Composite Construction in Steel and Concrete VII

Over 25 years have gone by since the first Composite Construction in Steel and Concrete Conference was organized in Henniker, New Hampshire (USA), and this seventh conference presents a great opportunity to assess the impact that this series of conferences has had on American composite construction codes. The intent of this paper is to provide a brief history of both modern composite member design provisions in the USA and how this conference series influenced their development. The latter include important direct impacts on the design provisions for shear studs, composite columns, and serviceability provisions, among others. Looking forward, the paper also gives some preliminary results on provisions for the determination of the equivalent stiffness of simply supported beams to be proposed for the 2016 edition of the AISC specification. It is written as a personal reflection and is not intended to represent the points of view of any of the organizations mentioned.

The urban development of the city of Lucerne required the replacement of the existing Langensand road bridge by one designed according to modern standards of urban mobility. The bridge’s shape is the result of a synthesis between function, construction method, structure, and the urban context (extremely dense environment and several complex constraints). The bridge crosses 79.7m with one single span girder over 11 railway lines. Its composite structure has an extreme slenderness of about L/37. The paper describes the advantages and problems of a steel-concrete composite construction especially in regard to its structural system, and the evolution during the construction phases, and to its slender and flexible structure. The paper will compare and highlight the theoretical approach (hypothesis and numerical models for static and dynamic actions) with the results of in situ tests for the two principal states of the structure: firstly, the half bridge and secondly, the final connected bridge.

This paper describes the welding procedure qualification of the multilayer “lamellar” flange for modern bridge construction made in the Czech Republic. The fine-grained structural steel was used for construction and welding qualification. Weldability of this steel grade is briefly mentioned. Technological and proposed welding processes including weld joint preparation are described. FCAW welding in the overhead position is carried out by the seamless flux cored wire and SAW welding using solid wire in the flat position is applied. All required tests on the multilayer weld joint including tensile test, bend test, hardness distribution, impact test, and macroscopic evaluation are investigated. All test results are in good agreement with EN ISO 15614-1 standard requirements. Based on the satisfactory results, the proposed welding procedure for the multilayer flange weld joint can be qualified.

For (low cycle) fatigue design of steel foundation piles of composite bridges with integral abutments, not only traffic loads but also temperature loads as well have to be considered. Regarding this temperature fatigue load case, no specific rules and recommendations are given in EN 1991-2 (Eurocode 1: Actions on structures—Part 2: Traffic loads on bridges). The current paper proposes a simplified temperature load spectrum, to be used for (low cycle) fatigue design of constructional steel members of composite bridges with integral abutments. Therefore, effective bridge temperature hydrographs (100 year period) are derived by means of FE-calculations for various locations based on actual weather data. They are converted into pile strain hydrographs, taking into consideration residual strains and plastic deformations. The calculations are verified by laboratory low cycle fatigue tests and monitoring results. Finally, a design temperature load spectrum is proposed, based on classified temperature variations.

This paper describes the squash load of concrete-filled tubular (CFT) section columns with or without local buckling based on the compression test results. Local buckling of non-compact and slender steel sections is accounted for in the limiting stress formula specified for the steel skin of CFT columns in a similar manner to the AISC specifications. Simple squash load formulae for CFT stub columns for the direct strength method have been proposed to account for post local buckling strength of slender steel skin and enhanced concrete compressive strength due to the confining effect by the steel skin. The squash loads predicted by the proposed strength formula were compared with available test results and those predicted by the AISC specifications and Eurocode4. The comparison confirmed that the squash load formula proposed could predict the squash load of CFT columns conservatively.

Available theoretical equations for the shear capacity of composite joints vary in their assumptions for the shear deformation mechanisms and give different equations for calculating its shear strength. This paper discusses previously proposed equations for joint shear capacity, and suggests recommendations for obtaining more accurate predictions. Finite element analyses of through diaphragm connections to CFT columns were carried out in ABAQUS. ABAQUS results and theoretical estimations of the shear capacities were then used to define the properties of a rotational spring in a joint element in OpenSEES representing the shear deformation behavior of the joint. The OpenSEES and ABAQUS results were validated with experimental results from the literature. The results show that: (1) the steel tube flanges and not diaphragms dominate the shear deformation of the joint; and (2) the global behavior of the connection is very sensitive to shear capacity of the joint in joint yielding case.

This paper describes the effect of composite slabs in increasing beam strength and its implications for design. It also discusses the “beam-growth” phenomena, which can detrimentally influence the performance of a frame with reinforced concrete or precast concrete beams, and its impact on steel beams with RC slabs. From the subassembly testing conducted the slab increased the beam strength by around 40%. However, the slab could not maintain strength at large drifts without degradation with transverse or longitudinal decking placed around the columns. This indicates that while transverse or longitudinal slabs should not be considered in design to size the beam, they should be considered in the beam overstrength calculations for the design of other members. Also, both rational considerations and experimental results indicate that beam growth effects tend to be small for composite steel beams because the steel beams are able to yield in both tension and compression.

This paper describes the methodology for post-processing experimental data related to the axial strength of slender full-scale concrete-filled tubes. Although utilizing a state-of-the-art testing system, the results obtained during testing needed to be corrected to account for the compliance, frictional forces, resolution and capacity limits of the testing system, as well as the initial imperfections of the specimens. A complex load protocol, aimed at determining the buckling load capacity of CFT columns, a set of points in the P-M interaction diagram of CFT beam-columns, and the torsional strength of CFT members, was used. This load protocol consisted of a set of load cases applied sequentially: (1) pure compression, (2) uniaxial and biaxial bending combined with different constant axial load levels, and (3) torsion with and without constant compression loading. Successful post-processing of the data required the application of different techniques to correct, filter and extrapolate the measured experimental response. In addition, these efforts required that behavior of the loading system be characterized through integration of data from different sensors and computational simulations using stiffness and displacements obtained directly from the test.

