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An innovative form of steel–concrete composite beam, the steel–coarse aggregate reactive powder concrete (CA-RPC) composite beam with uplift-restricted and slip-permitted (URSP) connectors, is introduced in this paper. The aim is to enhance the cracking resistance under negative bending moments, which is a difficult problem for traditional composite beams, and to make the cost lower than using ordinary reactive powder concrete (RPC). An experimental investigation of the behavior of six specimens of simply supported steel–CA-RPC composite beams with URSP connectors under negative bending moments is presented in this paper. The test results validated that the cracking load of steel–CA-RPC composite beams could be approximately three times that of the ordinary steel–concrete composite beams while the bearing capacity and stiffness are almost the same. A numerical model, using the concrete damaged plasticity (CDP) model to simulate the behavior of the CA-RPC material, was proposed and successfully calculated the overall load–displacement relationship of the composite beams with sufficient accuracy compared with the experimental results, and the distribution of cracks and the failure mode of the beams could also be captured by this model. Furthermore, a parametric analysis was carried out to find out how the application of prestress, CA-RPC, and URSP connectors could affect the cracking resistance of the composite beams, and the results indicated that using CA-RPC and prestress made the main contributions and that the usage of URSP could boost the effect of the other two factors. The plastic resistance moment of the beams was also compared with the calculation results using the methods introduced in Eurocode 4, and it was proved that the calculation results were lower than the experimental results by approximately 10%, which meant that the method was reliable for this kind of composite beam. [ABSTRACT FROM AUTHOR]

This paper investigates the behaviors of different types of prestressed concrete beams utilizing fully encased cold‐ or hot‐formed steel joists. Twelve types divided into two sets of composite beams are assessed. Set 1 is composed of six beams utilizing cold‐formed steel (CFS) joists distinguished by the cross‐sectional steel‐to‐concrete ratios of 1%, 2%, and 3%, and the presence or absence of web openings. Set 2 has the similar composition but utilizes hot‐formed steel joists. Four‐point and three‐point bending tests were conducted at the mid‐span of the composite concrete beams. Key properties, such as strength, stiffness, flexural load capacity, ductility, energy absorption capacity, and failure modes, were used in the analysis. It was found that the specimens with CFS I‐beam joists provided better performance compared to those with hot‐formed steel joists. Also, the existence of web openings in the encased CFS beams enhances the ductility and energy absorption of the composite concrete beams. [ABSTRACT FROM AUTHOR]

To investigate the shear performance of assembled bamboo scrimber (BS)-lightweight concrete (LC) connection systems, three groups of nine BS-LC shear connections were fabricated in this work using BS, LC, dowels, and grout. The experimental parameters included the dowel diameter and fabrication process (cast-in-place vs. assembly). Push-out tests were conducted on the specimens, and traditional linear variable displacement transducer (LVDT) measurements and the advanced digital image correlation (DIC) technique were employed to determine performance indicators such as the cross-section slip of composite members. Subsequently, the method for calculating the shear capacity of assembled BS-LC connection systems was theoretically analyzed. The research results showed that the load-slip curves measured by DIC were highly correlated with those measured by LVDT, thus, validating the reliability of the DIC data. According to the DIC data, the variations in slip of the shear connection over the interface height were further analyzed. An equation for calculating the shear capacity of dowel shear connectors was proposed based on theoretical analysis with comprehensive consideration of the experimental indicators such as the failure mode, load-slip curve, shear stiffness, and shear capacity of the specimens. The theoretical calculation values were in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

Existing studies have proved that interfaces between the prefabricated layer and the cast‐in‐place layer significantly affect the static performance of prefabricated concrete structures using the wet connection method, but little has been known about the fatigue performance, especially at high load levels. This study investigated the fatigue behavior of prefabricated composite concrete beams under negative bending moment induced by the high‐stress level cyclic load. Fifteen composite T‐beams with three different designed sections were tested. The failure mode, cracking and deflection behavior, steel strain development, and the new‐old concrete interfacial deformation were recorded and analyzed. It was found that the stress redistribution occurred with the debonding cracks generated at the new‐old concrete interface, causing the degradation of the static and fatigue performance. Setting interfacial shear keys could prevent such debonding failure at static and low cyclic loading levels. Meanwhile, the corresponding mechanisms were verified through cross‐sectional analysis. [ABSTRACT FROM AUTHOR]

This numerical study presented and analysed a new technic of castellated steel beam "Alternate Closed Opening Castellated Beam" applied only to double steel channel shapes connected back to back. ABAQUS/2019 program employed to create modelling and analysis for two groups of models with the same length and conditions of loading. The first group has three noncomposite beam models: the first reference model without castellated, the second model with normal castellated and the third model with new castellated, also the second group has three composite beam models: the first reference model without castellated, second model with normal castellated and the third model with the new castellated. According to the analysis results; For the first noncompsite group, ultimate load for the second and third models increased by 8.84% and 16.63%, respectively, compared to the reference model, with local buckling in the top flanges under concentrated loads and lateral-torsional buckling as the failure modes. For the second composite group, the ultimate load for the second and third models increased by 41.83% and 62.19%, respectively, compared to the first reference model, with the flexural mechanism as the main failure mode. This enhancement in the load-carrying capacities of the new Alternate Closed Opening Castellated Beams is due to the limit states mode of failures resulting from web holes. [ABSTRACT FROM AUTHOR]

Ultra‐high performance concrete (UHPC) prefabricated beams are competitive in accelerated bridge construction. However, their broader application has been hindered by limited large‐scale tests and inaccurate design methods. To fill this gap, the authors conducted an experimental investigation on the shear and flexural performance of UHPC pi‐beams using two full‐scale specimens. One specimen was a precast UHPC beam, while the other was a composite beam with a normal concrete slab on the UHPC beam. The primary focus was on crack propagation, ultimate capacities, and failure modes. To complement the experimental findings, the extended finite element method (XFEM) was developed as a numerical approach. Nevertheless, relying solely on XFEM to understand real structural behavior is prone to misinterpretations. Moreover, the shear and flexural capacities were evaluated using existing codes and compared with the experimental results. The comparisons revealed that the predictions of shear capacities were at least 15% lower than the experimental values, whereas the flexural capacities showed acceptable agreement. To address this, the authors introduced the limit equilibrium method, leading to a more accurate prediction of shear capacity for UHPC beams with a deviation of <2%. [ABSTRACT FROM AUTHOR]

Polyvinyl alcohol‐engineered cementitious composite (PVA‐ECC) exhibits strain hardening and multiple cracking characteristics under tension. Its superior tensile behavior may also influence the flexural behavior of reinforced PVA‐ECC beams. This paper investigates the load capacity and failure mode of reinforced PVA‐ECC beams in bending. Seven beams with different tensile reinforcement ratios, including six PVA‐ECC beams and one conventional concrete beam, were tested in the experimental program. The influence of reinforcement ratio on load capacity and failure characteristics was discussed in detail. Test results showed that with increasing reinforcement ratio, the ultimate load of beams was increased, but the failure mode was changed from fracture of PVA‐ECC in the tension zone to crushing in the compression zone, thereby limiting the full development of beam ductility. An analytical model is proposed to calculate the load and the vertical deflection of beams. In the model, the tension‐stiffening effect of reinforcement after cracking of PVA‐ECC is considered by defining the bond–slip relationship of reinforcement embedded in PVA‐ECC. Comparisons are made between experimental results in the literature and those calculated by using the analytical model to show the accuracy of the model in predicting the load–deflection relationship, the moment–rotation relationship, and the moment–curvature relationship. [ABSTRACT FROM AUTHOR]

