Full-scale Composite Beams Research Articles

Modelling of composite fin-plate connections under fire conditions using component-based method

Composite floor systems with fin-plate connections are widely used in multi-storey buildings, but there is currently no reported research on the development of a component-based model of a fin-plate connection at the beam-column interface that includes the effect of slab continuity above the fin-plate connection. In this research, a component-based model is developed to simulate a composite fin-plate connection. The component-based composite fin-plate connection model is able to simulate the slab continuity when installed at the beam-to-column interface of a composite floor system model. Fracture criteria for the plates and bolts of the fin-plate connection are adopted in the model to simulate connection failure. The component-based composite fin-plate connection model has been implemented in the software Vulcan, and is validated against a range of existing results, covering tests of individual fin-plate connections at ambient and constant high temperatures, subjected to combinations of tensile force, shear force and moment.The element is also used to simulate a test in which fin-plate connections were implemented at both ends of a composite beam with slab continuity, and subjected to elevated temperatures. The Vulcan modelling results show good comparison with the test results. The proposed component-based composite fin-plate connection model is shown to be a reliable tool to enable the performance-based finite element modelling of full-scale composite beams with fin-plate connections under fire conditions. Subsequently, parametric studies are carried out to investigate the influence of the key parameters, axial restraint stiffness and reinforcement ratio, on the behaviour of the composite beam and the connection force distribution, as well as to compare the very dissimilar structural responses of bare-steel and composite beams with the same geometries and loading conditions in fire.

Experimental and numerical study on the lateral torsional buckling of full-scale steel-timber composite beams

The lateral torsional buckling (LTB) of steel-timber composite (STC) beam with partial interaction was investigated in this paper. The composite beam is constructed by connecting the timber to both flanges of the H-shaped steel with bolts or screws. Twelve push-out specimens were designed to evaluate the shear performance of bolt or screw connectors. It was shown that the slip stiffness and the shear bearing capacity of the connectors increased with the thickness of timber increasing. Then, eight full-scale composite beams with lengths of 6000 mm were studied through bending tests and compared to a bare steel beam. The experimental behaviors of the specimens were identified, including the failure mode, load-deflection relationship and load-strain response. The LTB phenomenon and composite action were discussed by analyzing the strain distribution, stiffness and strength. The results demonstrated that the STC beams fastened with bolts or screws displayed partial composite action. Although the stiffness of the composite beam showed little augmentation, the maximum strength of the composite beam substantially increased by suppressing the LTB phenomenon. A finite element analysis was conducted to reveal the failure mechanism of the specimens with different geometric and physical parameters, including the number of timber layers, the interface shear stiffness and the initial imperfection. It was found that increasing the number of timber layers in the upper flange suppressed the lateral torsional buckling, and the interface shear stiffness was the key factor to control the stiffness and failure modes of STC beams.

Full-scale testing of adhesively bonded timber-concrete composite beams

This paper presents new findings on adhesively bonded timber-concrete composites with prefabricated concrete parts. Hereby, timber and concrete are bonded solely with adhesive and no metallic connectors have been used. Because the achievement of a continuous bond proved to be a critical point in past studies, special attention is given to that issue. The application procedure of the adhesives is investigated in small-scale bond samples and the manufacturing process in full-scale composite beams with a span of 8 m and a comparatively new polymer mortar is used as adhesive as well as a common epoxy resin. Both adhesives proved to be suitable, although polymer mortars showed strong advantages in terms of applicability and bridging of gaps in comparison to the less viscous epoxy adhesive. The full-scale beams are tested under quasi-static and cyclic loading. The failure occurred more as a bending failure of the timber or compression failure of the concrete. A full bond could be achieved at all full-scale beams. Moreover, an analytical and a finite element model for the calculation of composite beams are presented and validated. It could be seen, that both deformation behavior and failure load are in good accordance with the test results.

