Composite Floor System Research Articles

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.

Economical Design Comparison of Large-Span Composite Floor Systems with I Beams and Corrugated Web Beams

A comparative study of composite floor systems with I-beams and corrugated web beams is performed based on non-linear programming (NLP) algorithm. The optimization is conducted to find the most economical design with minimum steel consumption considering variables associated with the cross-sectional dimensions and multiple constraints from standards, specifications and engineering practices. Various parameters of live loads ranging from 2 to 10 kN/m2 and spans ranging from 20 to 100 m are considered. The optimization results reveal that composite floors with corrugated web beams have reasonable and economical cross-sections with less steel consumption, owing to the high performance of the corrugated web in shear resistance and stability. Further comparative studies show that composite floors with corrugated web beams are economically competitive for spans larger than 30 m with a steel saving of 20–60%, and composite floors with welded I-beams can be applicable for spans less than 30 m considering the simpler configuration and construction. In addition, a spatially structured cable-supported steel–concrete composite floor system is proposed and recommended for super-large-span floor structures considering the cost-effectiveness of the analyzed floor systems reduces as the span further increases.

Numerical Study on the Bending Resistance of Lightweight Built-Up Steel-Concrete Composite Beams

This paper investigates the bending resistance of an innovative lightweight composite floor system, LWT-FLOOR. The system consists of built-up cold-formed steel elements that are spot-welded and connected to the concrete slab using demountable shear connectors. As the system under investigation is new, the existing standards do not provide guidelines for calculating its bending resistance. This paper gives an overview of different analytical approaches and a comparison of calculated results using bending capacities from the numerical parametric study. Within the numerical parametric study, the influence of the height of the steel beam, the type and degree of shear connection, the connection between the steel elements, and the thickness of the corrugated web used for the bending capacity are investigated. Numerical results for the full shear connections resulted in lower bending capacities than the analytically calculated plastic bending resistances. However, numerically obtained bending capacities for partial shear connections were found to exceed the calculated characteristic non-linear bending resistances and bending resistances for partial shear connections. The obtained results will comprise the basis for further experimental tests, which will support the search for an optimal analytical approach for the bending resistance of the proposed composite system.

Reinforced cross-laminated timber-concrete composite floor systems

This paper presents full-scale experimental investigations on cross-laminated timber concrete composite (TCC) systems. The primary objective was to determine the stiffness, ultimate load-carrying capacity, and failure modes of TCC systems using three different shear connectors: self-tapping screws, steel kerf plates, and proprietary glued-in perforated steel plates. The secondary objective was to determine the effectiveness of shear reinforcement in the CLT panels. The TCC system was comprised of 245 mm thick, 7-ply CLT panels with a 150 mm concrete topping. A total of 24 half-span (4.6 m long) and 9 full-span (9.2 m long) CLT and TCC floor segments were tested under symmetric four-point bending as well as torsional bending. For all test series, the CLT panels were either unreinforced, or reinforced using self-tapping screws. The shear reinforcement increased rolling shear capacity which helped to avoid CLT shear failure. Adding the concrete topping increased the shear capacity by up to 167%. The tests showed that the floors with steel kerf plates exhibited the highest capacity and stiffness, while also being the most easy-to-install solution. The results from this research guided project-specific design decisions for “Limberlost Place”, a mass timber building for George Brown College, in Toronto, Canada.

Critical collapse deformation of 3-D steel frame with composite floor system

Determination of the CCD (critical collapse deformation) for frame structures is crucial to calculate their final collapse resistance due to a column loss. This paper studies the CCD of 3-D (three-dimensional) steel frame structure in an interior column loss. The work presented in this paper is an extension of previous work by authors on two-dimensional (2-D) steel frame, by further introducing the effects of concrete floor slab. The fracture of steel is considered by Bai-Wierzbicki model, in which the effects of Lode angle and stress triaxiality on fracture of steel are accounted for. The Bai-Wierzbicki model is imported into software ABAQUS by a user-defined subroutine. The CCDs of 2-D steel frame, 3-D steel bare frame, and 3-D steel frame with floor slab due to an interior column loss are compared. The effects of beam span, beam height, slab thickness, and slab aspect ratio on the CCD of 3-D steel frame are studied. For steel frame with different slab span-to-thickness ratios, explicit calculation formulae are established to calculate the CCD of steel frame. It is found that due to the existence of floor slab, the CCD of steel frame is significantly reduced. A larger span-to-depth ratio for steel beam ensures a greater CCD of steel frame. For a certain slab span-to-thickness ratio, the CCD-to-depth ratio of steel beam is almost linear against the span-to-depth ratio of steel beam. Moreover, the CCD of steel frame increases when the slab aspect ratio increases.