Ultra High Performance Concrete (UHPC) has gradually become the most promising high-performance material, and has achieved good results in the field of impact and explosion protection engineering. In general, normal reinforced concrete (NC) beams subjected to impact load are prone to local punching shear failure. Although pure UHPC beams can improve their impact performance, their further application is limited by the high cost. In order to achieve the balance between impact resistance and economy, this study puts forward the design scheme of local replacement and wrapping with UHPC to improve the impact resistance of reinforced concrete beams. In this work, the different research conditions including NC beam, UHPC beam and NC-UHPC composite beam are designed, and the impact resistance of specimens is compared and analyzed. The results show that UHPC local replacement scheme can effectively avoid local punching shear failure of beams. As for the UHPC wrapping scheme, the failure mode of the beam changes from punching shear failure to bending failure. Compared with NC beams, two schemes can effectively reduce the peak displacement and residual displacement in the mid-span. The peak displacement and residual displacement in the mid-span of the UHPC local replacement beam are smaller than that of UHPC wrapping schemes, and the mid-span bearing capacity is better. In this work, it is recommended to take a local replacement length greater than 2 times the beam height to avoid local punching shear failure. [ABSTRACT FROM AUTHOR]

The flexural performance of a spliced composite slim beam with a slotted web (SCSB-SW) was assessed and prediction formulae of flexural capacity and initial stiffness for the beam were deduced. Through a four-point bending test, the flexural performance of the SCSB-SW was preliminary studied. The experimental results indicated that the section of the SCSB-SW conformed to the plane section assumption in the elastic stage. The beam failed in a ductile failure mode while there was no obvious relative slip between the steel beam and concrete slab in the failure stage. Finite-element models were developed and validated using the test results. A parametric analysis revealed that even if the cross-sectional dimensions and the position of the neutral axis in the beam are changed, the results predicted by the formulae still matched the numerical results well. The material strength, the thickness of the bottom flange of the steel beam and the concrete slab dimensions were found to play key roles in the flexural capacity of the beam, whereas the compressive strength grade of the concrete, the depth of the steel beam web and the dimensions of the concrete flange have significant effects on the initial stiffness of the beam. [ABSTRACT FROM AUTHOR]

A novel FRP/steel-concrete composite beam consisting of concrete slab and innovative hybrid FRP/steel hollow box shell takes full advantage of inherent and complementary properties of FRP, steel and concrete. To facilitate the practical application of this novel FRP/steel-concrete composite beam, preliminary design concepts were offered while analytical equations were derived to evaluate the flexural performance of the composite beam based on analysis of typical failure modes. Three FRP/steel-concrete composite beams with different steel volume fraction had been devised by the proposed design method, and four-point bending tests were conducted to investigate the failure mode, ultimate flexural capacity, deflection and interface slip. The practical composite beams exhibited satisfying structural behavior during the tests, while a fairly good agreement with the experimental results and the estimated values confirmed the reliability and feasibility of the preliminary design method. [ABSTRACT FROM AUTHOR]

Test results of steel-ultra high performance concrete (UHPC) composite beams with welded steel shear keys (SSKs) under four-point bending are presented in this paper. The objective of the investigation is to reduce the self-weight and manufacturing cost of large-span structures. The study investigates the effects of strength of concrete slab, type, spacing and size of SSK, and concrete slab height and width on flexural behavior of composite beams. The experimental results demonstrate that enhancing concrete strength, reducing SSK spacing, increasing concrete slab size, and using large-size SSK can all significantly enhance the flexural performance. The composite beams with welded SSK exhibit a maximum relative slip of less than 4 mm, while the counterpart with welded bolts has a maximum relative slip greater than 4 mm. The study shows that the welded SSK is more effective than welded bolts in improving the interface shear performance of composite beams and improving the stiffness and load capacity. Additionally, the study defines four failure modes of steel-UHPC composite beams, and the formulae for flexural capacity is developed based on the reasonable basic assumptions. The calculated results fit well with the tested results. The research findings can be provided as a technical support for the design and application of steel-UHPC composite beams. • The flexural behavior of steel-ultra high performance concrete composite beams with welded steel shear keys was tested. • Effects of concrete slab and steel shear key on flexural behaviour of composite beams were studied. • Four failure modes of steel-UHPC composite beams were defined, and the formulae for flexural capacity is developed. [ABSTRACT FROM AUTHOR]

Conventional concrete structures often rely on labor-intensive and wasteful formwork systems. In contrast, 3D concrete printing (3DCP) technology offers a more efficient alternative for fabricating complex-shaped permanent formwork. This study fabricates innovative composite beams using 3D-printed ultra-high-performance strain-hardening cementitious composites (UHP-SHCC) as permanent formwork, followed by casting infill materials. The spatially tailored fiber dosage distribution in the 3D-printed UHP-SHCC permanent formwork enables the performance optimization of the composite beam. The flexural behavior of three such formed composite beams is evaluated using four-point bending tests. A reference beam with homogeneous fiber distribution in the UHP-SHCC formwork is also tested for comparison. The failure mode, overall load–displacement response, and cracking performance of four beams are comprehensively characterized and compared. The results reveal that employing graded fiber dosages in UHP-SHCC formwork enhances fiber efficiency and structural performance while reducing fiber usage and material costs. The use of 3D-printed UHP-SHCC formwork with graded fiber distribution, despite using 25% less fibers and reducing the material cost by 12.8%, leads to a 65.6% increase in strength and over 50% increase in energy absorption, or a 77.4% increase in ultimate displacement with comparable peak load to the reference beam with homogeneous fiber distribution. [ABSTRACT FROM AUTHOR]

Using precast concrete floors can greatly improve the construction efficiency of steel structures, and the development of the connection between precast slabs affects the application of precast concrete floors in steel structures. In this paper, a new connection between the precast concrete floor and steel beam is proposed. The bending capacity of the connection was investigated through experiments, and compared with that of the cast-in-place floor. The test results showed that the reliability of the new connection was excellent, and the bending capacity of the floor with this connection is basically the same as that of the cast-in-place floor. The finite element software ABAQUS was employed to simulate the bending behavior of the new connection floor and cast-in-place floor, and the feasibility of the model was verified by comparing it with the experimental results. The model was used to analyze the structural response of the two types of composite beams composed of new connections and precast floor, cast-in-place floor, and steel beam, respectively. The load-bearing capacity and failure modes of the two composite beams were compared. The results showed that the bearing capacity of the composite beam fabricated with the new connection can reach that of the cast-in-place floor composite beam. This is only a preliminary investigation about the new connection and there are some limitations as well. [ABSTRACT FROM AUTHOR]

Design for disassembly using deconstructable connections facilitates recycling and reusing of building materials and, therefore, reduces waste management problems at the end of service life. In this regard, a deconstructable timber-concrete composite connector using self-tapping screws has been developed at Aalto University. In the presented research, an experimental investigation was performed to further evaluate the effectiveness of this connector in fabricating deconstructable cross-laminated timber (CLT)-concrete composite floors. For this purpose, several CLT-concrete composite beams were fabricated using 5-layer CLT and low-shrinkage concrete. Each beam contained one row of connectors to represent a strip of a full-scale floor. The vibration performance, bending properties, interface slip, failure modes, and ease of disassembly of the beams were investigated. The results were compared with the ones from a reference group of beams fabricated with regular screws. Overall, the deconstructable beams performed exceptionally well by attaining 98.5% of the average bending stiffness of the regular beams. The load-carrying capacity was also similar but governed by the CLT plate. The vibration characteristics were comparable in both groups. After the bending test, the deconstructable beams were disassembled. Although the beams had been exposed to unproportionally large deformations under the bending load, the disassembly process was performed successfully. [ABSTRACT FROM AUTHOR]