Damage identification of steel-concrete composite beams based on modal strain energy changes through general regression neural network

This paper presents a novel method for damage identification of steel-concrete composite beams based on modal strain energy (MSE) changes through general regression neural network (GRNN). A finite element (FE) model was developed using two Euler-Bernoulli beam elements as steel beam and concrete slab layers which are coupled by incorporating a deformable shear connection layer distributed at their interface. The connection layer was modelled as a uniform spring that enables both longitudinal slip and vertical uplift between the two components. The FE model was validated using experimental results of a full-scale composite beam in the laboratory. Three damage indices were defined as the elemental stiffness reduction in the steel, concrete and shear connection layers, respectively. A damage identification approach was developed to investigate the sensitivity of eigenvalues to damage in the composite interface. Then, MSEs change ratios were selected as the features for identifying structural damage in the composite layers. Principle component analysis was utilised to reduce the dimensionality of the large data features obtained from modal analysis leading to determining the main features for structural damage identification. The low dimensional data were employed as the input for the GRNN. Different damage cases were investigated, and the damage vectors were defined as the outputs of GRNN. The results show that the proposed method is efficient and reliable to identify damage in the composite beam with a few low vibration modes, even though small damage in the composite layers does not significantly affect these modes.

Lightweight and slender timber-concrete composite floors made of CLT-HPC and CLT-UHPC with ductile notch connectors

Cross-Laminated Timber (CLT) structures have been emerging worldwide for residential floors in multi-storey buildings thanks to their lightness, fast construction and low ecological footprint. This work aims at fostering this application, which is often limited by vibrational and deflection limits, by investigating composite slab floors made of CLT and High-Performance Concrete (HPC) slab as well as CLT and Ultra High-Performance Fiber Reinforced Concrete (UHPFRC).Firstly, the composite floors CLT-HPC and CLT-UHPFRC with a span of 8 m were designed by considering a multicriteria analysis. To assure a certain structural ductility, previously developed ductile notch connectors were employed. As an economic choice, no shear reinforcement in the concrete slab was employed. Then, full-scale composite beams were fabricated in order to verify the predicted flexural behaviour and natural frequency. A numerical analysis was carried out to verify the connectors could effectively yield before the timber collapse. The comparison between the numerical simulation and the slip measurements confirmed that about 50% of the notch connections fully yielded and underwent inelastic deformation which favors the structural ductility. In the case of the CLT-HPC floor, a reduction of the notch contact surface due to the use of plastic sheet waterproofing as well as shear cracks developing in the concrete close to the notch corner both reduced the expected structural stiffness. Finally, the CLT-UHPFRC floor is endowed with outstanding values of slenderness ratio (∼35) and lightness (∼2 kPa), while eliminating the use of shear reinforcement and sheet waterproofing.

Static Performances of Timber- and Bamboo-Concrete Composite Beams: A Critical Review of Experimental Results

The use of composite beams made with traditional concrete and bio-based materials (such as timber and bamboo) is a valuable solution to reduce the environmental impact of the building sector. Timber-Concrete Composite (TCC) beams have been used for decades in structural applications such as new buildings, refurbishment of old timber structures, and bridges. Recently, different researchers suggested composite beams based on engineered bamboo, commonly named Bamboo-Concrete Composite (BCC) beams. This study presents a systematic comparison of structural performances and connection behavior of TCC and BCC beams under short-term static load. TCCs beams are compared to BCC ones using similar shear connectors. The most important aspects of the two composite systems are compared: mechanical behavior of connectors and structural behaviors of full-scale composite beams (e.g., failure modes, connection stiffness, connection shear strength, ultimate load-carrying capacity, maximum deflection and composite efficiency). This comprehensive review indicates that BCC beams have similar or even better structural performances compared with TCC.

