Steel-concrete Composite Floor Systems Research Articles

Essential Load-Bearing Characteristics of Steel–Concrete Composite Floor System in Fire Revealed by Structural Stressing State Theory

Essential Load-Bearing Characteristics of Steel–Concrete Composite Floor System in Fire Revealed by Structural Stressing State Theory

Numerical analysis of full-scale structural fire tests on composite floor systems

Recent experiments conducted at the NIST examined steel-concrete composite floor systems designed per U.S. practice under standard fire. The first experiment designed per prescriptive provisions for a 2-h fire rating with 60 mm2/m of reinforcement, developed a central breach integrity failure after approximately 1 h of exposure. The second and third experiments, designed with 230 mm2/m of reinforcement, with the third one omitting the fire protection on the central steel beam, showed no failure within 2 h. This paper describes a numerical investigation to gain further insights into the fire behavior of the composite systems tested in these experiments. Nonlinear finite element models were validated against the tests. Simulation of the first test shows concrete damage and rebar fracture in the hogging moment area corresponding with the cracks observed experimentally. Simulation of the third test captures the development of tensile membrane action, confirming the redistribution from the unprotected secondary steel member to the floor reinforcing steel. A sensitivity analysis allows identifying the minimum reinforcement steel for protected and unprotected central beams configurations. The results can support improvements of the fire requirements in the U.S. codes as well as application of performance-based structural fire design for composite structures.

Optimal Design of a Novel Large-Span Cable-Supported Steel–Concrete Composite Floor System

This paper optimizes the design of a novel large-span cable-supported steel–concrete composite floor system in a simply supported single-span, single-strut configuration, aiming for cost-effective solutions and minimal steel consumption. The optimization considers various cross-sectional dimensions, adhering to building standards and engineering practices, and is based on a non-linear programming (NLP) algorithm. Parameters of live loads ranging from 2 to 10 kN/m2 and spans from 20 to 100 m are considered. The optimization results show that cable-supported composite floors with a single strut exhibit robust economic feasibility for spans of less than 80 m and live loads under 8 kN/m2. Compared to conventional composite floors with welded I-beams, the cable-supported system offers more cost-effective cross-sections and reduces steel consumption. The savings in economically equivalent steel consumption range from 20% to 60%. Discussion on the area ratio of cables to steel beam in the optimal cross-section reveals that the secondary load-bearing system (i.e., bending of the main beam with an effective span length of L/2) may require more steel in cases of ultra-large spans. Therefore, the economical efficiency of cable-supported composite beams with multiple struts and smaller effective span lengths warrants further exploration in future studies.

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.

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.

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

Innovative Lightweight Cold-Formed Steel-Concrete Composite Floor System – LWT-FLOOR project

To provide the foundations for economic and social prosperity, countries worldwide need to be making a term investment in their building assets. However, there is a lack of a systematic approach, such as manufacturing innovations, to maximize the values of building components and materials in its entire lifecycle. Steel-concrete composite floor systems are one of the most cost-effective construction systems for multi-storey steel buildings because they combine structural efficiency with the speed of construction. These advantages depend on the efficiency of combining steel and concrete structural elements to avoid their inherent disadvantages. This paper presents a solution that integrates state-of-the-art knowledge in new, fast and productive spot-welding technology and innovative cold-formed steel-concrete composite solutions. The solution proposes a new construction method as a combination of built- up cold-formed steel members and cast-in-place concrete slab. The proposed floor system offers key benefits in terms of a high degree of prefabrication, reusability and long spanning capability.

Experimental study on fire resistance of a full-scale composite floor assembly in a two-story steel framed building

PurposeThe purpose of this paper is to report the first of four planned fire experiments on the 9.1 × 6.1 m steel composite floor assembly as part of the two-story steel framed building constructed at the National Fire Research Laboratory.Design/methodology/approachThe fire experiment was aimed to quantify the fire resistance and behavior of full-scale steel–concrete composite floor systems commonly built in the USA. The test floor assembly, designed and constructed for the 2-h fire resistance rating, was tested to failure under a natural gas fueled compartment fire and simultaneously applied mechanical loads.FindingsAlthough the protected steel beams and girders achieved matching or superior performance compared to the prescribed limits of temperatures and displacements used in standard fire testing, the composite slab developed a central breach approximately at a half of the specified rating period. A minimum area of the shrinkage reinforcement (60 mm2/m) currently permitted in the US construction practice may be insufficient to maintain structural integrity of a full-scale composite floor system under the 2-h standard fire exposure.Originality/valueThis work was the first-of-kind fire experiment conducted in the USA to study the full system-level structural performance of a composite floor system subjected to compartment fire using natural gas as fuel to mimic a standard fire environment.