This paper introduces a new type of connections—reinforced concrete (RC) ring beam joints between concrete-filled steel tubes (CFSTs) column and RC beam. In this connection, the continuous load transferring in the frame beams are achieved by the transitional ring beam encircling the CFST column. Bidirectional cyclic loading tests on four interior column joint specimens were conducted to evaluate the seismic performance of this new connection system and the influence of the reinforcement on the joint behavior. Test results indicated the multi-directional nature of the force system in the ring beam. RC ring beam should be designed against the combination of multi-directional forces including axial load, bending, torsion, and shear due to the interaction of ring beam and CFST column under external load. The connections with reasonable design were observed to have good ductility and suitable for seismic resistant application.

In order to investigate the bending capacity of composite beams constructed with high strength steel (HSS) sections, a three-dimensional finite element model allowing for both material and geometric non-linearity is described and validated against previous experimental results. An extensive body of parametric studies incorporating selected steel grades and degrees of shear connection is further undertaken. The flexural strength of such composite beams are analysed, and the effects of the steel yield strength and cross-sectional residual stresses are elucidated. Based on a comparison with composite beams using conventional mild steel, it is found that the method of rigid plastic analysis that is normally utilised to design composite beams with mild steel sections somewhat overestimates the bending strength of composite beams with HSS. There is no significant difference in the strength of a composite beam when considering the cross-sectional residual stress. A reduction factor is proposed for the adaptation of rigid plastic analysis, from which the prediction of the bending strength of composite beams with HSS becomes more accurate. This research has the potential to promote the practical application of HSS in composite construction, which is more environmentally sustainable due to the better efficiency of material utilisation compared with composite beams with lower-strength mild steel.

Current design specifications for steel and composite structures generally assume elastic-plastic or rigid-plastic material behaviour, which means that the beneficial influence of strain hardening is neglected. This assumption may lead to overly conservative strength predictions particularly for stocky bare steel sections and composite beams subjected to sagging bending. The continuous strength method (CSM) is a deformation based design approach that allows for strain hardening in the design of metallic cross-sections. Although the method has been successfully applied to bare steel, stainless steel and aluminium alloy cross-sections, use of the CSM for steel-concrete composite structural components, which may considerably benefit from strain hardening, has not been extensively studied. Thus, the primary purpose of this study is to extend the application of the CSM to composite structures, with an emphasis on simply supported beams subjected to sagging bending.

A laboratory investigation to determine the long-term behaviour of timber-concrete composite (TCC) beams was started from August 2010 at the University of Technology, Sydney. The test was conducted on four six-meter-span TCC beams; this paper reports the results to-date for only two beams. The materials used are laminated veneer lumber (LVL) for the joists and 32 MPa concrete for the flanges. From the start of the test (August 2010), the specimens have been under sustained loads of (1.7kPa) whilst the environmental conditions have been cyclically alternated between normal and very humid conditions (typical cycle duration is six to eight weeks) and the temperature remains quasi constant (22 °C). During the test, the mid-span deflection, moisture content of the timber beams and relative humidity of the air are continuously monitored. The investigation is still continuing and this paper reports the results of the experimental investigation for the last two and half years.

The composite slim-floor beam (CoSFB) solution is based on the development of an innovative composite connection. This connection is achieved by arranging reinforcement bars through the web of the slim-floor beam, hardly adding to complexity in fabrication or costs. By this technology, an economic and efficient method to activate the full effective width of the concrete chord (EN1994-1-2) for slim-floor beams has been innovated. In order to structurally assess the system, push-out tests, shear beam and long beam tests with focus on structural, vibration and deformation behavior of the CoSFB have been performed. Their evaluations show an increase of the load bearing capacity by 100% and of the stiffness by 150%, compared to non-composite slim-floor beams. The shear connection provided sufficient resistance with a ductile load-deformation behavior. This paper presents the experimental results, their evaluation, and their comparison to existing design approaches of reinforcement bars as shear connectors.

This paper presents a long term experimental study to quantify changes in dynamic response due to a long term loading and varying temperature effects. The experimental study is set up for one year. Two types of blind bolt connectors were used as shear connection systems in steel-concrete composite beams alongside a welded shear stud system and a non composite beam. Two questions are answered; firstly, do composite steel-concrete composite beams experience a change in frequency and/or mode shape due to environmental factors. Secondly, for identical specimens, does the type of shear connection system used change the extent to which environmental factors affect the frequency of the specimens. The results indicated that the dynamic behaviour is affected by both the load and changes in environmental factors over the course of the year as expected. The extent of the effect is dependent on which type of shear connector is used.

Deltabeam is a hollow slim floor beam made from welded steel plates with regular web penetrations. Due to the long spanning capabilities of this product, the Deltabeam technology has recently been used in a prestigious shopping centre in the UK. As the floor would be subject to continuous walking activities the main contractor, Bovis Lend Lease, was concerned with occupant-induced vibrations. This paper presents the results from vibration tests conducted by the University of Sheffield, which can be compared directly with the requirements given in ISO 10137. Through extending the scope of the test results by numerical modelling and applying the design rules given in SCI P354, a methodology has been developed to estimate the vibration performance for this floor type and is presented.

The methods proposed by the design codes for single member design in fire situation assume that these members are isolated in their response. The real response of structural members such as beams is, however, more complex due to thermal expansion and the presence of restraints against this expansion by the surrounding structure. It is therefore imperative to study the response of structure at high temperature in a way which includes its interaction with its surroundings such as in a full-scale fire test and in numerical analysis. This paper focuses on the numerical investigation of steel beams, with a concrete slab and connected to concrete filled tubular (CFT) columns through reverse channel connections. The finite element software ABAQUS has been used in this study. The aim of the investigation is to study the behaviour of the composite steel-concrete beam exposed to increasing temperature in fire.

