

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

AbstractComposite 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.

Innovation of Shear Connectors in Slim Floor Beam Construction

Composite slim floor systems are increasingly applied in the construction industry. Therefore, several experimental and numerical studies have been conducted to investigate the composite flooring systems and examine the various details that may affect the production of composite floors. This review paper summarises some important developments of composite slim floor beams, such as the type of steel beam cross section and shear connectors used, presenting essential results and important notes from various studies. The fundamental structural elements and the contribution of conducted studies towards improving the shear capacity of composite beams in enhancing the general structural behaviour were also described. Finally, the paper concludes with the potential of a deeper investigation of some issues that accompany the application of certain types of shear connects or steel shapes used to improve the composite slim floor system so that the improvement construction industry may make the most out of using composite construction techniques.

Numerical analysis of composite slim-floor beams

Abstract In this research work existing laboratory tests of slim floor beams with solid monolithic concrete slab were modeled and analyzed using GID and Atena software. After validating the advanced finite element model with the test results of the international literature, structural parameters were analyzed with the aim to study their influence on the load bearing and deformation capacity of the beams. The parameters were related to the geometric of the beam: size of web openings and top concrete cover. With these results conclusion can be noticed that focusing on the optimal arrangement of the geometrical parameters of the composite beam could lead to better structural behavior with more economical solutions.

Hybrid slim floor structures for a more sustainable future

AbstractHybrid structures are a current trend in the building industry that greatly increase the sustainability. Building with hybrid structures means in general combining different materials, such as wood, concrete, or steel to generate new properties that cannot be achieved by usage of the individual materials itself. When using hybrid structures, buildings of all types and usages can be built very quickly and flexibly. The same can be achieved with prefabricated systems used for slim floor structures. By combining hybrid and slim floor structures, not only the CO2 emissions will be lower, because materials that accommodate low emissions such as wood are used, even the building height can be reduced and, as a result, the heating and cooling costs will be lower. In addition, such structures can be demounted again, when the lifecycle of a building ends and reused in the same or a different function. These are just a few aspects and advantages of hybrid slim floor structures that will be examined in more detail below.

Shear capacity of prestressed hollow core slabs in flexible support using computational modelling

The aim of the present investigation is to analyse the shear capacity of hollow core slabs supported on shallow beams, so-called slim floor construction, using a computational modelling performed with the DIANA software package. The finite element models were calibrated using two full-scale tests on a slim floor system and tests on single slabs on rigid supports reported in the literature. Besides, the numerical analyses were compared with analytical equations available to predict the shear capacity of hollow core slabs on both rigid and flexible supports. The non-linear three-dimensional finite element model agreed well with the results from full-scale tests on the slim floor system. A parametric study was performed to evaluate the influence of the infill at the ends of the hollow cores and the support stiffness of the steel beams on the shear capacity of the slabs. The numerical results confirm the influence of flexible supports on the shear capacity of hollow core slabs but reveal a marginal influence of the infill of the hollow cores. For hollow core slabs with oblong-shaped openings, the shear capacity of the slabs on the flexible supports was reduced when the hollow cores were filled. From the parametric study, design models available in the literature for hollow core slabs on flexible supports were tested and modified.

Numerical model validation of non-composite slim floor beam subjected to fire

Abstract Compared to traditional composite steel-concrete beams, where the concrete slab is supported by the top flange of a steel profile, in slim floor systems, the beam is integrated into the height of the concrete slab. These configurations are popular due to their cost-effectiveness and fire performance. However, fire design requires advanced calculation models, as Eurocodes do not provide a simplified method for the analysis of these types of beams when exposed to fire. The validation of the numerical models is an important issue for researchers, designers, software developers, and authorities. The European Standard for the fire design of composite steel and concrete structures, EN 1994-1-2, states that advanced calculation models must be validated against experimental test results. The paper presents the validation of a numerical model, for the thermal and mechanical analysis of slim floor beams, using SAFIR software. SAFIR is a special purpose computer program, based on the Finite Element Method, developed for the analysis of structures under elevated temperature conditions. The model is validated against an existing experimental fire test, available in the literature. The temperatures on the cross-section and the vertical beam displacements obtained numerically are reproducing very well the experimental results.