Structural response of steel-concrete composite floor systems under traveling fires

An investigation was carried out to examine the structural response of two steel-concrete composite floor system under traveling fires. The thermal-mechanical analyses were performed using the finite element software ABAQUS, where the traveling fire exposures were defined using the improved Traveling Fires Methodology. Essential factors influencing the fire resistance of the composite floor systems, namely the fire rating and fire protection scheme of the passive fire protection were varied in this study. The composite floor systems were also exposed to an ASTM E119 standard fire and two natural fire exposures applied to a corner compartment. The results showed that fire insulations derived from prescriptive approaches may not provide adequate safety under traveling fires. Through a performance-based design procedure, improved performance under traveling fires was achieved through better allocation of the fire protection. Specifically, insulation from the interior floor beams were removed and applied to the girders and exterior floor beams. This fire safety solution is economical when compared to the simultaneous increase of fire protection of all floor beams and girders, typical of a prescriptive design approach.

Hybridization of metaheuristic algorithms with adaptive neuro-fuzzy inference system to predict load-slip behavior of angle shear connectors at elevated temperatures

Steel-Concrete Composite floor systems are one of the essential components in the construction industry. Recent studies have shown that fire-induced problems damage shear connectors and change the behavior of composite systems. To predict the performance of connectors, experimental tests are generally conducted at elevated temperatures or fire conditions. However, these tests need plenty of time, cost, and effort. This paper aims to propose a soft computing (SC) approach to predict the behavior of angle shear connectors at elevated temperatures. For this purpose, an adaptive neuro-fuzzy inference system (ANFIS), a particle swarm optimization (PSO) algorithm, and a genetic algorithm (GA) are hybridized and a novel ANFIS-PSO-GA model is proposed. To evaluate the performance of the ANFIS-PSO-GA model, a radial basis function network (RBFN) along with an extreme learning machine (ELM) are also developed. Finally, the performance of the ANFIS-PSO-GA, RBFN, and ELM are compared in the terms of different statistical indicators. The results of the paper show that the SC approach is applicable in the behavior prediction of angle connectors at elevated temperatures. Besides, it was concluded that the ANFIS-PSO-GA model can provide better estimations of load and slip in comparison with those of RBFN and ELM models.

Collapse testing of steel-concrete composite floor systems under an exterior-column-removal scenario

To evaluate the influence of openings in floor slabs on the collapse performance of steel-concrete composite floor (SCCF) systems, 2 one-third scale 1 × 2 bay SCCF substructures were fabricated and tested under static load up to final collapse in an exterior-column-removal scenario. The experimental results indicated that arch-shaped and radial cracks emerged on the top and bottom surfaces of the floor slab, respectively, for the SCCF substructure without openings in the floor slabs. Meanwhile, local buckling of the steel girders at the beam ends successively occurred during the loading procedure. As for the SCCF system with openings in the floor slabs, the crack distribution appeared more irregular, and torsion of the spandrel beam became prominent because of the discontinuity of the floor slab. The ultimate collapse resistance and the corresponding displacement of the failed column for the substructure with openings in the floor slabs were about 0.85 and 0.55 times as large as those of the substructure without openings. Owing to the existence of the openings, the tensile membrane action in the floor slab was weakened prominently, which further decreased the collapse resistance capacity of the SCCF system. After the removal of the exterior column, load was redistributed among the columns around the failed column and much more load was assigned to the adjacent exterior column. The flexural action and catenary action of the composite beams, as well as the tensile membrane action of the floor slabs worked together to resist collapse load at the large deformation stage.

Steel-concrete composite floor systems with different structural and loading configurations under a corner column removal scenario: Experimental tests

In this study, quasi-static tests were performed on three 3D steel–concrete composite floor systems under a column removal scenario with two variables, i.e., secondary beam connection type and pre-existing axial loads on columns. The work focused on the behavior of the three composite floor systems, including the load–deflection response, failure mode, load-resisting mechanism, e.g., flexure, catenary action and tensile membrane action (TMA), and load redistribution. It was found that secondary beam connection had a pronounced effect on the load–deflection response. Pre-existing axial loads on columns significantly influenced the load redistribution process and intensified the stresses in adjacent columns connected by the secondary beam to the removed column. For all the three specimens, a peripheral compressive ring with TMA was not observed in the composite slab due to a lack of rotational restraint from the perimeter beams and the main girder. However, at large deformation stage, when the composite slab deformed into an approximate hyperbolic-parabolic surface, the entire reinforcing mesh in the slab was in tension. It was observed that, at the early stage, the applied load was mainly resisted by flexure in the slab and the main composite girder and the secondary composite beam connecting to the removed column. But at large deformation stage, part of the applied load was resisted by flexure in the partially damaged slab and the main girder, and the intact secondary beam. Other load-carrying contributions came from catenary action in the main girder and TMA in the slab. In the end, most of the applied loads were redistributed to the columns adjacent to the removed column.