Effect of reinforcement on the strength of the web opening in steel-concrete composite beam

The steel web of the composite beam is commonly perforated for ducts and pipes passing to save the space under the beam and keep the clearance of buildings. However, this could weaken the flexural performance and the load bearing capacity of the composite beam. The published research on the flexural behavior of composite beams with reinforced web openings is limited. In this study, five full-scale composite beams with reinforced web openings were designed and loaded by three-point bending to study the influences of the type and cross-sectional area of stiffeners on the flexural performance of composite beams. For the purpose of comparison, a similar composite beam was designed without the web opening and a composite beam with the web opening was constructed without the reinforcement. As revealed from the experimental findings, the web openings reinforced with longitudinal stiffeners considerably improved the ultimate bearing capacity of the composite beams. When the cross-sectional area of the double-sided longitudinal stiffeners reached the weakened area of the steel web opening, the ultimate bearing capacity of the composite beam with reinforced web opening was comparable to the normal composite beam without web opening. The web opening reinforced with transverse stiffeners failed to significantly improve the ultimate bearing capacity of the composite beam. Moreover, the analytical models were put forward for predicting the ultimate bearing capacity of the composite beams with reinforced web openings.

Progressive collapse resistance of framed buildings with partially encased composite beams

Several research contributions stemmed from the increasing interest in progressive collapse-resistant design and assessment of structures, which was driven by extreme events all around the world. Most of studies focused on the robustness of steel and reinforced concrete (RC) structures, highlighting a knowledge gap on the progressive collapse resistance of framed buildings with partially encased (PE) continuous composite beams, which are an attractive solution compared to, for instance, their cast-in-place RC counterparts.This paper presents the main outcomes of a numerical investigation that was aimed at evaluating/exploring the vertical load-carrying capacity of framed buildings with PE beams after column loss. A numerical fibre-based model was developed and successfully validated against experimental data on two full-scale composite beam specimens, indicating a high accuracy level of the models with displacement-based fibre elements. Then, a wide set of framed building structures with PE beams was generated according to Eurocodes, evaluating their progressive collapse resistance through the alternate load path method. Pushdown analysis was carried out to investigate the gravity load capacity under increasing downward displacement at the location of the removed column. Analysis results outline a huge sensitivity of progressive collapse resistance to the beam type (i.e. PE versus RC), beam depth and span length, with minor influence of longitudinal reinforcement in the case of PE beams. The peak load capacity under column loss was characterised at several limit states corresponding to increasing levels of damage, allowing the proposal of multiple regression models for progressive collapse design and assessment.

Study on composite beams with prefabricated steel bar truss concrete slabs and demountable shear connectors

In the conventional steel-concrete composite beams, the composite action is achieved by welded stud connectors which are encased into the cast-in-place concrete slab. This makes the deconstruction and reuse of the structural components almost impossible. A sustainable and prefabricated composite structural system was developed in this study wherein the steel beam is attached to the prefabricated steel-bars truss concrete slab using the demountable bolted connectors. Twelve push-out specimens were designed and tested to assess the shear behavior of the bolted connectors. The test results showed that the shear bearing capacity of the bolted connectors with the prefabricated steel-bars truss concrete slab increased 7.0% over that of the bolted connectors with the prefabricated normal concrete slab. Three full-scale composite beams with various shear connection ratios were constructed and loaded to failure. For direct comparison, a similar composite beam was constructed with the same section size and shear connectors, but using the cast-in-place concrete slab. The flexural capacity of the composite beams with 68% shear connection and full shear connection increased 9.8% and 15.8% compared to the composite beam with 46% shear connection, respectively. The mechanical behavior of the composite beam with the prefabricated concrete slab was comparable with that of the composite beam with cast-in-place concrete slab. The load carrying capacity of the composite beam can be predicted by the simplified model in Eurocode 4 and the plastic model.