This study presents an experimental investigation of the failure characteristics, interface slip, strain distribution, and load-deflection response of adhesively bonded timber-concrete composite (TCC) beams fabricated using wet or dry processes. A total of six adhesively bonded TCC beams were produced with a span of 3.2 m and subjected to four-point bending tests. Wet and dry fabricated TCC beams revealed distinct failure modes. The results emphasized the critical role of bonding integrity in ensuring effective composite action and shared contribution mechanism. Wet-fabricated TCC beams exhibited a rigid bonding characterized by a consistent neutral axis alignment and load distribution along the beam span, while dry-fabricated beams experienced interface separation and compromised load-shared contribution, resulting in a significant reduction of the ultimate bending capacity of TCC beams. The outcomes showed that wet and dry TCC beams exhibited comparable load-to-mid-span deflection responses before failure, highlighting uniform behaviour and alignment with fully composite characteristics under the imposed loads. Furthermore, an analytical model for calculating TCC beams is presented and validated. The foundation of the analytical model is established upon the γ-method derived from Eurocode 5. The analytical model is compared with experimental results, highlighting its reliability and precision. Load-deflection responses, bending strain distributions, and ultimate failure loads are accurately captured, affirming the model's capability to anticipate the TCC beam behaviour. • Reliability of glue connection in TCC structures. • Performance insight in wet vs. dry TCC beams. • Analytical model for TCC design. • TCC Structural performance and environmental impact. [ABSTRACT FROM AUTHOR]

Application of fiber‐reinforced polymer (FRP) reinforcement in concrete beams may cause large deflection and crack width, as well as low shear capacity and ductility due to relatively small stiffness of FRP materials. To avoid these unfavorable factors and evaluate the shear behavior of FRP‐reinforced structural members, a high‐performance strain‐hardening cementitious composite (SHCC) is introduced to substitute conventional concrete in reinforced beams, and four‐point bending test is conducted in this study. Six FRP‐reinforced SHCC beams with different transverse reinforcement ratios and shear spans, as well as one concrete reference beam, were tested. According to the test results, the FRP‐reinforced SHCC beam showed enhanced shear carrying capacity and superior ductility compared with the concrete beams. The shear span to effective depth ratio as well as the stirrup ratio has a great influence on the shear behavior of FRP‐reinforced SHCC beams, including the failure mode, load‐carrying capacity, crack propagation, and ductility. Finally, a simplified truss‐strut model for predicting shear carrying capacity of steel or FRP‐reinforced SHCC beams is proposed, and a good agreement is achieved with the experimental results. [ABSTRACT FROM AUTHOR]

This research investigated the flexural behavior of high-strength concrete beams reinforced with continuous basalt fiber-reinforced polymer (BFRP) bars and discrete steel fibers. Five concrete beams with the dimensions of 150 × 300 × 2100 mm3 were constructed and tested to failure under four-point bending cyclic loading. The specimens consisted of four BFRP-reinforced concrete beams with various reinforcement ratios (ρf), namely, 0.56%, 0.77%, 1.15%, and 1.65%, and one conventional steel-reinforced concrete beam for comparison purposes. The cracking behavior, failure modes, load-deflection behavior, residual deformation, and stiffness degradation of the beams were studied. Additionally, a deformation-based approach was used to analyze the deformability of the beams. The results show that an increase in the ρf effectively restrained the crack widths, deflections, and residual deformation while also enhancing the flexural bearing capacity of the beams. In comparison to the first displacement cycle, the bearing capacity dropped by 10% on average in the third cycle. The stiffness exhibited a fast to slow degradation trend until failure. The residual stiffnesses were higher in beams with a higher ρf. The over-reinforced beams had superior deformability than the under-reinforced beams, according to the deformability factors. [ABSTRACT FROM AUTHOR]

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Hybrid use of Carbon fiber reinforced polymer (CFRP) composites with conventional construction materials offers an ample opportunity to develop economical and high-performance structures. However, anchoring and debonding problems remains a challenge for the accomplishment of this technique. In this study, a novel application was implemented in which the CFRP sheet was integrated as internal flexural reinforcement for RC beams. The target was to evaluate the contribution of the CFRP sheet to the flexural performance and thus assess the efficiency of using the CFRP sheet as primary or supplemental flexural longitudinal steel reinforcement. CFRP sheet can be cut without difficulty to any width/length and then attaching them to the main steel bars without using epoxy. Similar to the longitudinal steel reinforcement, the CFRP strips work integrally with steel reinforcement as the concrete confines them. The investigated parameters are the number of CFRP layers, CFRP sheet length, strengthening type (internal or external strengthening). Therefore, the feasibility of internal strengthening for improving the behavior of RC beams is of vital interest. The performance of each beam was evaluated in terms of failure mode, load versus mid-span deflection curve, ultimate deflection, ultimate load capacity, stiffness, displacement ductility index, energy absorption, energy absorption ductility index, performance factor, and CFRP strain. The results show a significant improvement in the majority of the investigated parameters and show the effectiveness of internal strengthening. The internal strengthening provided external cracks arresting mechanism and even after reaching the ultimate load capacity. [ABSTRACT FROM AUTHOR]

New methods to provide shear strength on the cold-formed steel (CFS) lipped c-channel section composite beam encased with concrete partially is proposed using rebars embedded in concrete. The development of research on the CFS composite beams technology with partial encasement shows that the section of the composite beam encased with concrete partially can provide ductile flexural action for the composite beam. The application of profiled metal decking slabs in the composite beam is becoming increasingly popular compared to solid slabs. However, it has a detrimental effect on the structural behavior of a composite beam. This research is aimed primarily at presenting the behavior of the rebar shear connector to evaluated ductility, shear capacity, and modes of failure. Two samples using a rebar 12 mm in diameter in the profiled metal decking slabs and solid slabs were tested using the standard push-out test till failure. For the composite beam design, the proposed shear connector embedded in the slab concrete and the CFS encased with concrete partially used the test results' shear capacity, greater than the values as proposed by section 3.1, BS 5950. Due to rebars shear-off, the solid slab specimen failed with the highest load of 489.6 kN while the Profiled Metal Decking Slab specimen failed due to the formation of the cracks on the PMDS at 421.1 KN ultimate loading. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study of full-scale steel-concrete composite beams using truss-type shear connectors. The connector geometry is original and effective. It is made from traditional steel rebar used in reinforced concrete structures. When compared with the stud-shear connector, the truss-type shear connector has several advantages, including low cost, ease of installation, and high resistance, among others. Previous research on the truss-type shear connector has made use of the popular push-out test, a reduced-scale physical model. However, for a better understanding of the truss-type shear connector behavior and to make it reliable for engineering practice, the truss-type shear connector must be studied under more realistic working conditions. In that sense, this research presents an experimental study in which three full-scale tests of steel-concrete composite beams, using truss-type shear connectors, are carried out. In the experimental program, different shear connection degrees are considered. The experimental results showed that when the shear connection degree is decreased, there is a rise in slippage between the steel beam and the concrete slab and a drop in the ultimate load. In the tests, the measured values of the uplift separation between the steel beam and the concrete slab were in compliance with the Eurocode-4 specifications. The failure modes of the specimens were characterized by excessive yielding of the steel beam or by a combination of this and the failure of the connections. The resistance of the truss-type shear connector was successfully predicted using the equation developed by the authors. • Truss-type shear connectors are evaluated experimentally in full-scale steel-concrete composite beams. • It was experimentally found that the truss-type connector complies with Eurocode-4 specifications. • An equation for the shear resistance strength of the truss-type connector was verified experimentally. • The effectiveness of the truss-type shear connector and its potential to applications were demonstrated in this research. [ABSTRACT FROM AUTHOR]

