Steel-concrete Composite Floor Research Articles

Vibration Serviceability and Environmental Impact of Steel-Concrete Composite Floors Featuring Openings and Partitions

Vibration Serviceability and Environmental Impact of Steel-Concrete Composite Floors Featuring Openings and Partitions

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.

Seismic Retrofit of Concrete Buildings Damaged by Corrosion: A Case Study in Southern Italy

A case study of a building in southern Italy, subjected to high degradation by corrosion and waiting to be assessed for retrofit interventions, is presented. The owner required modifications to the building configuration, including a new layout of the floors and retrofitting for a high level of seismic load. A double strategy of an assessment and retrofit was carried out: dynamic linear and static non-linear analyses were performed, and the results were compared. Afterwards, a global strategy of mass and stiffness redistribution was implemented together with different retrofit interventions on the foundations, columns, and beams of the framed structure, such as reinforced concrete and steel jacketing, the application of FRP plates and fabrics, new steel elements, and steel–concrete composite floors. The results of the intervention are discussed and the implications of corrosion on the structures are explored. From the results obtained, it is possible to see how the use of different techniques for strengthening and passive seismic protection strategy can allow engineers to obtain the result of structural adaptation to earthquakes with low-cost interventions. The widespread adoption of steel jackets, coupled with the construction of floors using a steel–concrete composite structure, grants a good confinement of the beam–column r.c. joints, together with the overall strengthening of the existing structure. The adoption of CFRP wrapping at the lower edge of the beams implies a limited increase in thickness and the limited interventions of partial demolition from the existing structural members. A critical review of the steel jacketing aspects in terms of bending and shear strengthening is reported by considering this technique in the form of a steel exoskeleton containing the damaged concrete structure, by confining concrete elements, and by increasing the performance for both gravitational and seismic loads.

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.

Flexural behavior of modular steel channel–concrete composite floor systems with bolted connections

This paper presents an innovative modular steel channel–concrete composite floor system designed for rapid assembly. This system, compared to traditional steel–concrete composite floors, connects adjacent modules solely through the use of high-strength bolts. This design eliminates the need for on-site wet construction, thereby yielding superior economic benefits. To investigate the proposed system’s mechanical behavior, bending tests were conducted on four composite floors with various support conditions, the numbers of bolts, and the degrees of shear connection. The load–displacement responses, torsional behavior of the channel beams, interfacial slip, and strain development of the composite floor systems were analyzed. The test results show that the simply supported composite floor, without bolted connections, undergoes flexural failure. In contrast, the semi-continuous composite floors, with bolted connections, display punching shear-flexural failure. The pre-tension forces applied to the bolts can effectively mitigate the torsional deformation of the channels and module separation, ensuring that the system maintains excellent structural integrity, sufficient load-bearing capacity, and adequate ductility. The semi-continuous composite floors, when fitted with high-strength bolts, demonstrate an increase in ultimate load-bearing capacity by 13–15%. However, there is a corresponding decrease in ductility by 18–23% when compared to the simply supported composite floor without bolts. The use of perforated steel plates as shear connectors offers efficient shear resistance between the steel channels and concrete slabs, facilitating full composite action of the system throughout the loading process. The paper concludes with the development of a model that calculates the flexural strength and punching shear strength of the composite floors based on the yield-line theory.

Deflection prediction of assembly integral steel-concrete floor voided with steel mesh boxes

Steel-concrete assembled hollow core slabs have witnessed widespread adoption in recent years owing to their inherent advantages of reduced self-weight, enhanced rigidity, and superior integrity. Nonetheless, to achieve extended spans and expedite on-site construction, further optimization of the connections and fillers in these assembled slabs is imperative, along with fortifying the overall structural performance. Therefore, this study introduces a novel variant of assembly integral steel-concrete composite floor, incorporating voids filled with steel mesh boxes, which utilizes four prefabricated slabs featuring hidden transverse and longitudinal girders and a steel frame system. Concurrently, a large-scale experiment was conducted to explore its mechanical and deformation recovery performance. The detections indicate that this innovative structure exhibits excellent integrity, as the four prefabricated components transform from individual one-way slabs into a continuous floor, facilitating the efficient transmission of forces in multiple directions. A finite element model was established to provide ideas for the research of scholars in allied domains and a fundamental framework for the subsequent parametric analysis of the structure. Building upon the analog cross-beam method, the deflection of the novel structure is calculated. The resulting discrepancy between the calculated and experimental results is merely 1.87%, attesting to the practical applicability of this method. These findings provide a solid foundation, both experimentally and theoretically, for the future design and engineering application of composite slabs, fostering the advancement of sustainable construction practices.