Shear forces transfer in steel-concrete slim floor with circular web opening and PCHCS

An experimental study was developed to investigate the mechanisms responsible for the transfer of shear forces at the steel-concrete interface in slim floor beams with circular web openings and precast hollow core slab (PCHCS). For this purpose, four specimens were made and subjected to push-out test. The presence of the steel bar through the opening, the concrete compressive strength and the diameter of the steel bar were studied. It was observed that the presence of the steel bar contributed significantly to both the resistance of the connection and for the reduction of the relative slip values of steel-concrete. While the specimen without steel bar presented a post-peak behavior with a drop of resistant capacity, in the specimens with steel bar the load-slip relationship was quite ductile. The variation in steel bar diameter and concrete strength influenced both load-slip relationship and resistant capacity. It was observed that regardless of the presence of steel bar, until the concrete dowel rupture, the load-slip behavior of the specimens with and without steel bar was almost identical. The experimental results were compared to analytical models proposed by other researchers. However, none of the analytical models found in the literature were able to satisfactorily represent the resistant capacity of the specimens with and without steel bar. A good estimate of the theoretical results was obtained using the friction-shear theory for concrete corbels.

Analytical Method for the Bending Resistance of Slim Floor Beams with Asymmetric Double-T Steel Section under ISO Fire

The slim floor beams, characterized by the steel profile embedded in the concrete slab, may be found in different configurations, based on the shape of the steel profile cross-section, which can vary from a rectangular to double-T section. While the most common shape used nowadays is the double-T cross-section, the Eurocodes do not provide a simplified method for the fire resistance assessment. The literature offers a simplified method for computation of bending resistance under elevated temperature, based on existing research on thermal models, and was validated for a particular type of slim floor beams (SFB). The current study extends the scope of application of this method, for different types of slim floor beam, which include an asymmetric double-T steel cross-section. The objective was reached through a numerical procedure, by analyzing 162 configurations subjected to four different fire requirements (R30, R60, R90, R120), resulting in a total of 648 analyses, performed with a validated numerical model in SAFIR software. The results in terms of bending resistance showed that the simplified method represents a strong tool for the fire design of slim floor beams.

Experimental study of shear transfer in slim floor systems using precast concrete hollow core slabs and steel beam with web circular opening

Abstract Steel-concrete slim flooring system using precast concrete hollow core slabs and steel beam with web openings is an innovative construction system designed to combine the high bending resistance of both precast prestressed hollow core slabs and steel beam with web openings. This system can provide floor systems with a minimum constructional depth in comparison with ordinary composite floors. The aim of this study was to evaluate in an exploratory way the shear transferring mechanism between the steel beam with circular web opening and the precast hollow-concrete slab. The shear connection is formed by in-situ concrete passes through the web openings and infill the voids of the precast slabs. One push-out test was conducted to investigate the shear transferring mechanism of shear connection and the experimental results were compared to analytical methods. The shear resistance of the shear connection was predicted with good accurate by analytical methods.

Finite Element Modelling for Structural Performance of Slim Floors in Fire and Influence of Protection Materials

Slim floor systems are very common nowadays and various types are currently being used for the construction of high-rise buildings and car parks. Concrete in slim floor beams encases the steel beam section which helps to improve their fire resistance. Despite their higher fire resistance, several fire protection materials like intumescent coatings are often used to achieve a higher fire resistance where desired. The thermal properties and behaviour of various intumescent coating materials were previously studied through experimental investigations. This paper presents finite element analyses to simulate the response of unprotected and protected slim floor beams in fire using different simulation tools. For this purpose, fire tests conducted on unprotected slim floor beams and intumescent coating materials are modelled using research and commercial software. Results from the analyses are compared and verified with the available test data. These validated models are later combined to study the behaviour of protected slim floor beams in fire. Results from the study show that the research and the commercial software replicate the behaviour of slim floor beams and protection materials with good accuracy. Due to the presence of the intumescent coating, the protected slim floor beams displayed a better fire resistance as the temperature of the steel part remained below 400 °C even after 60-min of standard heating. The protected slim floor beams continued to support the external loads even after 120 min of heating.

Parametric study on the structural behaviour of composite slim floors with hollow-core slabs

Steel-concrete composite structures and precast concrete elements have a common prefabrication process and allow fast construction. The use of hollow-core slabs associated with composite floors can be advantageous. However, there are few studies on the subject, impeding the application of such systems. In this paper, a numerical model representing the considered system using the FE (finite element)-based software DIANA is developed. The results of an experimental test were also presented in Souza (2016) and were used to validate the model. Comparisons between the numerical and test results were performed in terms of the load versus displacement, load versus slip, and load versus strain curves, showing satisfactory agreement. In addition, a wide parametric study was performed, evaluating the influence of several parameters on the behaviour of the composite system: The strength of the steel beam, thickness of the web, thickness and width of the bottom flange of the steel beam and concrete cover thickness on top of the beam. The results indicated a great influence of the steel strength and the thickness of the bottom flange of the steel beam on the capacity of the composite floor. The remaining parameters had limited influences on the results.