Plate end debonding is a common failure mode for fiber reinforced polymer (FRP) strengthened beams. FRP sheets and shape memory alloy (SMA) composites can effectively slow down plate end debonding and improve beam ductility owing to the anchorage effect of SMA wires on the FRP ends. This work aims to comprehensively study the anchorage performance of FRP/SMA composite strengthened beams through both model analysis and experimental investigation. The plate end debonding strength models of existing FRP strengthened beams were initially summarized and analyzed, and an improved model was proposed to predict the debonding strength of FRP/SMA composite strengthened beams at the plate end. Moreover, the anchorage performance and flexural behavior of beams strengthened with carbon fiber reinforced polymer (CFRP) and SMA composites were studied through experiments. The failure mode of the FRP sheet strengthened beams was plate end debonding failure, while the plate end debonding failure of the CFRP/SMA composite strengthened beams occurred at the strengthening zone end, and the peeling failure was delayed owing to the anchorage effect of SMA wires on the ends of the strengthening CFRP sheets. The recovery effect of SMA wires could successfully introduce prestress into CFRP sheets. Moreover, the CFRP strain corresponding to plate end debonding increased because of the anchorage of SMA wires on the CFRP sheet in the strengthening zone. The strength and ductility of the CFRP/SMA composite strengthened beam significantly improved. The proposed model for predicting the plate end debonding strength of FRP/SMA composite strengthened beams was validated through experiments. • An improved model is proposed to predict the debonding strength of beams strengthened with FRP/SMA composites at the plate ends. • The debonding failure was delayed due to the anchorage effect of SMA wires on CFRP sheets in the strengthening zone. • The strength and ductility of the beam strengthened with CFRP/SMA composites have been significantly improved. • The proposed model for predicting the plate end debonding strength of FRP/SMA composite strengthened beams was validated through experiments. [ABSTRACT FROM AUTHOR]

In this study, experimental tests were performed to evaluate the shear performance of encased steel truss (EST) composite girders that can resist loads at construction and composite stages. Four full-scale EST composite girders were fabricated, where the truss type (Pratt truss and Warren truss) and presence of stirrups were set as main test variables. The test results showed that in specimens applied with the Pratt truss, horizontal shear cracking occurring along the interface between concrete and steel was the dominant failure mode. Based on the crack pattern and failure plane observed from the test, the horizontal shear strengths of the Pratt truss specimens were calculated, which provided conservative results. On the other hand, in the specimens with the Warren truss inside, the strengths of the specimens were governed by the shear failure occurring in the screw rod connecting the truss elements prior to the yielding of the diagonal member. The shear strengths of the Warren truss specimens calculated based on the shear failure of the screw rod were similar to that obtained from the test. [ABSTRACT FROM AUTHOR]

In this research paper, simulations on five specimens of square steel tube truss concrete beams with grouted chords were conducted by finite element analysis (FEA) software ABAQUS. Comparison of failure modes, vertical load-deflection curves, and steel tube strain variation with tests was done. The rationality and validity of the FEA models were also verified. On this basis, parameter analysis was carried out, and the influence of concrete strength, steel ratio of upper and lower chords, and spacing of steel tube truss joints on the vertical load-deflection curves were obtained. From the results of tests and parameter analysis, design formulae of flexural bearing capacity for composite beams were proposed based on the assumption that steel tubes are equivalent to ordinary longitudinal steel bars. Accordingly, the results indicated that the steel tubes of the upper chords in the composite beams cannot get yield for full sections due to the structural requirements; the steel tube of the lower chords will be the first to reach fully yielding and the upper concrete crushed subsequently, showing a failure mode analogous to that of the under-reinforced concrete beam; the steel ratio of lower chords is the primary factor affecting the flexural capacity of the normal section among the parameters; the calculation from the proposed design formulae for the flexural capacity of normal section is in agreement with the tests and simulations. This research could provide reference for the design of this kind of composite beam. [ABSTRACT FROM AUTHOR]

In the present investigation, the structural behavior of reinforced geopolymer concrete (RGPC) beams containing steel fiber has been studied. Four‐point flexural loading condition was applied in this experimental study; for testing the RGPC beams. The deflections of the RGPC were gauged at the mid‐span of the specimens. The crack patterns and failure mode of RGPC beam specimens were measured during the testing process. From these measurements, it has been observed that the steel fibers control cracking due to plastic and drying shrinkages. The length and width of cracks generally improved with the increment of steel fiber content. The findings also indicate that the flexural strength and elastic modulus of RGPC are remarkably enhanced due to the incorporation of steel fibers. Furthermore, the failure mode of RGPC is almost similar to the failure mode of conventional concrete. However, the RGPC performed better than the conventional concrete in terms of flexural strength and other mechanical properties. It has also been noticed that the increase of a/d ratio results in shifting the flexural failure mode in the mid‐span regions towards the support points. The experimental results have been compared with the relevant published literature as well as with the different standard codes. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation on reinforced concrete (RC) beams strengthened in shear with embedded through-section (ETS) steel and fiber reinforced polymer (FRP) bars anchored with and without a mechanical anchorage system. The responses of the beams, including the load–deflection relationship, crack patterns, modes of failure, and reinforcement strain, are discussed. In addition, the shear performances of different strengthening systems are analyzed by comparing the ETS cases with ordinary reinforcement techniques. The effects of different types of ETS strengthening are considered in the presence of varying numbers of steel stirrups. An investigation of the shear contribution of the strengthening bars is carried out to assess the applicability of existing models. An average strain equation for ETS-FRP bars is developed from original models. Comparisons of the results obtained from this paper with those reported in the literature demonstrate that the end anchored ETS strengthening system provides a significant improvement in the shear strengthening efficiency. Furthermore, the truss analogy combined with the developed average strain formulation is an effective method to predict the shear resisting force of anchored ETS-FRP bars in ETS-FRP strengthened beams. [ABSTRACT FROM AUTHOR]

Encased U-shaped steel concrete composite beam is a newly developed composite beam with extensive use. The section of the U-shaped beam is not closed and thus has limited constraints to internal concrete. The reinforced cast-in-place concrete slab in the upper part is not suitable for fabricated structures. To improve the adaptability of the U-shaped steel concrete composite beam in the fabricated structure, concrete composite beams stiffened by fabricated rebar truss with Ushaped steel girders was proposed. First, static loading tests were performed for the two proposed composed beams. Second, failure mode, force–displacement curve, depth of the compression zone, strain distribution, and the global performance of steel and concrete under positive and negative bending moments were compared and analyzed. Results demonstrate that the specimen under positive bending exhibits ductile failure mode and has strong deformation capacity with its ductility coefficient of up to 5.34, indicating that the proposed composite beam is simple and reasonable and has strong integrity. However, the specimen under negative bending is buckling. This study provides references for the popularization and application of the novel composite beam to the fabricated structural industry. [ABSTRACT FROM AUTHOR]