Spectral modelling approach for crowd-rhythmic activities performed on steel-concrete composite floors

During the last decades, building floors have become sensitive to vibrations caused by human activities, especially when a group of individuals perform rhythmic activities in a coordinated manner. Resulting effects on floor occupants can range from a mere perception, can pass through discomfort and can even go so far to cause panic. The present paper proposes a spectral modelling approach for crowd-rhythmic activities applied on floor structures. The proposed model comprises a frequency domain model for a single person, combined with coordination factors to account for the lack of synchronization between individuals. The identification of this model was based on vibration experiments carried out on a floor specimen specifically designed for that purpose. Two particular types of rhythmic activity were investigated: jumping and skipping, and performed by up to 16 individuals, where realistic coordination stimulus was adopted. Using least-squares identification procedures, the single person load parameters were determined and predicted load models are in good agreement with their measured counterparts. Resulting parameters are dependent on the motion style of each investigated activity. Coordination factors are also derived from crowd forces and present a hyperbolic decrease by crowd size for jumping activities against an exponential decrease for skipping activities. Based on a closed-form expression using the established crowd model, a design-oriented method is proposed for a simplified evaluation of floor response due to crowd-rhythmic activities and verified against floor response measurements. Slight differences were found between measured and numerical responses due to the variabilities either encountered during experiments or resulting from the load identification process.

Resilient performance of steel connections with low yield point fuses considering the effect of RC floor slab

The beam-column connection of a steel frame equipped with replaceable low yield point steel cover plates (SF-LYCP) was proposed to address the significant repair challenge and financial losses caused by beam-column connection brittle failure after an earthquake. According to an experimental study, the SF-LYCP exhibited outstanding bearing capacity, ductility, energy dissipation, and post-earthquake rapid recovery performance. To explore the effect of the reinforced concrete (RC) floor slab on the mechanical behavior of SF-LYCP in a natural working environment, the finite element method of steel beam-column connection with low yield point (LYP) steel cover plates considering the effect of the RC floor slab (SF-LYCP-RCslab) was developed and analyzed by ABAQUS. The results demonstrated that the proposed finite method was able to accurately predict the behavior of SF-LYCP-RCslab. The load capacity, initial stiffness, and energy dissipation capacity of the SF-LYCP-RCslab were increased in comparison to the SF-LYCP. The LYP cover plates in the SF-LYCP-RCslab still played the desirable role of structural fuses. However, the concrete of the RC floor slab had severe damage and prevented the quick replacement of repairable LYP cover plates. Based on these findings, four improved strategies for the SF-LYCP-RCslab were proposed to reduce concrete damage and increase the replacement convenience of damaged elements. Comprehensively considering the bearing capacity, ductility, energy dissipation, structural fuse function, concrete damage, and post-earthquake rapid recovery performance, the improved strategy, which adopted a profiled steel–concrete composite floor slab with a gap, was recommended in steel frame beam-column connection design.