Experimental Assessment of Alternative Shear Connections in Cross-Laminated Timber-Concrete Floor Systems

New building code changes enable mass timber panels (MTP), including cross-laminated timber (CLT), to be used in moderate and tall buildings as a floor system, usually with a concrete topping. A floor system of CLT composite with a reinforced concrete topping slab can provide increased stiffness and strength, making the system more advantageous. Present connection methods used to produce composite action within timber-concrete composites (TCC) have limitations when considering constructability or performance. This study presents experimental results from four (4) shear connectors for CLT-concrete composite floor systems, including three developed for this study. The connectors included self-tapping screws (STS) at 45-degrees, a modified lag screw with an integral plate washer that bears on the CLT surface at installation, a steel angle anchored only at the end of the span, and an inverted-T steel section with stem perforations. Different tests were performed on the different connectors including individual fastener tests, push-off group tests, and full-scale one-way bending tests. The push-off group tests showed that the proposed washer-screw exhibited higher stiffness and strength than a conventional STS. The full-scale one-way bending testing showed that the STS specimen exhibited the lowest strength of the alternatives. The inverted-T section exhibited the highest stiffness, while the other three connections had similar stiffness to the STS.

Analytical Assessment of the Structural Behavior of a Specific Composite Floor System at Elevated Temperatures Using a Newly Developed Hybrid Intelligence Method

The aim of this paper is to study the performance of a composite floor system at different heat stages using artificial intelligence to derive a sustainable design and to select the most critical factors for a sustainable floor system at elevated temperatures. In a composite floor system, load bearing is due to composite action between steel and concrete materials which is achieved by using shear connectors. Although shear connectors play an important role in the performance of a composite floor system by transferring shear force from the concrete to the steel profile, if the composite floor system is exposed to high temperature conditions excessive deformations may reduce the shear-bearing capacity of the composite floor system. Therefore, in this paper, the slip response of angle shear connectors is evaluated by using artificial intelligence techniques to determine the performance of a composite floor system during high temperatures. Accordingly, authenticated experimental data on monotonic loading of a composite steel-concrete floor system in different heat stages were employed for analytical assessment. Moreover, an artificial neural network was developed with a fuzzy system (ANFIS) optimized by using a genetic algorithm (GA) and particle swarm optimization (PSO), namely the ANFIS-PSO-GA (ANPG) method. In addition, the results of the ANPG method were compared with those of an extreme learning machine (ELM) method and a radial basis function network (RBFN) method. The mechanical and geometrical properties of the shear connectors and the temperatures were included in the dataset. Based on the results, although the behavior of the composite floor system was accurately predicted by the three methods, the RBFN and ANPG methods represented the most accurate values for split-tensile load and slip prediction, respectively. Based on the numerical results, since the slip response had a rational relationship with the load and geometrical parameters, it was dramatically predictable. In addition, slip response and temperature were determined as the most critical factors affecting the shear-bearing capacity of the composite floor system at elevated temperatures.

Flexural behaviour of timber-concrete composite floor systems linearly supported at two edges

Timber-concrete composite (TCC) structures consist of thin concrete slabs connected by stud or bonding to glulam beams. They emerged as a valuable system with light-weight elements characterised by high strength and stiffness. However, the structural efficiency of real-scale TCC floors with an adhesive-based connection systems requires further investigation to confirm the promising results of small-scale experimental studies.To contribute to this investigation, this study conducts real-scale experiments on five timber-concrete composite floor specimens that are linearly supported at two edges. The flexural behaviour of the system is assessed using a four-point bending test, and its strength and displacement capacity are also tested. The study also provides insights on the strain profile and relative displacement of the system’s cross sections.The experimental results indicate that the composite structure has adequate mechanical behaviour that is characterised by a linear response up to failure, without relative displacement at the concrete–timber interface surface. The study confirms the potential of TCC floors as prefabricated construction elements, demonstrating that the system complies with standard performance requirements.

NUMERICAL ANALYSIS OF LOAD‐BEARING FIRE TEST FOR REINFORCED CONCRETE SLABS

AbstractA numerical analysis is conducted for the load‐bearing fire test of composite flooring systems composed of flat RC slabs and unprotected beams (beams with no fire protection covering), and the test results and numerical analysis results are compared. The main aim of the numerical analysis is to verify the accuracy of the numerical analysis approach as well as to analyse the stress distribution within the composite floor when the membrane functions as intended, the data for which are difficult to obtain from the load‐bearing fire test.

MEMBRANE ACTION OF REINFORCED CONCRETE SLABS IN FIRE

AbstractFor RC slabs supported in 2 ways, when deflection increases, membrane stress occurs within the cross section of the slab, and as a result the load‐bearing capacity of the slab is improved due to this membrane action. In this paper, the results of load‐bearing fire test are introduced that targets a composite flooring system composed of a flat RC slab in which two‐tier reinforcements are arranged and an unprotected beam. The RC slab to which the bending collapse load based on the yield‐line theory was given sustained load‐bearing capacity even after being subjected to 3 hours and more of standard fire heating.