After using Ultra-High Performance Concrete (UHPC), the mechanical properties of the composite beams have significant differences compared to those of the steel-normal concrete composite beams. To investigate the effect of reinforcement ratio on the force behavior of steel-UHPC composite beams, tests on the flexural performance of steel-UHPC composite beams with different reinforcement ratios under negative moments were carried out, and reasonable design of the composite beams was analyzed by using a numerical simulation method. In addition, the existing crack calculation methods for composite beams were validated. The results showed that the failure modes of the composite beams with different reinforcement ratios were similar. Increasing the reinforcement ratio from 2.01% to 2.98%, the ultimate capacity of the steel-UHPC composite beams was increased by 4% and the ultimate deflection was reduced by 7%, while the ductility was reduced by 11%. The cracking load was not enhanced, but the higher reinforcement ratio had a controlling effect on crack development and crack width in the late loading stage. For steel-UHPC composite beams, the appropriate reinforcement ratio should be less than 4%. Furthermore, the crack calculation formulas in the existing steel-concrete composite beam codes do not apply to steel-UHPC composite beams, and the calculation results were much smaller than the measured values. Among the related formulas for reinforced UHPC members, the calculated value of the formula in NF P 18–710 was closer to the measured value but the overall error was still large, so further research is needed. • Compares the flexural behavior of stee-UHPC composite beams under negativebending moment. • Analyzes the effect of reinforcement ratio on the development of cracks and the width of the main cracks. • Investigates the appropriate reinforcement ratio of steel-UHPC composite beams. • Investigates the variation in the contribution ratio of UHPC tensile strength during the loading process. • Compares and verifies the existing formulas for cracking of composite beams. [ABSTRACT FROM AUTHOR]

This paper conducted design and experimental study on frame specimen equipped with steel-HPEC (Hollow-core partially encased composite) spliced beams (SHS beam in short). SHS beams are comprised of two bare steel beams and an HPEC beam with thinner flange plates, present similar deformation and bearing capacity to traditional I-shaped steel structure, in addition to the benefits of good lateral stiffness and steel saving. Lateral low-cyclic loading tests were conducted on a bare steel frame and a frame with SHS beams to investigate their failure modes, seismic performance, and evaluate the feasibility of implementing SHS beams in frame structures. The frame specimen with SHS beams exhibited similar failure modes as those observed in steel frame specimen. Due to the higher stiffness of SHS beams, which effectively limited out-of-plane deformation in frame, SHS beam frame presented higher initial lateral stiffness, ultimate bearing capacity and energy dissipation capacity when contrast with bare steel frame. For calculations, SHS beams could be construed as stepped beams with variable rigidity. Finally, the calculation methods and formulas for initial lateral stiffness and ultimate bearing capacity of both the frames with SHS beams and bare steel frames were proposed, and the calculated results agreed well with the experimental values. • The SHS beam has reliable connections and similar deformation and bearing capacity to that of steel beam. • SHS beam has superior stiffness and effectively constrains out-of-plane deformation of frame structure. • The frame with SHS beams has higher stiffness, bearing capacity and energy dissipation. • The calculation methods of frame with SHS beams are simple and similar to that of bare steel frames. [ABSTRACT FROM AUTHOR]

Highlights • A review on torsional strengthening of RC beams with EB composites was provided. • A database of RC beams strengthened in torsion with EB FRP and FRCM was developed. • Data distribution, wrapping methods, failure modes, anchorage systems were evaluated. • The accuracy of existing analytical and numerical models was compared. • Design provisions for torsional strengthening with EB FRP composites were evaluated. Abstract The use of externally bonded (EB) fiber reinforced composites to strengthen reinforced concrete (RC) structures has been explored extensively in recent decades. While many studies have been conducted on the flexural, shear, and axial strengthening of RC members, far fewer studies have been conducted on torsional strengthening. Thus, the knowledge on the behavior of RC members strengthened in torsion with EB composites is rather limited. The aim of this paper was to present a comprehensive review and evaluation of torsional strengthening of RC beams using EB composites. A detailed survey of the literature was conducted, and a database of experimental tests was developed. The database includes beams reinforced with EB fiber reinforced polymer (FRP) and EB fiber reinforced cementitious matrix (FRCM) composites. The effectiveness of the strengthening system was examined in terms of geometrical and mechanical characteristics of the RC beam, composite type, and composite wrapping configuration. Different modes of failure of the strengthened beams were also discussed. Additionally, analytical and numerical methods developed to predict the torsional response of RC beams strengthened with EB composites were summarized and discussed. Finally, design provisions were examined based on the knowledge gained from this study. [ABSTRACT FROM AUTHOR]

The current research endeavours to evaluate the shear performance of the cold-formed steel (CFS) welded moment connection between beam-to-column with 36 laboratory tests. The web portions of the beam and column were connected by CFS welded clip-angle to form a CFS welded shear connection. Subsequently, it is converted into a welded moment connection by including a flange cleat between the flange portions. The shear capacity of the welded shear connection increases by an average of 67% after the inclusion of flange cleats, which is quantified using a performance ratio variable. This research presents two shear equations for the CFS welded moment connection (i) a new empirical shear equation; (ii) a new shear equation representing the shear strength of the moment connection as a function of the shear strength of the shear connection. The variability of the shear performance of welded moment and welded shear connections is expressed with force versus displacement plots and failure modes of the clip angles. The failure modes observed in the clip-angle in both welded moment and welded shear connections are (i) Local buckling and (ii) Distortional buckling. The shift in failure modes of some of the clip-angle in the WM connection (Local buckling) and the WS connection (Distortional buckling) indicates the effectiveness of flange-cleat in resisting due to free twisting of the beam because of load offset from the shear center. The design factors were also determined for the LRFD, LSD, and ASD methods by performing reliability studies. [Display omitted] • The shear capacity of moment connection with welded clip-angle and flange-cleat is experimentally evaluated. • The effectiveness of flange-cleat in improving the shear capacity of shear connection with welded clip-angle is quantified. • Along with empirical equation a new design approach was developed for the shear capacity of welded moment connection. • Comparative study was conducted between the shear and moment connections. • Reliability analysis was conducted and design factors were evaluated for the welded moment connection. [ABSTRACT FROM AUTHOR]

[Display omitted] • Different impact energies were selected based on the absorption energy of beams under static loading. • The difference in impact performance between reinforced concrete and reinforced concrete composite beams was tested. • The damage assessment method based on the residual deformation under impact loadings was proposed. • The impact performance of the reinforced concrete beams and reinforced concrete composite beams can be treated as the same within the tested impact loadings. Composite (CC) beams are employed more and more extensively because of their advantages in environmentally-friendly and rapid construction. These beams are possibly subjected to impact loadings due to occasional accidents or terrorist attacks during the service. It should be clarified whether the previous research achievements on the impact performance of reinforced concrete (RC) beams can be directly applied to CC beams. Five groups of full-scale CC beams and RC beams were fabricated with the same reinforcement ratios. One group of these specimens was tested under static bending loading, and the other eight specimens were tested under impact loading through the drop hammer test system. The failure modes, deformation, and force response of CC beams and RC beams were compared. The experimental results presented that the failure modes of CC beams are consistent with those of RC beams in the impact energy range of 1.0 E s ∼ 3.5 E s. The increasing impact energy changes the failure mode of CC beams from flexure failure to flexure‐shear failure until shear failure. With the increase of impact energy from 1.0 E s to 3.5 E s , the residual deformation increases first and then decreases, and the impact force of CC beams and RC beams are increased by 55.9% and 78.2%. There is little difference between CC beams and RC beams in peak deformation and residual deformation, a similar trend is found in impact force and support reaction force. Moreover, the beams can perform well impact resistance in the range of 1.0 E s ∼ 2.3 E s. Based on the residual deformation under impact loading and the deformation under static loading, the damage assessment method was proposed to evaluate the damage level of beams subjected to impact loadings. [ABSTRACT FROM AUTHOR]