For the fast construction of bridges, it is necessary to design bridges as light and modular superstructures. For this purpose, a new composite bridge constructed by segmental method is suggested, which consists of concrete filled steel tubular girders and prefabricated concrete decks. This paper presents a study of the structural behavior of the proposed CFT truss girder at a continuous under negative bending moment. A numerical analysis is performed to verify the structural behaviors of CFT truss girder in continuous support. Based on the results of a numerical analysis, a model with a continuous composite member shape is fabricated and static tests are conducted.

Steel-concrete composite beams can often be subjected to combined bending and high axial forces. However, the moment-axial force interaction in composite beams is not covered by the current codes of practice. An experimental investigation comprising twenty-four full-scale tests was conducted recently in the University of Western Sydney, aiming to investigate the behaviour and ultimate strength of composite beams under bending and axial forces. Nonlinear finite element simulations and parametric studies complemented the tests. It was found that the moment capacity of a composite beam is reduced in most situations under simultaneous axial loading. Partial shear connection does not alter the shape of the interaction curve, but it affects the ductility of the beam and the amount of axial load transferred to the slab. Based on the experimental and numerical results, simplified design rules are proposed to account for the effect of axial loads on the bending capacity of composite beams.

The shear strength and the moment-shear interaction in steel-concrete composite beams was previously evaluated by the authors through an experimental program comprised of fourteen tests on simply-supported composite beams. In this paper, a nonlinear finite element model is developed to simulate the behavior of the experimental section. The model was assessed in terms of the ultimate strength and the failure modes of the composite beams under shear and bending and found to be accurate in capturing the nonlinear response of the specimens. The numerical model was then used to carry out an extensive parametric study on the various factors that influence the shear strength of a composite beam. These factors include the slab thickness, the slab width, and the reinforcement ratio. Based on the results of the numerical study, design models are proposed for the calculation of the shear strength and the shear-moment interaction in composite beams.

This paper contains a parametric study for the development of the nominal flexural strength of conventional composite girders and hybrid composite girders using HSB high-performance steels in positive bending region. The flexural strength and the ductility of a wide range of conventional or hybrid composite girders are calculated using moment-curvature analysis, and the plastic moment of each section is obtained using simple plastic theory. For developing new design equations, the obtained flexural strength and the ductility of conventional or hybrid composite girders are compared to the previous research work and the current AASHTO LRFD’s design equations. The comparison results show that there are considerable differences in flexural strength distribution between the conventional composite girders and the hybrid composite girders. It was also observed that in case of the hybrid composite girders, until considerably high ductility parameter, the flexural strength is not smaller than the plastic moment. Based on the results of parametric study, new design equations are proposed for predicting the nominal flexural strength of conventional or hybrid composite sections.

Floor vibration due to human activity has become increasingly recognized by structural engineers, architects, and building owners as an inherent issue in long-span steel framed floor systems. In the past, attention was primarily focused on strength and deflection serviceability limits. However, as designers seek to push the limits on structural spans, grid spacings and adopt light-weight, low damping structural steelwork floor systems, more detailed consideration is required of the design tools and processes available to analyze and predict the vibration performance of floor systems. Selection from published criteria of an “acceptable” vibration limit is sometimes possible depending upon the intended use of the space and the availability of manufacturers’ data for any vibration sensitive equipment. Building owners and user groups often have little understanding or quantitative “feel” for what performance the proposed “acceptable vibration limit” actually represents. The theoretical predication of vibration performance against actual measured performance can sometimes vary significantly. This can lead to dispute post-construction as to whether the floor has an “acceptable” level of vibration. Post construction remediation of a space that is deemed to be “too lively” is often difficult, therefore, it is important that the vibration design criteria proposed are discussed and agreed and the limits of theoretical predications of vibration performance are clearly understood by all parties at the outset. Beca Ltd (Beca) are currently in the process of designing two projects at the University of Auckland, utilizing long-span partial-composite cellular steel beams. Both buildings will utilize existing structural frame layouts and foundations. As the new structure is to be built on the existing foundations, there is a necessity to keep it as lightweight as possible. The question of vibration sensitivity has been raised as a potential issue as both buildings contain research laboratories. An in-depth investigation has been conducted into the factors affecting vibration performance in order to give the client and user groups confidence that footfall induced vibration will not be an issue with the proposed floor structure.

The Leadenhall Building will add a very distinctive shape to the London skyline. The external steel megaframe is one of the most visible parts of the building but the composite floors also include innovative features. The analysis for footfall vibration and the design of the floor beams for axial force used new approaches but the most significant innovation was the use of precast planks to span between the steel beams. The connection between the planks and the steel beams was developed partly in response to the specific challenges encountered on this project. Continuity between the planks for negative bending and in-plane shear was provided by the use of bars with threaded couplers and ducts cast into the planks. To transfer the shear between the slabs and the beams, a tab connection was used. A series of tests was carried out to establish the properties of the connection and validate the system. Results are presented in this paper.

This paper describes investigations into the structural behaviour of ferritic stainless steel floor decking in composite construction. Although commonly used in the automotive and industrial sectors, structural applications of ferritic stainless steels are rare owing to a relative lack of knowledge, performance data, and design guidance. These materials display considerably better atmospheric corrosion resistance than carbon steels, as well as having good ductility, formability and excellent impact resistance. As part of a wider investigation into the use of ferritic stainless steels in structural applications, an experimental study has been undertaken to assess the viability of using these materials for the profiled decking in composite floors. The shear connection behaviour between the steel beams and the composite slab is clearly critical and this is influenced by the through-deck welding process of the shear connectors. The practicality of this welding technique is assessed and described in this paper. Furthermore, the results of a series of push tests are presented. These enable the resistance of the shear connectors to be established and compared with the strengths specified in EN 1994-1-1 for composite slabs using galvanized steel decking.