Failure modes of fibre reinforced foamed urethane composite beams: Full-scale experimental determination

A new composite material ‘fibre-reinforced foamed urethane (FFU)’ has received a significant momentum for utilisation in railway industry. As structural crosstie beams in railway switches and crossings, the FFU material acts as a supporting beam that redistributes the wheel loads onto track support. It is considered as an essential component underpinning the safe and reliable operations of railway switches and crossings. The usage track record and the deterioration process of composite FFU materials are not well known and never been thoroughly investigated. Importantly, the failure behaviours of the safety–critical components can influence the functional constraints of the switches and crossings. Since the application of FFU is for structural purpose, it is very crucial to determine the structural failure modes of the materials so that engineers can adequately design and optimize the structural components. The aim of this investigation is to identify the failure modes of composite FFU beam used in railway industry. The full scale composite beams have been used for the experimental testing. The test methods have been arranged in accordance with European Standard EN 13230 to determine the failure condition. It is important to note that there is currently no design nor testing standards for composite materials in the railway industry. This has resulted in a poor understanding into the real behavior and safety margin of the components in the real world. In fact, without the design concept, the safety margin cannot be scientifically determined. On this ground, this study is the world first to investigate the failure mode of the FFU composite beams. The insight into structural behavior of the full-scale FFU composites will enable better design and appropriate testing method for the composites in industry. Based on the experimental results, it is found that FFU composites can fail in brittle mode of failure at around 132 kN. This implies that the insight into flexural behaviours of the materials might not be sufficient for real-world design and application. Shear tests and its performance indicator might be required to enable safety for the public.

Experimental study of composite beams having a precast geopolymer concrete slab and deconstructable bolted shear connectors

Traditional steel–concrete composite beams are known to exhibit excellent structural characteristics, in terms of their stiffness and strength, when compared with bare steel or reinforced concrete beams. However, within current paradigms of lowering carbon emissions and enhancing the possibly of material recycling, such traditional composite beams cannot be deconstructed easily and their elements are not recyclable because they rely on welded headed stud connectors that are encased within cast in situ concrete to achieve the necessary shear connection. This paper presents the detailed results of quasi-static tests conducted on full-scale composite beams as part of a novel deconstructable and sustainable structural system. For this system, precast concrete slabs are attached to a steel beam using tensioned high-strength friction-grip bolts in clearance holes as the elements to provide the shear connection. The precast slabs are made using geopolymer concrete in lieu of concrete made from ordinary Portland cement, whose manufacture is a major contributor to anthropogenic CO2 emissions worldwide, thereby enhancing the low-carbon attributes of the structural system. The test results demonstrate the very significant ductility of the beams, with substantial interface slips being developed and sustained at loads close to the ultimate strength limit state. The tension induced in the bolts provides sufficient frictional resistance between the precast slabs and steel beams to ensure that the composite system has full shear interaction throughout the range of service loading. It is also confirmed that composite beams with bolted shear connectors can be deconstructed easily at the end of their service life, with the slabs, steel beams and bolts being reusable in other structural applications.

COMPOSITE CONSTRUCTION OF COLD-FORMED STEEL (CFS) SECTION WITH HIGH STRENGTH BOLTED SHEAR CONNECTOR

Composite construction is well known to be effectively used in the construction of buildings and bridges using hot rolled steel (HRS) and headed studs connectors. The shear connectors provides the enhancement as established in current design codes. In this paper, the shear connection mechanism was proposed using high strength bolted shear connector to provide composite action between concrete and the steel section. The conventional headed stud shear connector was eliminated since Cold-formed steel (CFS) was used and welding was not practically possible due to thinness nature of the CFS section. Therefore, in this study investigation was carried out on the strength capacity, ductility and the ultimate flexural capacity of the proposed high strength bolted shear connector and the composite beam specimens respectively. Four push-out and two full-scale composite beam specimens were fabricated using high strength M16 bolted shear connector of Grade 8.8 connected to the top flanges of the CFS I-section and tested to failure using push-out and four-point bending tests respectively. The results show that ultimate load and ultimate moment capacities of the proposed system were significantly improved by using the proposed connectors. The experimental results were compared with theoretical results based on the provision of Eurocode 4, and good agreement between the results was observed. In conclusion, compared results proved that the ultimate moment capacity of the proposed composite beams can be estimated efficiently by using the constitutive laws as prescribed by Eurocodes and British standards.