• The influence of partial shear connection on the behaviour of the USCB with L-shaped shear connectors. • Three full-scale tests on the USCB with a degree of shear connection ranging from 0.4 to 1 under sagging bending moment. • A two-layer beam element formulation taking into account the interlayer slips in a co-rotational framework was also adapted. • A parametrical study is also carried out to investigate the effect of important parameters on the behaviour of the USCB. This paper presents a study on the influence of partial shear connection on the behaviour of the U-shaped steel concrete beams (USCB) with L-shaped shear connectors. An experimental campaign of three full-scale experimental tests on the USCB with a degree of shear connection ranging from 0.4 to 1 has been conducted under sagging bending moment. The test results showed high ductility of the USCB with both full and partial shear connections. The failure mode of the USCB was governed by the plastic buckling of the upper flanges of the U-shaped steel profile at the location of the shear connectors. The plastic moment resistance of the USCB with partial shear connection predicted by the full plastic analysis approach and by the simplified approach in Eurocode 4 agreed well with the experimental results. Furthermore, the flexural stiffness of the USCB with partial connections predicted by American and Australian standards fit well with the experimental results. A numerical model based on the two-layer beam element formulation taking into account the interlayer slips with continuous connection in a co-rotational framework was also adapted to determine the behaviour of the USCB. This model was validated against experimental tests as well as against the analytical approaches. It was finally used to carry out a parametrical study in order to investigate the effect of selected parameters such as the degree of shear connection, the concrete strength and the steel strength of U-shaped profile. [ABSTRACT FROM AUTHOR]

• A novel MPC based high performance concrete (HPC) was introduced into composite beam. • Four-point bending tests were performed on three composite beam specimens. • Effect of the parameters on the negative flexural behavior of specimens were compared and discussed. • A model for the shear stiffness of stud connector embedded in MPCHPC slabs was proposed. • The deflection and negative flexural capacity of specimens were calculated and analyzed. The main objective of this study was to evaluate the negative flexural behavior of steel- magnesium phosphate cement based high performance concrete (MPCHPC) composite beams by conducting four-point bending tests. Three composite beams were designed and tested by varying the longitudinal reinforcement ratio ρ l and MPCHPC strength. The failure modes, load–deflection behavior, elastic stiffness, flexural capacity, relative slip, strain distributions, crack development and crack width of specimens were investigated. The test results indicated that with the increase of ρ l , the initial stiffness and yield load of the specimens slightly increased and the crack width decreased, while the effects on the cracking load and ultimate flexural capacity were not significant. The MPCHPC strength had a greater effect on cracking load and early crack width, but had a minor effect on the initial stiffness, yield load, ultimate flexural capacity and the late-stage crack width of the specimens. Furthermore, the formula for evaluating the shear stiffness of stud connectors embedded in MPCHPC slabs was proposed based on previous push-out tests. Finally, the deflection and negative flexural capacity of steel-MPCHPC composite beams were calculated and analyzed by adopting existing codes and simplified plasticity models. [ABSTRACT FROM AUTHOR]

• The BFRP reinforced SWSSC beams composite stay-in-place formwork of TRE was proposed. • The composite beams after chloride salt dry-wet environment were studied. • Chloride salt dry-wet environment can improve the stiffness of BFRP reinforced SWSSC beam. • A method for predicting the bearing capacity of composite beams was proposed. In order to improve the serviceability performance and durability of basalt fiber-reinforced polymer (BFRP) reinforced seawater sea-sand concrete (SWSSC) beams in the marine environment, a composite of stay-in-place (SIP) form of textile-reinforced ECC (TRE) and BFRP reinforced seawater sea-sand concrete (BFRP-SWSSC) was designed, to enhance bearing capacity and deformation suppression ability of this composite structure in the marine environment. A total of 10 specimens with an effective span of 1500 mm and section size of 150 mm × 250 mm were designed in this experiment, including one BFRP-SWSSC beam and the rest composed of TRE composite as SIP forms. The effects of different dry-wet cycles, thicknesses of TRE SIP forms, shape of TRE SIP forms and production methods of TRE SIP forms on the bending performance of composite beams were studied. The specimens displayed as the TRE thickness increased, the failure mode changed from bending shear failure to balanced or compression failure. Whereas the bearing capacity of the specimens was indistinctively affected by 90∼270 dry-wet cycles. The deflection deformation and crack width of the beams were effectively improved by TRE SIP forms. Meanwhile the stiffness of composite beams was effectively improved by the chlorine salt dry-wet environment. With the effective bonding between TRE and SWSSC, the deflection and crack width of the composite beams were within specification limits. The eminent ductility of the composite beams was shown by the chlorine salt dry-wet environment, the ductility index of the specimen decreased with the dry-wet cycles increased from 90 to 270. Based on the section analysis method, a calculation method was proposed for the disabled bearing capacity of BFRP-SWSSC beams with U-shape TRE SIP forms in a normal environment. On this basis, the environmental impact factor of the salt dry-wet environment was suggested, and the experimental value is in commendable agreement with the theoretical value. [ABSTRACT FROM AUTHOR]

• The service limit of hybrid under-reinforced concrete beams was improved compared with that of FRP-RC beams. • The upper bound of the reinforcement ratio for hybrid-RC beams in the transition region was determined. • Hybrid under-reinforced concrete beams demonstrated better overall performance factors. • Existing design methods regarding flexural strength, deflection and crack widths were modified for hybrid under-reinforced concrete beams. This study aims to investigate the flexural behavior of hybrid reinforced concrete beams and study the design methods. Seven concrete beams reinforced with basalt fiber-reinforced polymer (BFRP) bars and steel bars, including six under-reinforced concrete beams and one slightly over-reinforced concrete beam, were constructed and subject to four-point loading. The reinforcement ratio was the main test parameter. The experimental results showed a transition region between the tension and compression failure modes. The upper bound of the reinforcement ratio of this region was determined through a statistical analysis of available data. The under-reinforced concrete beams with BFRP and steel bars yielded large deflections and crack widths, and the deformability factors of these beams were significantly larger than those of over-reinforced concrete beams with hybrid bars reported previously. The American Concrete Institute (ACI) method and Xue's equation were modified and employed to predict the flexural strength of under-reinforced concrete beams with hybrid bars. The experimental results were utilized to verify the accuracy of existing models to predict the pre-yielding and post-yielding deflections and assess the bond coefficients of the ribbed BFRP bars. [ABSTRACT FROM AUTHOR]

• Performance of U-shaped shear connectors in CFS-concrete composite beam is studied. • 10 full scale push-out tests are conducted to study the U-shaped shear connectors. • Four types of shear connectors were considered.· Two types of CFS beams with thickness of 1 and 2 mm are taken into account. • Ductility of the shear connectors is examined according to EC4 code. Since few studies have focused on the shear connectors in the composite cold-formed steel beams so far, this paper studies the behavior of the U-shaped shear connectors which can be used in the composite beams comprising cold-formed steel beam and concrete slab. Accordingly, ten full scale push-out tests were conducted to investigate the ultimate load, failure modes, ductility and stiffness of the U-shaped shear connectors. For this purpose, four types of shear connectors by different screw diameters and orientation of U-shaped shear connectors with respect to the direction of the load were considered; and utilized by two types of cold-formed steel beams with thickness of 1 and 2 mm. The results have shown that change of the screws' diameter from 4.8 to 6.3 mm, leads to an increase of the ultimate load about 25% and 40% for 1 mm and 2 mm thick specimens, respectively. It is also concluded that transverse shear connectors have a better performance than longitudinal ones considering both ultimate load and ductility. The main observed failure mode of all specimens was tilting and bearing in shear connectors except for two specimens which was incorporated with pull-over mode. Moreover, ductility of the shear connectors was examined according to EC4 code. The results show that except for two specimens, the other U-shaped shear connectors used in this study can be accounted ductile. [ABSTRACT FROM AUTHOR]