About 10 years ago, the idea arose of developing a new flat slab type with integrated building services. The first idea concentrated on a pre-fabricated slab element with a sandwich cross section. The open space (hollow space) between the two outer shells of the sandwich is available for various installation devices. It was also necessary to provide appropriately large openings in the web members joining the two outer shells. In order to provide the necessary strength around the large openings, a steel plate was embedded within the concrete web element. Appropriate composite connecting means were additionally needed to provide bonding capacity to the respective outer shells of the sandwich. In order to satisfy these requirements for the bonding devices, two independent solution proposals were offered. The web members were additionally pre-stressed, in order to reduce the absolute values of the shear stresses. In order to optimize the bonding element, two variants were tested. Different projects were built with the new composite element.

This paper proposes a simplified slab model, which can be easily incorporated in the commercial software ABAQUS for collapse analysis of 3-D composite building frames. The proposed model avoids complex geometric modelling of metal deck profile and requires less computational time for analysing large building frame. Verification studies have been carried by comparing the results with established experimental and numerical data available from the literature. The proposed slab model was applied to a three dimensional 9-storey building frame and the results are compared with the model without the floor slabs. Numerical results show that incorporation of slabs in the model reduces the beam deflection by as much as 50%. As one of the failure criteria for the progressive collapse is related to limiting beam deflection, the present of slabs tends to reduce the beam deflection and enhance the robustness of the building against progressive collapse.

The issue of sustainability is becoming increasingly important in all industries. Above all, the construction industry is affected by a high use of materials and a large amount of waste. Therefore, a large contribution to sustainability can be already made by a specific choice of designs and materials in the design phase of buildings. Within the scope of the German FOSTA research project P881 “Sustainable office buildings in steel composite construction” recommendations and planning tools for slabs and columns in consideration of structural and technical as well as economic and ecological requirements will be created. In this paper, the requirement profiles of floor systems are given. After an introduction to the environmental and economic performance, the possibilities of an environmentally compliant design for structural components are discussed. This includes the optimisation of static, ecological, and economical aspects. Furthermore, concepts for the increase of resource efficiency are demonstrated.

Composite construction is a popular and effective method of construction, exploiting the strengths of both reinforced concrete and structural steel in building construction in a complementary fashion. Within paradigms related to minimisation of emissions and maximisation of product recycling, these composite systems are problematic on a number of fronts. Firstly, common and traditional composite systems utilise ordinary portland cement, which is known to be a very large contributor to atmospheric CO₂ emissions. Secondly, for typical construction practices for steel-concrete composite systems, casting of the concrete onto profiled steel decking and conventional reinforcement placing are undertaken on-site, which is time consuming and labour intensive, and which can increase the cost of construction. Thirdly, composite action between the steel beam and the concrete slab is usually achieved by using headed shear studs. The headed shear studs connect these two elements permanently, which leads to much waste at the end of the service life of the building when it is demolished. This paper models a sustainable semi-rigid beam-to-column composite blind bolted connection with deconstructable bolted shear connectors using ABAQUS finite element (FE) software. In this “green” system, precast geopolymer concrete (GPC) slabs are attached compositely to the steel beam via pretensioned bolted shear connectors and the composite beam is connected to GPC-filled square columns using blind bolts. Non-linear material properties and non-linear geometric effects are considered in the simulation of a connection in hogging bending. Based on the FE modelling, using pretensioned bolts as shear connectors with GPC can improve the behaviour of semi-rigid flush end plate composite joints in terms of ductility and load capacity. Moreover, the behaviour of the bolted shear connectors should be considered in composite joint design as being very different to headed stud connectors.

Experimental investigations on the behaviour of composite steel-concrete beam-to-column joints are presented. The undertaken subject is related to the design of multi-storey buildings that are not only subjected to common actions including persistent design situations, but that could also be exposed to accidental situations (such as explosion, fire, or impact) resulting in local damage to the structure. At this stage of the investigations, two separate experimental arrangements are considered, which allow the behaviour of joints under negative (hogging) and positive (sagging) bending moments to be modelled. The aim of the experimental tests is the observation of possible failure modes of the joints and a comparison of results expressed in terms of joint moment-rotation characteristics. Analysis of the joint properties for different load situations would ultimately allow for the formulation of recommendations for engineering practice.

The Eurocodes recognise robustness as a way to ensure the structural integrity of a building frame subjected to an unforeseen event and therefore to avoid a so-called “progressive failure” mode in extreme loading situations. However, few practical guidelines exist nowadays which would allow a designer to design a structure accordingly. Within the European RFCS ROBUSTFIRE project, the behaviour of steel and composite car parks subjected to localised fire leading to a column loss was investigated. Under such a scenario, the beam-to-column joints play a key role in the global structural response. Indeed, these joints, initially loaded in bending, may be subjected to elevated temperatures and to combined axial load “N” and bending moment “M”. In this paper, a methodology to predict the mechanical response of bolted composite beam-to-column joints at elevated temperatures under M-N is presented and validated through comparison to experimental tests conducted at the University of Coimbra.

Investigations on improving characteristics of concrete structures utilizing fibre reinforced concrete (FRC) have gained momentum in the last few decades. Using suitable fibres and additives in concrete to advance its performance is an important consideration in the construction industry. With regards to structural aspects of concrete, the important goal of this project is to improve the ductility of the concrete beam column joints, which helps eliminate or reduce the need for steel reinforcement. Fibres within the matrix, can bridge the cracks, which improves the performance of concrete matrix and results in a better stress bearing concrete material. This research project aims to investigative the effect of polypropylene (PP) and steel fibre volume percentage within the concrete on its mechanical properties. Concrete fresh properties as well as hardened properties have been tested and evaluated to work out the best fibre percentage to be added to concrete structure. From among the trial mix designs, five sets of FRC have been fully tested for the mechanical properties and also evaluated for the beam column concrete joint behaviour. Slump, mass per unit volume and air content have been tested to work out the fresh properties of concrete. 7 and 28-day compressive strength and also indirect tensile tests have been performed on the hardened concrete the results of which are presented in this paper. By using 0.5% by volume fraction of 30mm steel fibre, the indirect tensile strength of concrete has increased by 21%; however, when 1% of steel fibre has been utilized, about 45% increase has been observed. Furthermore, a sample of the joint test conducted will be presented in this work to illustrate the finite goal of this project.