Comparison of HST and WO Shear Connector Behaviour in Composite Slim Floor

AbstractComposite steel‐concrete slim floor construction is an economical floor system proposing minimum floor depth and fast construction besides architecture requirements. In this system, the concrete slab is supported on the lower flange of the steel beam using either in‐situ or pre‐cast technique, which eliminates the use of the down‐stand beam, hence giving a flat look. Hollow steel tube (HST) shear connector is proposed to avoid premature failure that could occur in concrete and steel beam web when the web openings (WO) connectors were used. In this paper, the comparison of push‐out test results between HST and WO to evaluate their ultimate shear load and ductility performance of these type of connectors. The varied parameters were the concrete compressive strength and shape of the HST and WO; the circular, rectangular and square. The results showed that the circular and square HST connectors achieved shear capacities 6.3 and 8.0 times higher than those with the WO type, respectively. Furthermore, the ductility of the specimens increased by 3‐4 times when the HST was used compared to WO. It shows that providing the HST significantly improved its ultimate shear load and ductility performance compared to WO.

Shallow composite floor beams – Proposal of a simplified analytical method for standard fire rating

AbstractShallow composite floor beams are a widely accepted solution for office, residential and other types of buildings. In most of their applications a standard fire resistance between R30 to R120 is required. Several fire tests were carried out in different laboratories over the last decades with various structural configurations, showing that this structural solution exhibits an integrated fire resistance without additional fire protection. In the frame of various programs, extensive research has been done on the fire behavior, completed by numerical simulations. Several scientists have proposed analytical methods to assess the resistance. Nevertheless, the Eurocode does not contain a method for assessing the standard fire resistance of composite shallow floor beams. This paper presents a simplified analytical method to determine the sagging moment resistance of Slim Floor Beams (SFB – being composed by a rolled section (or equivalent) with a wider plate welded below the bottom flange) under standard fire exposure. First, an FE model has been developed and validated on experimental tests. Afterwards, a parametric study covering various geometrical configurations and material choices has been performed. An analytical model for determining the sagging moment resistance is proposed and validated by comparison with results obtained by numerical simulation.

Experimental and numerical investigations on slim floor beams exposed to fire

Slim floor systems possess favourable thermal and thermo-mechanical behaviour in comparison with the traditional steel-concrete composite beams. Despite a recent surge in their usage in the construction sector, there is limited research on their performance at elevated temperatures. Due to limited investigations, there is a lack of fire design guidance for slim floor beams in major structural design codes. This study addresses the response of slim floor systems at elevated temperatures through experimental and analytical investigations. The experimental work consists of fire tests to study the thermo-mechanical response of SFBs in standard fire conditions. In addition to their thermo-mechanical response in fire, the efficiency of the rebars as an aid to enhance their fire resistance being an alternative to fire protection materials is also investigated. The test results show that the fire resistance of slim floor beams is significantly higher than the traditional steel-concrete composite beams due to the thermal gradient resulting from the concrete encasement. Further, the presence of longitudinal steel rebars enhances the fire resistance of SFBs significantly as they add to the flexural resistance of SFBs. During the tests, additional fire resistance of 79 min was achieved by the aid of steel rebars, a useful alternative to the fire protection materials which have been found to be toxic to the environment. Keeping in view the useful contribution of the steel rebars, a sensitive study was conducted using the finite element modelling to analyse the influence of their size and positioning on the fire resistance of the slim floor beams. Finite element modelling was later used to conduct a parametric study to analyse the influence of the degree of utilization on the response of slim floor beams exposed to standard fire. Degree of utilization represents the ratio between the applied load during a fire limit state and the capacity of the structural member at the ambient temperatures. The results from the parametric study were used to develop a simple design methodology by relating the degree of utilization and the average critical temperatures. Due to lack of fire design guidance in Eurocode 4, engineers usually use the design guidance proposed in Eurocode 3 which produces conservative results if applied to perform the fire design of slim floor beams as they have been developed for steel and traditional composite beams. The proposed methodology during this study is similar to that available in the Eurocodes for steel and composite beams but is developed specifically for the fire design of slim floor beams.