Simulation of steel–concrete composite floor system behavior at elevated temperatures via multi-hybrid metaheuristic framework

In this research, the principal purpose is investigating the performance of structural elements significantly degrades at elevated temperatures. Steel–concrete composite floor systems are one of the most relevant components in building construction in which fire-induced problems directly damage their performance. The purpose of this study is on employing analytical intelligence technique to predict two major structural characteristics of the steel–concrete composite floor system. Two intelligent methods, ELM-PSO and ELM-GWO, were used as a multi-combination AI method to predict the shear and tensile response of these composite floor systems at high temperature. Accordingly, authenticated data on monotonic loading response of this steel–concrete composite floor system in different heat stages had been employed from different literatures. The results show that ELM-GWO technique presented the best prediction of split-tensile load, and the ELM-GWO provided the best estimation of slip value. By giving each prediction equations, the best equations were proposed. As a result, employing ELM-GWO, successfully presented reliable and decisive results and proved the proficiency of the techniques.

Cost Optimization of Steel-concrete Composite Floor Systems with Castellated Steel Beams

Performance of cost optimization program of composite steel deck-slabs (DS) and supporting castellated beams (CB) consisting of interior beams, edge beams and girders is proposed in this paper. The program applies the vibrating particle system (VPS) meta-heuristic algorithm, which imitates the free vibration of ideal one-story frame structures with viscous damping. The program is also furnished with an advanced cost function, which takes into account both material and fabrication costs of all parts of the floor system. The effect of four major cost reduction procedures and additional cost-saving techniques are studied on the cost function. Considering various DS profiles, altering the dimensions of hexagonal openings, different number of floor divisions and choosing costlier DSs except the optimal deck are the major cost reduction procedures. Inclusion of partial composite action for CBs, infilling certain openings of CBs and applying camber are the supplementary economizing techniques. To realize the economy of LRFD method, a meticulous design theory of composite CBs in adherence with LRFD principles of AISC 360-16 specifications is applied to the formulation of the strength constraints. Due to excessive deflections and due emphasis on vibration control of CBs, we implement accurate design procedures for the formulation of the serviceability constraints. Performance and superiority of the proposed optimization program is validated by studying three distinct real-size design examples taken from the literatures.

Collapse Simulations of Steel-Concrete Composite Floors under Column Loss Scenarios

Characterizing structural resiliency after severe damage to a few load-carrying members is challenging. Engineers use various computational approaches to assess the vulnerability of structures and to evaluate the parameters that affect their response. Few of these approaches are capable of predicting the actual peak load-carrying capacity a damaged structure can withstand before experiencing total collapse, and practically none of them have been verified against actual test results. In this paper, experimental data from large-scale tests on steel–concrete composite floor systems under different column loss scenarios were used to develop and to validate a high-fidelity numerical modeling approach capable of predicting the response of the tests up to total collapse. This approach incorporates geometric and material nonlinearity, explicit modeling of steel and concrete failure, and contact modeling using LS-DYNA version R10.2.0. Nearly all specimen components were modeled using brick elements, including the concrete slab, steel members, bolts, and other connecting elements. The corrugated metal decking was represented with shell elements, and beam elements represent the reinforcing steel and shear studs. The predicted response and ultimate load–carrying capacity up to total collapse show good agreement with the results of the experimental tests. Validating the numerical models revealed the sensitivity of various modeling parameters and demonstrated the potential for inaccurate predictions of response when certain parameters were not correctly specified. The most important of these parameters are described in this manuscript. Lessons learned from the current study are helpful for understanding the mechanisms that have the greatest impact on collapse of composite floor systems, and these lessons can be used to gain insight on the collapse potential of other structures with different geometries or configurations.

Full-Scale Test of a Steel–Concrete Composite Floor System with Moment-Resisting Connections under a Middle-Edge Column Removal Scenario

AbstractTo investigate the load-resisting mechanisms and responses of typical steel–concrete composite frames under the progressive collapse scenario, a 2×1 bay full-scale steel–concrete composite ...