Shear resistance of welded studs in deck slab ribs transverse to beams

Accurate and reliable predictions of the shear resistance of welded headed studs in deck slab ribs transverse to supporting beams are essential for achieving safe and economical designs of steel–concrete composite floors. This paper presents the development of a new empirical design model for computing the stud resistance, based on machine learning methods combined with regression models, and its calibration via reliability analyses according to the Eurocodes and US design practice. As an alternative to using the new equations directly, reduction factors have also been developed from the proposed model, which can be applied to three existing resistance models for studs in solid slabs. Comparisons of the proposed model with seven existing models indicate that the former outperformed the latter. At the same time, the proposed model produces higher shear resistances while satisfying the reliability requirements for many combinations of parameters, especially for lower concrete strengths common in composite floors, thicker decks, and through-hole stud welding. It was also found that the proposed model is insensitive to the following parameters considered important by the existing models: the concrete elastic modulus, the normal force on the slab face (ranging from 0 to 20% of the longitudinal shear force), stud welding type (through-deck or holes), location of slab reinforcement, and deck yield strength. The proposed model produces shear stud predictions that can be confidently used in design whilst providing considerably higher resistances for certain parameter combinations than those computed with the existing models, including those adopted by Eurocode 4 and AISC 360.

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.

Structural Optimization of Lightweight Composite Floors with Integrated Constrained Layer Damping for Vibration Control

Due to current architectural trends, contemporary public buildings are becoming open-plan spaces with much less weight and damping. Consequently, Vibration Serviceability Limit State (VSLS) due to human-induced vibrations has become an increasing concern for structural engineers, especially when designing offices, hospitals, or gymnasiums. When dealing with resonant vibrations, a slight increase in the floor-damping enables decreasing considerably the vibration level. The damping strategy studied in this work is usually known in the literature as Constrained Layer Damping (CLD) and consists of a viscoelastic layer constrained between the concrete slab and the steel beam of a lightweight composite floor. In this paper, a complete structural checking methodology has been developed for analyzing all the limit states that determine the final sizing of a steel–concrete composite floor treated with CLD, including a detailed analysis of the VSLS. The methodology has been used for setting a structural optimization problem for floors with and without CLD treatments. Thus, it has been demonstrated that the integration of CLD treatments at the design stage of the building allows the development of lighter floor structures with a smaller embodied carbon (EC) footprint, especially for long-span schemes with restrictive vibration limitations.

Experimental and numerical investigation of the prefabricated steel–concrete open-web composite floor with embedded chords

To reduce the height and improve the installation efficiency of novel prefabricated steel-concrete open-web composite floor (SOF), a developed SOF was proposed. A full-scale (9.0 m × 9.0 m) laboratory test and detailed parametric finite element (FE) analysis were conducted to explore the load-bearing capacity, typical failure modes, load-displacement relationship, and strain variations at key locations of the structure. The experimental findings indicated that the concrete slab and upper chord exhibited good composite behavior, and no interfacial failure was observed between the concrete slab and the T-section. The joint diaphragm welds failed in tension due to insufficient capacity of the bottom chords, while web members continued to transfer axial tension, resulting in local tearing failures outside the plane. Further finite element analysis illustrated the damage evolution of the concrete slab and steel grids. Moreover, the mechanical properties of the structure were found to be relatively insensitive to the changes in geometric parameters across the different locations. The conclusions drawn from this study can be utilized as reference for the design and analysis of spatial composite slab structures.

Identification of a load model for crowd-rhythmic activities based on acceleration measurements of a building floor

The floors of modern buildings are prone to excessive vibrations induced by human actions, especially when a group of people perform rhythmic activities in a coordinated manner. A reliable model for this load case, taking into account the experimentally observed group effect, is thus essential for the serviceability assessment of such structures. In this paper, a frequency-domain load model for either a single person or multiple individuals was established for two rhythmic activities. The model parameters were determined by an indirect identification method from acceleration responses. An extensive experimental test campaign was conducted on a steel–concrete composite floor in order to provide input data for identification, including experimental modal analysis and human-induced vibration tests for up to 32 individuals. The load parameters were first determined for the single-person load model. Root Mean Square (RMS) forces were then calculated from the identified load models, and corresponding coordination factors as a function of crowd size are suggested. A decreasing exponential was obtained for up to 8 persons for skipping and 12 persons for jumping, followed by a constant plateau for larger groups. The proposed models involve a global coordination factor to be used in conjunction with the identified model corresponding to skipping and jumping activities. A comparison of the proposed model and three existing coordination factor models against experimentally identified forces was performed. The comparison revealed the accuracy of the suggested models with respect to experimentally identified forces, whereas differences to existing factors were found especially for jumping.