Design and evaluation of bonded composite glass beams

Glass can be combined effectively with another high-strength material, and a maximally efficient interaction between the two structural elements can be achieved. This paper deals with adhesively bonded steel–glass composite I-section beams, where the web is made of glass and the flanges are manufactured from steel. The paper describes the design procedure and presents a static evaluation, taking into account many influencing factors, such as the semi-rigidity of the adhesive layer, which is the key element in the horizontal shear contraction between the glass web and the steel flanges. Experimental research on full-scale composite beams with a span of 4 m is performed and evaluated in a laboratory at CTU in Prague. Analytical approaches for practical design are determined on the basis of these investigations, and are supported by many numerical studies. Adhesive producers (in the past mainly interested in the industrial application of their products) are now attempting to improve the properties of adhesives that can play a real load-bearing role in the joint. The procedure for including a new adhesive in an analytical approach is also described here.

Behaviour and design of composite beams subjected to sagging bending and axial compression

This paper presents an experimental and numerical study on the ultimate strength of steel–concrete composite beams subjected to the combined effects of sagging (or positive) bending and axial compression. Six full-scale composite beams were tested experimentally under sagging bending and increasing levels of axial compression. A nonlinear finite element model was also developed and found to be capable of accurately predicting the nonlinear response and the combined strength of the tested composite beams. The numerical model was then used to carry out a series of parametric analyses on a range of composite sections commonly used in practice. It was found that the sagging moment resistance of a composite beam is not reduced under low-to-moderate axial compression, while it significantly deteriorates under high axial compression. Sectional rigid plastic analyses confirmed the experimental results. The moment–axial force interaction does not change significantly between full and partial shear connection. Based on the experimental and numerical results, a sagging moment–axial compression interaction law is proposed which will allow for a more efficient design of composite beams.

Structural efficiency of full-scale timber–concrete composite beams strengthened with fiberglass reinforced polymer

The objective of this article was to experimentally evaluate timber–concrete composite beams in two different situations – with and without glass fiber reinforced polymer (GFRP). Four full-scale composite beams (5.4m in length) were produced, two of which had reinforcement (nominal thickness of 10mm) and two with no reinforcement. The fiberglass reinforcement was formed from the impregnation of unidirectional fiberglass cloth – effective thickness of 0.5mm – with epoxy resin. The connection system consisted of steel hooks inclined at 45 degrees, bonded with epoxy adhesive to the holes previously drilled on the wood, whose apparent density at 12% moisture content was 0.79g/cm3. The reinforced timber–concrete composite beams tested had performance efficiency of 79% and average rupture strength of 142.5kN. Finally, the reinforced timber–concrete composite beams were analytically evaluated using the proposed method in Eurocode5, showing reasonable agreement with the experimental results.

Flexural Behavior of Hybrid Composite Beams

This paper presents the development of composite beams, which consist of hybrid carbon and glass fiber-reinforced polymer (FRP) I-beams and precast, ultra-high-performance, fiber-reinforced concrete (UHPFRC) slabs. Hybrid FRPs (HFRPs) provide the advantage of high resistance to corrosion, while UHPFRC has great strength and durability. The combination of these two materials is expected to benefit structures subjected to severe environmental conditions and to respond to the need for accelerated bridge construction. Three full-scale composite beams with varied UHPFRC slab width were tested under four-point flexural loading. Bolt shear connectors with and without epoxy bonding were used in the tested beams. The bolt shear connectors and epoxy were used to resist the horizontal shear flow at the interface between the HFRP I-beam and the UHPFRC slab. The composite action between the HFRP I-beam and UHPFRC slab was investigated. The test results showed that all of the composite beams exhibited significant improvements in stiffness and strength properties, above those of single HFRP I-beams without a UHPFRC slab. A fiber model was developed to predict the strength and stiffness of the composite beam, and the model accuracy was verified. Good agreement was found between the experimental and analytical results. The high tensile strength of a carbon FRP in an HFRP tensile flange could be used effectively, and the delamination failure of an HFRP compressive flange could be prevented through the addition of a UHPFRC slab on the top flange of the HFRP I-beam. The study revealed that HFRP–UHPFRC beams were efficient and could provide a competitive, cost-effective, and sustainable solution to bridge structures.