• MPC based high strength concrete (HSC) was first introduced into composite beam. • Experiments were performed on twenty-four push-out specimens. • Effect of the parameters on the shear behavior of headed stud connector were compared and discussed. • A model for the load-slip relationship of headed stud embedded in MPC based HSC was proposed. In this paper, magnesium phosphate cement (MPC) based high strength concrete (HSC) was first introduced into steel–concrete composite beams due to its better durability, good antirust performance, high early strength and eco-friendly. Twenty-four push-out specimens were conducted to examine the static behavior of headed stud connector in steel-MPC based HSC composite beams, including 21 MPC based concrete specimens and 3 normal concrete specimens. The failure modes, load-slip behavior, ductility, shear stiffness and shear capacity of stud connector were investigated. The effect of stud height, stud diameter, concrete strength and concrete type were also discussed. The test results showed that the shear behavior was greatly improved with the increase of the stud diameter. The aspect ratio, concrete strength and type had minor effect on the shear capacity of stud embedded in MPC based HSC concrete, while the shear stiffness and ductility were obviously affected. Furthermore, according to the existing equations and current design codes, the test results and calculated results of shear stiffness, load-slip behavior and shear capacity were compared and analyzed. Finally, an empirical equation considering stud diameter was put forward to assess the load-slip relationship of headed stud embedded in MPC based HSC. [ABSTRACT FROM AUTHOR]

• This study was performed to investigate of using the plug weld of an inaccessible end of CSCs on the failure modes and flexural behavior in SCSbeams contrast to one-end welded ones. • The specimens were numerically modeled and verified to investigate parameters including the thickness of the concrete, the number of rows of CSCs, the type of connection of the CSCs, faceplates thickness, concrete thickness, CSCs width and thickness on structural behavior of SCS beams. • Based on the relationships of reinforced concrete beams, a modification factor was proposed to predict the final strength of SCS beams. An important weakness of the steel–concrete-steel (SCS) sandwich structure with corrugated-strip shear connectors (CSCs) is the lack of access to make two-end welding of CSCs to the steel faceplates. In the present study, the use of plug weld was proposed to weld an inaccessible end of the CSCs. To evaluate the partial two-end welded CSCs, the SCS flexural beams including one specimen with one-end welded and four specimens with two-end welded were fabricated and tested under concentrated quasi-static loading. Then, failure modes and force–displacement diagrams were analyzed by examining parameters including the thickness of the concrete core, the number of the rows of CSCs and the type of connection of the CSCs (one-end or two-end welded). To further investigate, numerical model of the experimental specimens were created and validated. Using numerical models, the effect of parameters of steel faceplates thickness, concrete core thickness, CSCs breadth and thickness was investigated. The results showed that the use of partial two-end welded CSCs with plug welding, in addition to increasing the ultimate strength by about 30%, also provided more energy absorption than samples with one-end welded CSCs. Also, in most samples with two-end welded CSCs, the flexural failure mode was dominant over the shear failure. Finally, based on the relationships of reinforced concrete beams, a correction factor was proposed to predict the ultimate strength of the samples, which was in acceptable agreement with the experimental and numerical results. [ABSTRACT FROM AUTHOR]

• Electrical properties of mortars were tailored with carbon nanotubes (CNT) and carbon black (CB). • Saturation points were found to be 0.25% and 0.40% for CNT and CB, respectively. • Ambient-cured geopolymer composites had compressive strength more than 25 MPa. • Multifunctional large-scale reinforced geopolymer beams were achieved under shear and flexural failure mode. • CNT-based geopolymer beams were more responsive to change of strain compared to CB-based geopolymer beams. The investigation was performed on the self-sensing behavior of reinforced geopolymer concrete beams produced at ambient curing. Prior to investigation, carbon nanotubes (CNT) and carbon black (CB) were used in small-scale geopolymer specimens at different ratios and the electrical properties of the composites were tailored in the favor of self-sensing functionality. After characterization of mechanical and electrical properties, 150 × 150 × 750 mm3 (width × height × length) self-sensing reinforced geopolymer beams were produced with a span/effective depth ratio of 2.0. An experimental procedure was designed to obtain a mixed failure mode of shear and flexural. Engineering properties of large-scale beams were evaluated in terms of flexural strength, deflection capacities, initial stiffness and ductility ratios with the proposed design. Simultaneously, self-sensing assessments were performed continuously by the evaluation of relative factor in electrical resistivity of geopolymer beams at different loading levels. Microstructural and experimental results revealed that CNT-based beams significantly enhanced the load-carrying capacity and ductility that provided a high amount of energy dissipation capacity compared to CB-based beams. CNT-based beams exhibited 107.7%, 188.9%, 217% and 51% higher relative factor in electrical resistivity compared to CB-based beams at 25%, 50%, 75% and 100% of total applied load, respectively. Results indicate that applied load was continuously sensed by all geopolymer beams although CNT-based beams were more responsive to change of strain compared to CB-based beams at earlier stages of loading. [ABSTRACT FROM AUTHOR]

In this paper, the findings of numerical modeling of the composite action between normal concrete and Cold-Formed Steel (CFS) beams are presented. To obtain comprehensive structural behavior, the numerical model was designed using 3-D brick components. The simulation results were correlated to the experimental results of eight push tests, using three types of innovative shear connectors in addition to standard headed stud shear connectors, with two different thicknesses of a CFS channel beam. The proposed numerical model was found to be capable of simulating the failure mode of the push test as well as the behavior of shear connectors in order to provide composite action between the cold-formed steel beam and concrete using the concrete damaged plasticity model. [ABSTRACT FROM AUTHOR]

Composite beams comprised of steel sections and concrete slabs, are one of the most widely used beams due to their advantages such as improving stiffness and strength compared to bare steel or reinforced concrete beams. Moreover, another important advantage of such beams is to prevent buckling of steel section by placing it under tension, which is especially important for low-thickness steel sections such as cold-formed steel (CFS) sections. Although the use of CFS sections in combination with concrete slabs can increase the efficiency of such sections, their low thickness makes it difficult to weld traditional studs as shear connectors on their top flanges. The current paper presents an experimental investigation about the behavior of bolted shear connectors in the composite cold-formed steel beams as a suitable alternative to welded shear studs. To do so, three main parameters including thickness of CFS sections, and size and strength of bolts were taken into account. Fifteen full-scale push-out specimens were constructed and tested. The ultimate load, ductility, stiffness and failure mode of all specimens were then assessed; and their results were reported and precisely discussed. Based on the results, depending on the size and strength of bolts, the ultimate load per shear connector for 1 mm thick CFS sections' specimens is found between 6.2 and 8.6 KN, while this value for specimens by 2 mm thick CFS sections, is found between 15.6 and 26.8 KN. Moreover, based on EC4, the ductility of shear connectors was examined; the results indicate that all bolted shear connectors in this study can be assumed ductile and can be used in partial shear connections. • Structural performance of CFS-concrete composite beams is investigated. • 15 full scale push-out tests are conducted. • The failure modes, ductility and stiffness of the composite sections are studied. • Thickness of CFS sections, size and strength of bolts were taken into account. [ABSTRACT FROM AUTHOR]

[Display omitted] The negative bending behavior of the reinforcement stiffened cold-formed U-shaped steel and concrete composite beams (RCUCBs) is discussed in this paper. The negative bending experiment on 10 specimens were conducted and the damage process and corresponding static behavior in each stage are defined. Two distinct failure modes were found depending on whether the inverted U-shaped reinforcement (IUR) is installed or not: ductile plastic failure mode (when installed) and sudden elastic failure mode (when not installed). The IUR was observed to keep the integral action and improve the bending capacity and ductility of a RCUCB. The closed steel U-section stiffened by the reinforcement truss provides significant confinement to the encased concrete and even maintains its integrity after concrete cracking. The study results show that the plastic hinging of the framed RCUCB under vertical loads spreads to about L 0 /6 and suggest that the effective slab width in the negative moment zone is B e = L 0 /3 + b , similar to the positive moment case. Lastly, a negative bending design method was proposed, giving good calculations compared to the test results. The slab reinforcement, steel U-section, encased concrete, and bottom reinforcement contribute 53%, 30%, 11%, and 6% respectively to the negative bending capacity on average. [ABSTRACT FROM AUTHOR]