Study on the load-carrying capacity of an innovative cold-formed steel floor system

To account for the higher structural ductility requirement and higher load-bearing capacity and stability requirements of floor-to-wall connections of mid-rise cold-formed steel (CFS) structures, an innovative CFS floor system with gridded beams and filler blocks (BB-based CFS floor system, where BB stands for “beams” and “blocks”, respectively) was first proposed. Then, experimental and refined numerical simulation studies were performed to investigate the flexural behaviour of the floor system. Afterwards, a simplified calculation method of the load-carrying capacity of the floor system was deduced based on its mechanical mechanism. The results show that (1) the deformation of the floorboard-to-beam screw connections and the relative buckling of the compression beam flange and adjacent web are the primary reasons for the nonlinear load-deflection relationship and bending failure of the floor system. (2) Compared with the existing CFS composite floor systems, the combination effect of each component in the BB-based CFS floor system prevented the beams from unstable failure after losing the restraint of floorboards, thereby effectively improving the load-carrying capacity and nondeformability of the floor system. (3) After decomposing the BB-based CFS floor system into composite floor beams, the load-carrying capacities of the floor system can be determined simply according to the cumulative flexural bearing capacities of these composite floor beams based on plasticity theory, the relative errors between the deduced load-carrying capacities and the test results and simulated results of different BB-based CFS floor systems are within 10%, and the calculated results are relatively safe.

Shear connection performance of cold-formed steel and plywood composite flooring systems: Experimental and numerical investigation

This study carries out numerical and experimental investigation on shear connection performance of flooring systems comprising of cold-formed steel joists and engineered plywood panels. A 3-D finite element model has been developed using ANSYS software which considers the nonlinear behaviour and damage of plywood panels using a maximum stress-based criterion incorporated in the FE model. The yielding behaviour of steel joists and fasteners (screws and bolts) is defined as a multilinear plastic hardening material model defined in ANSYS software. The FE model was validated against the experimental results obtained from push-out tests conducted on specimens utilising different connection arrangements. The validated FE models showed a good agreement with the experimental results of the push-out tests in terms of load-slip behaviour, ultimate peak capacity, and failure modes. Finally, the validated FE models are utilised to perform a parametric study that investigates the effect of varying various parameters, including diameter and yield strength of self-drilling screws, the thickness of plywood panels, value of friction coefficient, and the ratio of fastener diameter to the joist thickness, on the initial stiffness, failure mode and ultimate load capacity of the cold-formed steel and plywood composite connections.

Development of composite action in a new long-span timber composite floor: Full-scale experiment and analytical approach

The mechanical performance of timber composite floor elements significantly depends on the composite action among different components. The composite action in conventional timber floors with a span limit of 8–9 m has been studied during the last two decades. For long-span timber composite floors with a span over 12 m, how to develop an efficient composite action is still an open question. In this study, the composite action in a long-span timber composite floor system was investigated. The floor system integrates LVL (Laminated Veneer Lumber) panels and GLT (Glued Laminated Timber) beams to form a continuous box girder structure. Various types of inclined screw connections combining LVL and GLT for a composite action were tested. One configuration was chosen to make the 12 m composite floors and four-point bending tests were conducted at different screw spacings. The degree of composite action was evaluated based on the observed overall bending stiffness and relative displacements between different components. The composite action in timber composite floors with concrete topping was also studied. An analytical approach based on Gamma method was adopted to estimate the effective bending stiffness of the composite floor. The findings in this study showed that bending stiffness over 26,000 × 109N·mm2 and composite action over 50 % can be achieved with a small number of screws. Reducing the screw spacing and adding concrete topping would further improve the overall stiffness. The predictions of the analytical model match well with the tested results for both the configurations with and without concrete topping.

Maximum displacement prediction of composite floor system under falling impact

Analytical and numerical investigations on the maximum displacement of the steel-concrete composite floor system subjected to falling impact are presented in this paper. Explicit formulae are established to compute the floor maximum displacement under impacts with different kinetic energy transfer ratios. Parametric analyses are conducted to study the influence of impactor mass, impact height, floor longitudinal span, floor thickness, rebar diameter, beam depth, and coefficient of restitution on the maximum displacement of floor. Associated practical recommendations are also proposed for determining the maximum displacement of floor under falling impact. It is found that in fully elastic impact, the maximum displacement is highly sensitive to the impact height, whereas in fully plastic impact, the value is significantly affected by the impactor mass. The upper-bound estimation of the displacement can be achieved by using fully elastic impact model. However, fully plastic impact model should be adopted when the impactor mass increases to more than 30 % of the total mass of the floor.