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.

SIMPLIFIED METHOD FOR PREDICTION OF VIBRATION BEHAVIOR OF STEEL-CONCRETE COMPOSITE FLOOR SUBJECTED TO GENERAL LOADING

Vibration serviceability problems have often been encountered in steel-concrete composite floors due to their long span and lightweight nature and have low damping depending on the occupancy. These are being used for various applications and hence are being subjected to different dynamic loads such as those due to human excitations and mechanical vibrations. Thus, it becomes necessary to predict the vibration behaviour at the design stage itself to avoid problematic floors. Previous researchers have extensively studied and presented simplified equations to understand the behaviour of floors subjected to human excitations such as walking, jumping, dancing, etc., but these equations are based on the beam mode of vibration. This paper presents a method that captures the behaviour of the floor alone subjected to a certain frequency and a general dynamic load. A novel displacement-controlled test to predict natural frequency was conducted in which the floor was subjected to vibration with a certain displacement over a range of forcing frequencies away from the natural frequency and the results conclude that the method shows good agreement with the traditional heel drop test and can be used for the purpose.

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

Parametric finite element study of novel corrugated steel deck for two-way action in steel-concrete composite floors

Composite construction using steel and concrete is a widely adopted flooring construction technique. Past literature has reported ample research in the development of composite one-way slabs. However, there is a lack of understanding of two-way action in these composite slabs. It has prevented the applicability of two-way steel-concrete composite slabs in floor construction. The performance of a novel deck composed of corrugated hat sections placed orthogonally at equal spacing on a corrugated base sheet has been investigated for achieving two-way action in steel-concrete composite slab construction. Non-linear finite element (FE) models were developed and researched for feasibility in two-way action using the commercial FE package ABAQUS. The decks were analyzed in the construction stage, that is, in the absence of concrete, to isolate the properties of the new steel deck. Various parameters such as depth and spacing of hat section, angle of hat section webs and aspect ratio of the decks were investigated to establish a suitable configuration for two-way action. The effect of the parameters on the load-deflection relationship and distribution of load in two directions were studied to optimize the two-way action. Decks were also analyzed for one-way action to benchmark the change in behavior of the corresponding two-way decks. Obtained numerical results showed that the proposed corrugated deck is efficient in two-way action and could be adopted in two-way steel-concrete composite slabs. The distribution of loads in both directions improved with a decrease in hat-section spacing but increased aspect ratio and depth.

Methods for Life Extension of Multi-Storey Car Park Buildings

Multi-storey car park buildings with steel–concrete composite floor structures are widespread in construction due to the distinct benefits of the implemented structural system. Although there are various possibilities for accomplishing composite action between a steel beam and a concrete slab, some solutions, such as friction-grip bolts commonly applied in the 1970s, did not show good durability. An example is the multi-storey car park building “Obilićev venac” in Belgrade. This case study presents two methods for life extension of the car park building structure. Both approaches focus on applying welded headed studs with the primary intention of providing a durable shear connection. While the first method has been applied during the structure’s reconstruction, the second method is proposed as a novel solution for implementation in steel–concrete composite floors. The application of the proposed connection is discussed and the results of the experimental and numerical research conducted are presented.

Experimental investigation on flexural behavior of steel-concrete composite floor slabs with distributed fiber optic sensors

This research investigates the flexural behavior of steel-concrete composite floor slabs with distributed fiber optic sensors based on pulse pre-pump Brillouin optical time domain analysis. The distributed sensors were embedded in trapezoidal concrete slabs and provided in-situ real-time monitoring of initiation and evolution of cracks in the profiled slabs of four composite floor slabs. This paper proposes a sensor deployment method for real construction of civil engineering structures and evaluates the effects of headed studs and concrete casting on the flexural behavior of composite floor slabs and the performance of distributed sensors. The composite floor slabs failed with concrete cracks, accompanied by yielding in the steel beams and slippage between concrete and steel. The distributed sensors captured complex crack patterns of the concrete slabs in the evolution of the damages in the composite floor slabs. The strengths and limitations of distributed sensors are discussed to promote applications and further development.