The demand for economic and eco-efficient solutions in construction industry is particularly enforcing efficient design and construction methods. The design of composite construction according to the plastic hinge theory in combination with semi-rigid joints provides one contemporary promising answer to these demands. This combination enables to mobilize almost all cross section and system reserves. However, the capability for redistribution of the bending moment from internal support to mid-span, to activate these system reserves, requires sufficient rotation capacity of the composite beam and, especially, the connections. This paper presents design guidance on plastic and robust design of composite beams with semi-rigid composite connections with special focus on the influence of the reinforcement (ratio, diameter and type). With the provision of an engineering logic, new opportunities to design elegant and slender structures are given to engineers in a simple way.

This paper introduces a semi-rigid joint model to capture the composite beam-to-column joint behaviour so that the influence of joints on the building frame can be assessed precisely. The beam-to-column joint is modelled using a 6-degree of freedom non-linear connector. Depending on the joint type (e.g., simple, rigid or semi-rigid), connector load deformation behaviour can be represented by axial force-displacement relationship and moment-rotation relationship. This will avoid detailed finite element modelling of joint components to improve the computational efficiency of analysing large three-dimensional (3D) building frame. Analysis of 3D frame shows that the use of semi-rigid joint model predicts less beam deflection and higher load carrying capacity compared to pin-joint model. The incorporation of semi-rigid joint model in 3D frame analysis tends to produce more realistic estimate of frame behaviour compare to model using pin or rigid joints.

Concrete filled tubular structures have advantages to overcome stability of thin plates and to increase stiffness. A hybrid bridge combining common steel box girders and truss girders was suggested to increase the span length of steel-concrete composite bridges. In negative moment regions, a truss girder has lower chords of concrete filled rectangular steel box section to increase flexural stiffness. A bridge model with span length of 30m was fabricated and static tests were performed to assess the effect of composite chords on the flexural behavior of the girder. Depth of the girder varies from 2.0 m to 3.0 m. Significant reduction of stresses in lower steel chord was observed and measured deflections showed a good agreement with calculated values considering the contribution of infilled concrete. Cracking and crack width of the upper concrete slab were observed and indirect crack control by longitudinal reinforcing bars can be used for the design.

Composite structures using steel joists mechanically connected to concrete slabs serving as the flooring and decking systems are commonly used in buildings and bridges, respectively. The use of the state-of-art precast geopolymer concrete slabs coupled with innovative deconstructable pretensioned bolted shear connectors under service loads in a life-cycle composite beam design can reduce CO₂ emissions, thereby enhancing the sustainability in and recyclability of the construction industry. Most previous research has been conducted on composite beams with welded shear studs that cannot be deconstructed easily. A number of push tests are reported in the current study to establish the interface strength and stiffness characteristics of the bolted shear connectors. The application of the push test data in predicting complex full-scale composite beam behaviour with three distinctive regions that are delineated by the shear flow force at the interface, by the coefficient of friction at the interface and bolt pretension, and by the size of the clearance hole relative to the diameter of the bolt is explained. An initial theoretical investigation based on a simple mechanics-based “full-zero-full” shear interaction mechanism is presented and discussed.

The object of the present investigation is to study the effect of polyvinyl alcohol (PVA) fibres on dynamic properties of concrete containing fly ash as partial replacement for portland cement. Specimens of different concrete types, with variations in the length of fibers and proportioning, have been investigated to assess the performance of uncoated PVA fibre of two geometric lengths (6 and 12 mm) in concrete. Based on total concrete volume, 2 fibre fractions of 0.25 and 0.5%, were evaluated for their effect on damping ratio, fundamental frequency and dynamic modulus of elasticity of PVA fibre reinforced concretes (FRCs). From the results, it can be stated that although PVA fibre addition in low volume fractions used in this study significantly enhance the mechanical properties of FRC, it has no considerable effect on concrete material and RC beams dynamic characteristics.

This paper presents the fire resistance test results of 6 concrete filled stainless steel tubular (CFSST) columns. The influence of various parameters, including the cross-section type (circular and square), the load ratio (0.3, 0.45) and the presence of steel reinforcement (plain and reinforced concrete), were investigated. To capture the initial imperfections of the CFSST columns, a photogrammetry method was employed for the measurement prior to the fire testing. Fire tests were conducted on the CFSST columns under axial compression. The failure mode, temperature distribution, deformation, and fire resistance of the CFSST columns are presented and discussed.

In this study, static loading tests were conducted on concrete encased steel (CES) shear walls. One experimental variable was the construction method, using precast and integral construction specimens. Another variable was the shear span ratio, in which specimens were designed to fail either in shear or in flexure. This paper describes the test and investigates the failure mode, ultimate strength, and restoring force characteristics. Results showed that the maximum shear force resistances of precast walls were smaller than that of integral construction walls. Precast shear walls showed slip at the boundary of the wall panel and CES frame at a small level of drift angle, implying that the slip deformation affects shear strength resistance of precast shear walls. Further, it was found that the flexural strength CES shear walls can be evaluated using a method based on the Architectural Institute of Japan (AIJ) design standard for steel reinforced concrete (SRC) structures.