Flexural behaviour of a new timber-concrete composite structural flooring system. Full scale testing

Timber-concrete composite systems are a high-performance alternative for building floors, of great interest in the current context of environmental concerns. Looking for a more eco-friendly solution, the paper presents a new flooring system with a wood-concrete connection that does not require adhesives or special metal elements. Four-point bending tests were performed on TCC flooring samples with a span of 6.0, 7.2 and 8.4 m. Its cross section was a prefabricated piece in the shape of an inverted T made up of a lower glulam flange, glued together with a central plywood rib with aligned holes in its upper part that go through the entire thickness of the plywood. The set was completed with a top layer of poured-in-place concrete. The connection between both materials is achieved by penetrating the concrete into the rib holes. Additionally, corrugated steel bars were placed through said holes to achieve ductile behaviour. In all cases, a slenderness ratio of L/24 was used. The experimental results showed that the lowest value of ultimate load obtained was 4.3 times higher than the total service load estimated for a building for public use (9 kN/m2). The maximum deflection of the total load was between L/573 and L/709 for the loads corresponding to a building for public use (9 kN/m2) and between L/1069 and L/1340 for the case of residential type building (5 kN/m2). An analysis of the effects of vibrations in the service limit state in relation to user comfort has been included. The results indicate that the system satisfies the requirements for the intended uses.Consequently, the proposed solution shows its effectiveness both in terms of strength and stiffness for the construction of light floors, being easy to build and having high performance.

Behaviour and design of double angle beam-column connection in fire conditions

The behaviour of composite floor systems in fire depends significantly on the performance of connections supporting the beam. This paper discusses the performance of double-angle shear connections under fire conditions investigated using numerical analyses and suggests changes to connection design and detailing for their improved fire performance. Finite element models are used to perform sequentially coupled, heat transfer and stress analyses of composite beams with end connections. The analysis technique is validated against several experimental studies. Two major triggers for connection failure in fire are identified: (i) excessive deformation following web buckling during the heating phase and (ii) contraction of the beam during the cooling phase. It is observed that the flexibility of angles used in the connection causes prying action and leads to a localized increase in the weld force demand, which increases the likelihood of a premature failure of the welded joint. The beams that have bottom flange coped at the ends are found to be more susceptible to web buckling during the heating phase. The web buckling can be prevented by using stiffened angles. The failure during the cooling phase can be prevented by using slotted holes.

Experimental Investigation on Fire Behavior and Quantitative Restraint Forces of Steel–Concrete Composite Floor Systems

Experimental Investigation on Fire Behavior and Quantitative Restraint Forces of Steel–Concrete Composite Floor Systems

Experimental study on monotonic and cyclic behaviour of deconstructable beam-to-column composite joints

Deconstructable composite beams, in which bolted connectors are introduced between prefabricated concrete slabs and steel beams, offer promising demolition efficiency. Compared with conventional cast-in-situ composite floor systems, such novel composite beams provide favourable economic performance and sustainability by considerably improving the recyclability of structural components. In this study, four full-scale deconstructable beam-to-column composite joints with deconstructable beams were designed, manufactured, and tested under monotonic and cyclic loading. The structural performances—crack pattern, failure mode, strain distribution and moment–rotation response, energy dissipation, and deterioration evolution—were investigated thoroughly. The effects of the loading scheme and a force-transmission sleeve on the structural performances were simultaneously studied. The moment–rotation responses showed that the composite joints possess outstanding strength, rotation capacity, ductility, and energy dissipation ability. The deformability satisfies the minimum rotation capacity specified by Eurocodes 3 and 4. Strain analysis demonstrated that the composite beams provide favourable composite shear interactions. The installation of the force-transmission sleeve improved the strength of a composite joint owing to the incorporation of steel bars split by the column into the moment-resisting system. These deconstructable composite joints can achieve favourable deconstructability and demolition efficiency at the termination of service life, and thus, serve as novel structural members.

Numerical Assessment of Steel and Concrete Composite Beams with Cold Formed Members

AbstractAlthough steel and concrete composite floors are generally constructed with hot‐rolled steel, there are several benefits of using cold‐formed steel (CFS) in these structures, such as lightness and less susceptibility to corrosion. The main disadvantage of using CFS in the steel beams is its connection to concrete, since the CFS members are thin and commonly used connectors are not suitable for it. This research studied a composite flooring system, which includes an innovative disposition of the CFS profiles and a connection system adapted to CFS elements. The CFS beam is composed of C‐shaped profiles ‐ forming a U‐shape that is filled with concrete, and may be associated with a profiled steel sheeting. The edges of the steel profile placed on the bottom of the beam are embedded in the concrete section, enhancing the composite action. This work was conducted by analytical assessment and numerical modelling based on FEM. The study was developed to verify if the proposed flooring system can be designed for different loading levels and geometrical dimensions and to evaluate its capacity to transfer shear stresses between the CFS and concrete without the use of conventional shear connectors.

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.