Simplified nonlinear simulation of steel–concrete composite beams

A computationally efficient macro-model approach is proposed for investigating the nonlinear response of steel–concrete composite beams. The methodology accounts for material nonlinearity and interface slip between the concrete slab and the steel beam. The validity of the technique is evaluated through comparison of the macro-model-based simulations with results obtained from experimental testing of composite beams. Four full scale composite beams are tested under monotonic positive and negative bending. The results show that the proposed macro-element-model can capture the essential characteristics of the nonlinear load–deformation response of composite beams. Such an approach is a compromise between simplicity and accuracy and a viable alternative to detailed finite elements analysis. Additionally, a parametric study, including the compressive strength of slab concrete, the yield strength of the steel flanges and web, and the shear connection degree, of the steel–concrete composite beams subjected to positive moment is conducted utilizing the numerical macro-model proposed. The slips and their influences on the behaviors of composite beams during loading process have been analyzed.

Full-Scale Testing for Composite Slab/Beam Systems Made with Extended Stud Spacing

Investigation of the background of the 610 mm (24 in.) spacing of stud shear connectors showed that this limit was set on the basis of a small amount of testing of beams with spacing greater than this limit. The literature search showed that some attempts have been recently made to extend this limit. One of the objectives of the NCHRP 12-65 research project was to investigate the possibility of extending this limit to 1,220 mm (48 in.) for cluster of studs used for precast concrete panels made composite with steel I-beams. The experimental investigation included testing of push-off specimens and full-scale composite beams. Results of the push-off specimens have shown that the fatigue loading has no detrimental effect on the load-slip relationship when the number of studs is doubled per cluster. This paper covers the second part of the experimental investigation, which is fatigue and ultimate testing of full-scale composite beams. The full-scale testing has proven that full-composite action between precast concrete panels and steel girders can be achieved when the spacing between the stud clusters is extended up to 1,220 mm (48 in.).

Development of prefabricated timber–concrete composite floor systems

The timber–concrete composite structure consists of timber joists or beams effectively interconnected to a concrete slab cast on top of the timber members. This type of structure is finding new applications in multi-storey buildings and short-span bridges. Most of the research performed to date has focused on systems where ‘wet' concrete is cast on top of timber beams with mounted connectors. This paper presents a novel composite system where the concrete slab is prefabricated off-site with connectors already embedded and then connected to the timber joists on site. The advantages of this method include reduced cost and better quality control of the materials, absence of ‘wet' components on site during building erection and reduced concrete shrinkage effects on the composite beam. The paper reports an overview of a pilot research project conducted at Luleå University of Technology, Sweden, which includes direct shear tests to failure of different connection systems, bending tests to failure, dynamic (vibration) tests and long-term tests under sustained load of full-scale composite beams. The paper also reports the mechanical properties of the connection, which can be used within a simple design method given in Eurocode 5. The economic advantages of prefabrication and the possibility of demounting the structure make the proposed floor system very promising.

Correlation of Beam Tests with Pushout Tests in Steel-Concrete Composite Beams

Controversy has risen about the suitability of small-scaled pushout tests to satisfactorily model the behavior of shear connections in composite beams. However, the determination of the strength of the shear connectors from full-scale composite beam tests is expensive, complicated, and subject to modeling inaccuracies. The results of several composite beam tests incorporating trapezoidal steel decking are presented along with the results of companion pushout tests. These were especially designed to deliver insight into the ductility of the shear connection when subject to the so-called “brittle” failure modes of the concrete slab observed in small-scale pushout tests, and to examine the suitability of novel reinforcing measures such as waveform reinforcement components or stud performance-enhancing devices. The comparison of the shear connection performance in both the carefully conducted pushout tests where no additional lateral restraints were employed and the beam tests demonstrated that the failure modes experienced were identical, the load-slip behavior was also similar, and comparable connector strengths were achieved. The requirement of sufficiently ductile shear connection behavior in achieving a satisfactory composite beam performance was also established in these tests.