Coupled core wall systems are being used in seismically active areas worldwide as an effective type of structural system for resisting earthquake demands. At the University of Cincinnati, the design evolution of an innovative type of steel coupling beam was investigated that provides a significant advantage for structures utilizing linked concrete walls. The concept of post-event reparability can be realized through the use of a steel coupling beam in which a weak-link, or ‘fuse’ section is induced at the center of the clear span of the beam. During extreme seismic events on a fused coupled core wall system, all inelastic response is focused onto the weak link while the elastic integrity of the surrounding embedded beams and walls is ensured by careful detailing. A code-compliant design procedure has been established that preserves the intended performance. Results and conclusions from the analytical modeling of a 20-story structure indicate that steel fuse coupling beams perform favorably in a seismic event. Data from experimental tests demonstrate the adequacy of the design procedure and show the performance under cyclic load demands.

This paper presents the results of a fire testing program of four concrete filled circular hollow section columns with solid steel core. The structural fire behaviour is analysed by means of the recorded deformation–time as well as temperature–time course. Thereby it is shown, that after the temperature induced failure of the tube, the load is redistributed to the core. Depending on the pre-loading level, these columns can subsequently sustain the load with a bounded rate of deflection, until runaway failure occurs when the temperature induced stiffness degradation of the core sets in. A three-dimensional FEM model is validated with one of the fire tests and the influence of the support conditions, the eccentricity of the load and the input data of the constitutive model of the steel core are studied.

Hybrid precast twinwall concrete units, mainly used in basements, core and crosswall construction, are now being adopted in water retaining tank structures. Their use offers many advantages compared with conventional in-situ concrete alternatives. However, the design could be optimised further via a deeper understanding of the unique load transfer mechanisms involved. In the tank application, twinwall units, which consist of two precast concrete biscuits connected by steel lattices and an in situ concrete core, are subject to bending. Uncertainties about the degree of composite action between the precast biscuits and hence flexural performance of the units necessitated laboratory tests to investigate the interface shear resistance. Testing was also required to assess both the leakage performance and buildability of a variety of joint details. This paper describes some aspects of this novel approach to the design/construction of tank structures as well as selected results from some of the tests that were carried out.

Steel-concrete composite frames have been shown to be a sensible option for use as the primary seismic force resisting system of building structures. However, there remains little data to justify the structural system performance factors (i.e., R, C_d, and Ω_o) that characterize the overstrength and ductility of these systems, which are a vital component of successful design in the United States. Based on a suite of new finite element formulations, this work investigates the behavior of composite moment and braced frames under seismic loading and develops rational system performance factors. A set of archetype frames, selected to be representative of the range of frames seen in practice, were designed according to current design specifications. Nonlinear static pushover and transient dynamic analyses were performed on the frames to generate the statistical data on the seismic response from which the performance factors are quantified. The results from this investigation enable a better understanding of the variability in collapse performance of composite frame systems and will facilitate more effective designs of these systems.

Assessment of damage costs due to an earthquake is an important issue for the insurance industry, yet it currently lacks real damage data for realistic pricing of individual risks. Sophisticated numerical tools, which are widely used to assess structural behavior in great detail (like FEM), may be used with confidence in modeling damage and therefore, they may be suitable in seismic risk assessment for insurance purposes. To produce a virtual damage database, the “Simulated Building Portfolio”-Tool (SBP-Tool) was developed at the University of Kassel in cooperation with the Munich Re. This paper presents the first virtual portfolio for steel-concrete composite frame structures. The SBP-Tool uses beam elements for the composite columns and steel girders, and shell elements for the concrete slabs. Shear springs are automatically created to model the composite action between concrete slabs and steel beams. Rotational springs model the semi-rigid beam-column connections.

This paper describes part of an on-going research project within the Centre for Infrastructure Engineering and Safety at UNSW on an investigation of the strength behaviour of SFRC composite slabs having deep steel trapezoidal decking. It describes three groups of short-term load tests on single-span SFRC composite slabs, the test methodology being adopted from Eurocode 4 for the determination of the values of the parameters m and k. The aim of the tests was to study the effect of the presence of steel fibres to the longitudinal shear-bond strength at the interface between the steel profiled sheet and the SFRC concrete slab. The load-deflection responses and the end slips were closely monitored in order to gain a clear insight into the shear-bond behaviour of the test specimens. The concrete properties, including its compressive strength, tensile strength, modulus of elasticity and fracture energy were measured on companion specimens for every test group. The results were used to calculate the longitudinal shear bond strength by using partial interaction theory to provide benchmark experimental results.

Over the last decades, composite structures made of steel and concrete have been developed in order to allow for the economic and competitive construction of buildings and bridges. A main challenge of such structures is the design of the connection between the concrete and steel sections because of high requirements for the load-bearing capacity and ductility. Currently, headed shear studs are the only shear connectors regulated in Eurocode 4. In addition to common vertical shear studs, other shear connectors have been tested over the past decades. Concrete dowels, which are novel and versatile shear connectors, have been most extensively investigated. For the application in slender concrete slabs, for example in sandwich constructions, vertical headed studs and concrete dowels are not suitable, as they are limited by their height. In these constructions, it is possible to apply horizontally positioned concrete dowels. This paper deals with the experimental results of horizontally positioned concrete dowels in push-out tests.

Composite dowels are known as powerful shear connectors in steel-concrete-composite girders. More and more they are used in practice especially for prefabricated composite bridges. Advantages over headed studs are in particular the increased strength, the sufficient deformation capacity even in high strength concrete and the simple application in steel sections without upper flange. However, missing provisions in standards for composite dowels with the economic clothoid and puzzle shape have led to retentions of clients and delays in the approval process. Hence, the aim of the recently finished German research project P804 founded by FOSTA-Research Association for Steel Application was to solve open questions concerning these innovative shear connectors and to prepare a general technical approval available for any design office and construction company. In this paper design concepts for ultimate limit state and fatigue limit state, structural design principles and instructions for production and construction are presented and background information are given.