Prestressed hollow core slabs for topped slim floors – Theory and research of the shear capacity

This research paper discusses the influence of the flexibility of girders in Slim Floor structures on the reduced load capacity of prestressed HC slabs. The current state of knowledge in the field of the transverse behaviour of hollow core slabs is presented. Contradictory information provided in the literature as well as the computational comparative analysis of the existing theoretical models has demonstrated the need for better recognition of the issue of the effect of reinforced concrete topping layer on the load capacity of HC slabs. The paper includes the presentation of experimental tests, the purpose of which was to reproduce the actual work conditions of hollow core slabs depending on their location on the floor and the numerical analyses supplemented these studies. As a result of the conducted tests and analyses, it was found that the increased flexibility of the support beam resulted in an adverse change in the stress state of the hollow core slab, which may lead to the exceedance of the limit state of shear capacity, while laying an additional layer of structural topping on precast hollow core slabs significantly increased the shear capacity of the floor, and thus safety of the structure. The research also indicates that in all the tested topped elements full composite action up to the failure was shown.

Ultimate flexural strength analysis of composite slim floor beam

This paper presents a new type of composite slim floor beam, determined by combining the results of an experimental study and theoretical analysis of the ultimate flexural strength of slim floor beams. The shear connectors play a significant role in the mechanical properties of this type of composite slim floor beam, because the precast concrete slab is laid on the bottom flange of the steel section and because the upper portion of the steel beam is encased in the cast-in-place concrete slab. To investigate the ultimate flexural strength, three specimens, which included headed studs, transverse steel bar shear connectors and no shear connectors, were tested. Additionally, a detailed numerical analysis was performed to verify the experimental results, which indicated that a higher-strength steel beam and thicker concrete slab can effectively enhance the stiffness and flexural capacity of the composite slim floor beam. Based on plastic mechanics and limit analysis theory, a calculation method was derived to estimate the ultimate flexural strength of a composite slim floor beam, and a comparison between the calculation and experimental results shows that the theoretical results exhibit good agreement with the experimental results, and the proposed analysis method can be used in future studies to gain a better understanding of the ultimate flexural strength of composite slim floor beams.

Experimental and numerical investigation of the flexural behavior of shallow floor composite beams

This article summarizes a research campaign on the flexural behavior of a certain type of slim floor beam, generally known as Deltabeam. Seven (7) full-scale composite specimens with various cross-sections were tested under three-point sagging bending up to large displacements to test the robustness of the system. Experimental load–displacement curves, slip values and damage patterns are reported and compared with those obtained from non-linear FE analyses using the finite element analysis code ABAQUS. The tests showed that the ductility and robustness of beams, which are important properties for the design of flexural members, depend not only on the classification of the steel plated parts under compression, but also on the ability of the concrete section outside the steel beam to sustain large strains without stress reduction. The importance of appropriate detailing, and especially confinement of the concrete, and its influence on the performance of Shallow Floor-beams under large displacements is revealed by the results.

Numerical investigation on slim floors: comparative analysis of ASB and CoSFB typologies

abstract: Innovative composite structures have been intensively studied towards meeting the demands of civil construction. An example of such structures is slim floor, comprised of concrete or composite slabs positioned at the height of steel beams, reducing the total height of the floor. In Brazil, studies on this system are still in early stages, and due to the lack of both experience and national normative codes, it is hardly used in civil construction. Given the possible combinations between concrete slabs and steel beams, the system exhibits different typologies. This article reports a numerical investigation on two typologies of slim floor, namely Asymmetric Slimflor Beam (ASB), composed of an asymmetric I beam, and Composite Slim-Floor Beam (CoSFB), comprised of an asymmetric beam with small openings at the top of its web. Nonlinear numerical models of ASB and CoSFB typologies were developed by Finite Element-based software ABAQUS®. The models were calibrated with the use of experimental studies from the literature, and showed high accuracy and good results. After calibration, the materials properties and geometric dimensions of the models, such as height and thickness, were standardized for a comparison of the typologies. The comparative analysis showed the particular characteristics of CoSFB promoted higher stiffness and flexural capacity compared to ASB, and a parametric analysis evaluated the influence of steel and concrete parameters on the flexural behavior of the typologies. The parametric study revealed the steel parameters exerted a more substantial influence on the slim floors behavior than the concrete ones.