Numerical investigation on progressive collapse resistance of steel-concrete composite floor systems

Steel-concrete composite floor systems are commonly used in steel buildings. Stability under gravity and lateral loading depends on these systems. To better understand the design parameters that govern the progressive collapse behaviour of steel-concrete composite floor systems, high-resolution finite-element analyses (FEA) is conducted. Steel fracture and concrete damage are explicitly considered in the finite-element model (FEM). The model is validated using full-scale test data including comparison of the measured response and failure modes. The validated model is used to conduct a parametric study to investigate untested parameters including (i) concrete strength, (ii) horizontal constraint, (iii) steel deck thickness, (iv) reinforcement ratio in the composite slab, and (v) the number of the shear studs. The simulation results are used to determine the optimum design to increase progressive collapse resistance. Specifically, it is found that increasing the continuity and the horizontal constraint of the steel deck, the steel deck thickness, and number of shear studs increase this resistance. Considering the steel consumption and the common practice in the construction, improving the continuity and the horizontal constraint of the steel deck are the best choices to improve the collapse resistance.

An optimisation strategy for the (in- and out-of-plane) resistance of steel beams in demountable composite floor systems

Demountable and reusable composite floor systems enable the decoupling between the use of construction materials and economic activity, and hereby contribute to the sustainability of the built environment. Efficient material use through optimised cross-section design reduces construction material demand. Demountable steel-concrete composite floor systems are perceived as competitive when consisting of steel beams and large prefabricated concrete floor elements, with composite interaction achieved by demountable shear connectors. Compared to traditional monolithic floor systems, the demountable composite floor systems have an increased sensitivity to lateral-torsional buckling during execution, mostly because of unsymmetrical loading and the absence of rotational constraints in the execution phase. This increased sensitivity implies that the cross-section of the steel beam should not only be designed based on the required in-plane resistance, but should also maximise the out-of-plane resistance. The Energy method and Rayleigh-Ritz methods are combined to develop a prediction model for the critical bending moment of monosymmetrical web-tapered steel beams. The key cross-sectional dimensions and parameters that affect the in-plane and out-of-plane resistance are identified. An overarching strategy for the concurrent optimisation of the in-plane and out-of-plane resistance of monosymmetrical cross-sections is presented without compromising on material efficiency. The beneficial effects of the proposed optimisation strategy are quantified through a case study example.

Requirements for oversized holes for reusable steel-concrete composite floor systems

The design of sustainable structures is increasingly gaining attention in the construction sector as a societal and technological challenge. Demountability and reuse of structures contributes to the reduction of the environmental impact of the built environment. Welded headed studs used in traditional steel-concrete composite floor systems need to be replaced by demountable shear connectors to enable the transition of the construction sector to a circular business model. The demountable shear connectors are embedded in large prefabricated concrete floor elements and connected to steel beams by bolts. The holes in the beam flange are oversized to account for geometrical and dimensional deviations of all members and to facilitate rapid execution and easy demounting. The goal of this paper is to present a methodology that quantifies the required nominal hole clearance for reusable composite floor systems. Statistical characteristics of dimensional and geometrical deviations serve as input for Monte-Carlo simulations. The aggregated results of the Monte Carlo simulations are used to determine the required nominal hole clearance for a specified probability of successful installation of the demountable shear connectors. The proposed methodology is applied to the composite floor system of a demountable and reusable car park building. The contradicting requirement of oversized holes and composite interaction is solved by injecting the hole clearance with a (steel-reinforced) epoxy resin. The bearing resistance of the (steel-reinforced) epoxy resin is addressed based on preliminary results of creep experiments on resin-injected bolted connections.

Progressive collapse simulation of the steel-concrete composite floor system considering ductile fracture of steel

The prediction of the structural behavior under the progressive collapse scenario has received growing attentions in recent years. The failure of the bolted shear tab connection is usually dominated by the shear fracture. However, few researchers have considered the effect of the shear fracture in the progressive collapse simulation. This research develops a practical modeling routine to upscale the material shear fracture model in the collapse simulation of a large-scale floor system. The calibration and validation of the material shear fracture model employ five types of plate coupon specimens with significantly different stress triaxiality and Lode angle parameters. Via optimizing the coupon test data, this study determines the 3-D fracture locus of three fracture models, which are subsequently used to predict the fracture of a coupon specimen in the tension and shear conditions. Among the three fracture models, the Bai model has demonstrated good accuracy for a wide range of stress triaxiality and Lode angle parameters, while the applicability of the other two fracture models are confined to the stress triaxiality and Lode angle parameters, from which they are calibrated. These fracture models are also used to simulate the fracture of a girder-to-column connection under a center column removal scenario, which indicates the fracture in both the girder flange and girder web depends highly on the Lode angle. Prior to analyzing the full-scale composite floor system, the numerical study calibrates the fracture strain in the macro shell elements used to build the girder-to-column connection model, based on the fracture locus determined from the coupon tests. The fracture strain based shell element model is then used in the steel-concrete composite floor simulation, and demonstrates a good prediction of the structural resistance curve and the failure mode compared to the experimental results.