A composite beam is an effective building technique. The shear resistance of such elements is realised by using mechanical components, for example shear studs, which are leading to high local strains in the concrete slab. These local strains can cause high local stress in the steel. The application of adhesive technology avoids these high local stress peaks and enables new designs with the use of novel materials. The durability of adhesive connection is of high importance under climatic and thermal influence. Lack of knowledge of the long-term behavior of bonded joints, especially on long-lasting climatic effects is responsible for the lack of applications in building structures. The project aims to investigate the application of adhesive bonding as an alternative or supplement to mechanical joints in composite structures. The research objective is to obtain knowledge of the structural behavior of shear connection between steel and concrete in dependence of the inherent stress condition and material behavior in the adhesive joint. First, results of small specimen are presented.

The construction industry in Europe consumes over 70,000 million tonnes of a wide range of materials each year, and generates over 250 million tonnes of constructional waste. Much of the environmental impact of buildings is associated with consumption of resources and generation of waste, therefore reducing waste in construction is becoming a top priority for all the European governments. Composite structures formed by connecting the concrete slabs to the supporting steel beams have been widely used for many years throughout the world, this cost-effective arrangement for floor system in multi-storey steel frame building structures is responsible for a considerable increase in the load-bearing capacity and stiffness of the steel beams, which has resulted in significant savings in steel weight and construction cost. However, shear connectors are welded through the steel decking and cast into the concrete; this made deconstruction and reuse of the steel components almost impossible. A demountable shear connector is developed to assess its potential and suitability in term of replacing the welded through headed shear studs. Test results shown that these shear connectors can be easily demounted both at working and ultimate load and have a similar capacity to the traditional welded shear connectors. In addition, the new demountable shear connectors process high ductility in comparison with the welded shear connectors and have similar behaviour to the traditional welded headed stud shear connectors. A fnite element is developed to carry out parametric study for this form of shear connector.

This paper deals with of a new type of steel-concrete connection for composite beams. The connection is an alternative solution for steel-concrete composite bridges suitable for prefabrication and fast erection. The composite action of the beam is established through an innovative shear connection using adhesion, interlocking, and friction. The resistance of the connection to longitudinal shear is based on the development of shear stresses in the confined interfaces that form the connection. The interfaces include a steel-cement grout interface and a rough concrete-cement grout interface. Confinement is provided by the reinforced concrete slab that encloses the connection. This study applies such a connection to composite bridges and investigates resistance to cyclic loadings using experimental tests. The paper presents the analysis of the test results and a design method to predict the connection fatigue resistance.

This paper presents a novel experimental and numerical analysis of composite steel-concrete beams at elevated temperatures utilising carbon nanotube. Push tests were conducted as a part of the experimental study to determine the strength of the headed stud shear connectors in both normal concrete and carbon nanotube concrete. The specimens were tested under ambient temperature, 200°C, 400°C, and 600°C, respectively. Results from the experimental study illustrated the reduction of ultimate load and stiffness as temperatures increased. The numerical analysis was in good agreement with the experimental study results. Even though carbon nanotube had no effect on the ultimate load, however, the carbon nanotube reduced concrete spalling and cracking when compared to normal concrete. The carbon nanotube was observed to take effect at temperatures greater than 400°C. As a conclusion, the carbon nanotube concrete material would be an effective choice for reducing concrete spalling and cracking when exposed to elevated temperatures.

The stiffness, strength, and arrangement of the shear connection play a crucial role in the design of timber-concrete composite (TCC). This paper reviews the available analytical models for prediction of the stiffness of TCC shear connections. The methodology of different analytical models for stiffness of the mechanical fastener TCC connection is discussed and the accuracy of these models is examined based on push out test results for shear connectors. The simplified stiffness models underestimated the experimental data of normal wood screw with an error ranging approximately 10–40%, whereas the models based on Winkler’s theory were inaccurate and calculated a much lower stiffness compared to that of experimental test with an error of approximately 60%. The reasons attributed to inaccuracy of the stiffness models are described. This paper recommends further investigation on the prediction of foundation moduli of timber and concrete as the main input parameters of the models based on the Winkler’s theory.

Recent research studies carried out on the condition of the existing infrastructure in Australia have revealed that the percentage of structures reaching the end of their useful life has increased. These structures need alternative structural solutions to extend their useful life to reduce the costs on ‘new builds’, which are required to replace them. Therefore, methods of strengthening of composite steel-concrete structures have become increasingly important. The flexural behavior of composite steel-concrete beams using blind-bolts was tested using full-scale beam specimens previously. The test results revealed that the ability of these new blind bolts to achieve composite action in composite beams was comparable with that of welded stud shear connectors. In addition, the behavior of the full-scale beam specimen during the flexural test was simulated using three-dimensional non-linear finite element (FE) models developed using ABAQUS. The FE models were validated using the load-deflection curves obtained from the experiment. This paper presents the FE results of composite beam models containing different shear connectors.

Prefabricated steel and concrete composite decks are an interesting option to improve competitiveness and sustainability of the composite structures. Longitudinal shear connection is usually established by grouped headed studs, but possible alternative solution is to use bolted shear connectors. Welded headed studs and bolts (grade 8.8) are experimentally examined in the push-out tests (four tests on each). The same arrangement and dimensions of shear connectors (16 mm diameter and 100 mm height above flange) are considered and their resistances and behaviour are compared. Experimental results showed that headed studs and bolted shear connectors have similar shear resistance, while headed studs are more ductile. FEA is performed by ABAQUS/Explicit solver with damage material models to get more insight into behaviour of the specimens. FEA shows rather good agreement with experimental results. Influence of the bolt to hole clearance on the behaviour of specimens with bolted shear connectors is analysed and discussed.

Current design codes on stud shear connectors have clear limitations to cover new details of stud shear connection. New trends of stud shear connection are large diameter up to 30mm, clustered studs, different material for bearing, mixed arrangement with lying and vertical studs and confinement details. A research program was started to develop a separate design code on steel-concrete composite structures covering building and bridge structures in Korea. In order to improve current design provisions of stud shear connectors, experimental data on static and fatigue strength were collected, especially for new details. Collected data of experimental results, current design codes on static and fatigue strength of stud shear connection were investigated to expand their application limits. Additional coefficients for static strength are needed to consider new details. For the application of high strength material, shear stress range needs to be limited by 60% of static strength and bearing stress of concrete also need to be limited by 3 times of compressive strength of concrete to use current S-N curves. Shear connectors for precast decks, large studs greater than 27mm and clustered connectors with narrower stud spacing than 5 times of the diameter showed slight decrease of fatigue strength.

Composite one-way concrete slabs with profiled steel sheeting as permanent formwork are commonly used in the building construction industry. The steel sheeting supports the wet concrete of a cast-in-situ reinforced or post-tensioned concrete slab and, after the concrete sets, acts as external reinforcement. In this type of slab, longitudinal shear failure between the concrete and the steel sheeting is the most common type of failure at the ultimate load stage. Design codes require the experimental evaluation of the longitudinal shear capacity of each type of steel decking using full scale tests in simple-span slabs. There is no procedure in current codes to evaluate the longitudinal strength of continuous composite slabs and this is often assessed by full scale tests. This paper presents the results of three full-scale tests on continuous composite concrete slabs cast with using trapezoidal steel decking profile (KF70) that is widely used in Australia. Slab specimens were tested in four-point bending at each span with shear spans of span/4.The longitudinal shear failure of each slab is evaluated and the measured mid-span deflection, the end slip and the mid-span steel and concrete strains are also presented and discussed. The slabs are modelled in a finite element (FE) software package using interface elements to model the contact between the steel decking and concrete slab.

The use of composite slabs is common in the international area and is generally used in office and industrial buildings. Especially the advantages in weight support the use of the composite slab in case of refurbishment. The demand of sustainable solutions promotes the exploration of lightweight composite slabs by substitution of the normal weight concrete by concrete with a dry density between 1,400 kg/dm³ and 1600 kg/dm³. First tests have shown an unexpected failure mode due to the specific properties of lightweight aggregate concrete and its combination with composite sheets. In bending tests of composite slabs with lightweight aggregate concrete (LWAC), the failure was initiated by inclined bending cracks with a vertical offset of the crack surfaces and local buckling of the web of the composite sheet in the decisive crack. The known failure mode of specimens with normal weight concrete (NWAC) could not be validated in these tests. By an examination using the European regulations for the dimensioning of shear loaded concrete beams, a safety deficit about 20 % could be detected. Against this background at the University of Kaiserslautern, a new approach was developed to allow a safe determination of the shear capacity. The concept is comparable to different types of concrete and will be shown in this paper.

Composite slabs using cold-formed profiled steel sheeting have proved popular in multi-storey steel-framed buildings. This paper presents a comprehensive test programme that considers the performance of a modern trapezoidal profiled sheeting using Australasian 550 N/mm² high strength steel, compared to that exhibited by the same profile using European 350 N/mm² steel. Although the ductility of the Australasian steel is low, from composite slab tests it was found that the longitudinal shear behaviour could be considered ductile according to the Eurocode 4 requirements. As a consequence of this, the partial connection method was permitted. However, from the test results presented in this paper, it is shown that the rules given in Eurocode 4, Annex B.3.1 for a reduced investigation lead to unconservative results and should be revised. To remedy this situation, an amendment is proposed.

An experimental study was conducted on steel fibre-reinforced concrete (SFRC) composite slabs to quantify crack width resulting from shrinkage and gravity loading. Ten full scale slab specimens were evaluated with different types of bond between the concrete and deck (e.g., greased, unembossed deck, regular deck) and different amounts of concrete reinforcement (e.g., mesh, steel fibre). Concrete shrinkage was measured and monitored over a period of 74 days, and then slabs were tested under increasing load. Each was continuous over two spans and two line loads were applied on each span. Relationships between crack size/distribution were obtained for each slab for different levels of applied load.

This paper presents an experimental study and an assessment of the test results on composite slabs with profiled steel sheeting performed at Zurich airport in conjunction with the conversion of Terminal B. The structure was built in 1974 with composite floor slabs, a steel frame with stub-girder beams, and hot-rolled steel columns as supporting structure. The experimental investigation focused on the bond behaviour of the composite slabs and the influence of the 35 years service life. Ten large-scale in situ tests were carried out on simple beams with different shear span lengths to evaluate the longitudinal shear capacity. In addition, tests on two-span continuous beams and punching shear tests were performed. The data obtained by the tests enabled the assessment of the slabs. The assessment shows that the profiled steel sheeting after 35 years in use still features good longitudinal shear strength and is fit for reuse as slab of Terminal B of Zurich airport.

Post-tensioned composite steel-concrete slabs represent an innovative form of building floor application, which combine the structural advantages of the two most popular flooring systems, comprising post-tensioned slabs in the case of concrete structures and profiled composite slabs in the case of steel structures. The complex interaction between the profiled steel sheets and concrete is usually determined through a push test. A significant step toward understanding the bond behaviour is to generate a local bond stress-slip relationship. In this context, this paper presents results from a preliminary push test study using profiled steel sheets to determine the possible influence of prestress on the bond between the profiled steel sheets and concrete. The variables investigated in the study were (1) level of prestress and (2) height of push specimen. The results of this study indicate that prestress has a negative effect on the bond between the profiled steel sheets and concrete in post-tensioned composite slabs. This is an important finding, which needs to be considered in the ultimate strength of post-tensioned profiled composite slabs.