A timber–lightweight−concrete (TLC) composite beam connected with a ductile connector in which the ductile connector is made of a stainless−steel bolt anchored with nuts at both ends was proposed. The push−out results and bending performance of the TLC composite specimens were investigated by experimental testing. The push−out results of the shear specimens show that shear–slip curves exhibit good ductility and that their failure can be attributed to bolt buckling accompanied by lightweight concrete cracking. Through the bending tests of ten TLC composite beams and two contrast (pure timber) beams, the effects of different bolt diameters on the strengthening effect of the TLC composite beams were studied. The results show that the TLC composite beams and contrast timber beams break on the timber fiber at the lowest edge of the TLC composite beam, and the failure mode is attributed to bending failure, whereas the bolt connectors and lightweight concrete have no obvious breakage; moreover, the ductile bolt connectors show a good connection performance until the TLC composite beams fail. The ultimate bearing capacities of the TLC composite beams increase 2.03–3.5 times compared to those of the contrast beams, while the mid-span maximum deformation decrease nearly doubled. [ABSTRACT FROM AUTHOR]

• A new type of BFRP-SWSSC beam with TRE tension zone cover was proposed. • Effects of various factors were revealed (such as number of textile layers). • The composite layer can promote the serviceability and ductility of the beam. • A method for predicting the bearing capacity of composite beams was proposed. To improve the service behavior of basalt fiber reinforced polymer (BFRP) reinforced seawater sea-sand concrete (BFRP-SWSSC) beams, textile reinforced ECC (TRE) are utilized in the tensile zone to replace the traditional SWSSC. The experimental parameters of TRE included the number of textile layers, the matrix thickness, and the matrix type. The results showed that the failure mode of the composite beams transitioned from tensile failure to balanced failure with the increase in the matrix thickness and the number of textile layers. The composite layer can promote the ultimate capacity to some extent. Compared with engineered cementitious composites (ECC) and textile reinforced concrete (TRC), TRE can more effectively reduce the deflection and crack width, as well as improve the ductility, at the service stage. The improvement was more significant when the matrix thickness and the number of textile layers increased. Compared with those of the control beams, the deflection and crack width were reduced by 63.2% and 71.3% under the service loads, respectively, while the ductility index was improved by 29.1% for the TRE composite beam with three textile layers. Furthermore, the formulas for the ultimate capacity of the composite beams were developed and verified by the experiments. [ABSTRACT FROM AUTHOR]

• The bearing capacity of LAC-CC composite beams can be designed according to the plane-section assumption. • The cracking moment formula applicable to LAC-CC composite beams was proposed. • The applicability of the method for calculating the ultimate bearing capacity of conventional concrete beams in GB50010-2010 was verified. • The formulas for average crack spacing and average crack width were derived. This study explores the flexural behavior of precast, prestressed, lightweight aggregate concrete-conventional concrete composite beams. Ten specimens were tested with consideration of the height of the combined interface, the reinforcement ratio, and the location of the lightweight-aggregate concrete. Failure modes, bearing capacities, deformation characteristics, and crack widths were observed, and the influences of various parameters on flexural performance are discussed. The results show that the bending process of lightweight aggregate concrete-conventional concrete composite beams is similar to that of conventional concrete beams. There is no slip failure at the combined interface, the flexural capacity of a lightweight aggregate concrete-conventional concrete composite beam can be calculated based on the plane-section assumption. Considering the proportion of lightweight-aggregate concrete in the lightweight aggregate concrete-conventional concrete composite beam and combined with the cracking moment calculation formula in GB50010-2010, a cracking moment formula applicable to lightweight aggregate concrete-conventional concrete composite beams is proposed. The applicability of the method for calculating the ultimate bearing capacity of conventional concrete beams in GB50010-2010 is verified. Based on regression analysis of test data and the introduction of a comprehensive coefficient of influence C m , formulas for average crack spacing and average crack width are derived, which lays a theoretical foundation for further engineering applications. [ABSTRACT FROM AUTHOR]

• Shear in monolithic and composite concrete beams without stirrups was studied. • Slab width, interface, concrete strength and differential shrinkage were analysed. • The interface between concretes modified the critical shear crack direction. • The slab contributed to increase the shear strength of the composite specimen. • An over-strength of the T-shaped composite beams due to arching action was noted. Composite concrete members without web reinforcement are often used in precast construction. The contribution of the cast-in-place concrete topping slab to vertical shear strength has been traditionally disregarded. However, significant cost savings can result from designing and assessing these structures if this contribution is considered. This paper presents the experimental study of a series of 21 monolithic and composite (precast beam and cast-in-place slab) specimens without web reinforcement, and with rectangular and T-shaped cross-sections, failing in shear. The vertical shear strength was analysed by the following test variables: cross-section shape, the existence of an interface between different aged concretes, strengths of the two concretes and the differential shrinkage effect. From these experimental tests, it was concluded that the slab contributed to shear strength, the use of high-strength concrete slightly increased specimens' shear strength and the differential shrinkage did not reduce shear strength. Specimens' failure modes were analysed based on their shear transfer mechanisms, noticing that the arching action in the slab was considerable after critical shear crack formation. The vertical shear strength experimental results were well predicted by the codes' formulations (Eurocode 2, Model Code 2010 and ACI 318-19) when composite beam depth was taken for the calculations instead of beam depth. Codes significantly underestimated the horizontal shear strengths of the composite specimens. [ABSTRACT FROM AUTHOR]

This paper investigated the static behaviour of glass fibre reinforced polymer (GFRP) built-up hollow and concrete filled built-up beams tested under four-point bending with a span-to-depth ratio of 1.67, therefore focusing their shear performance. Two parameters considered for hollow sections were longitudinal web stiffener and strengthening at the web–flange junction. The experimental results indicated that the GFRP hollow beams failed by web crushing at supports; therefore, the longitudinal web stiffener has an insignificant effect on improving the maximum load. Strengthening web–flange junctions using rectangular hollow sections increased the maximum load by 47%. Concrete infill could effectively prevent the web crushing, and it demonstrated the highest load increment of 162%. The concrete filled GFRP composite beam failed by diagonal tension in the lightweight concrete core. The finite element models adopting Hashin damage criteria yielded are in good agreement with the experimental results in terms of maximum load and failure mode. Based on the numerical study, the longitudinal web stiffener could prevent the web buckling of the slender GFRP beam and improved the maximum load by 136%. The maximum load may be further improved by increasing the thickness of the GFRP section and the size of rectangular hollow sections used for strengthening. It was found that the bond–slip at the concrete–GFRP interface affected the shear resistance of concrete–GFRP composite beam. [ABSTRACT FROM AUTHOR]

• Corrosion resistance of SCC and LWSCC beams covered or wrapped with ECC. • Corrosion performance based on current flow, half-cell potential and rebar mass loss. • Shear resistance, ductility and energy absorption capacity of corroded ECC wrapped beams. • Comparative post-corrosion structural performance of SCC and LWSCC beams. • Comparative structural performance of un-corroded and corroded beams. In this study, effect of Engineered Cementitious Composite (ECC) covering and wrapping on corrosion resistance and structural performance of un-corroded and corroded shear beams made of self-consolidating concrete (SCC) and light weight SCC (LWSCC) has been extensively investigated. An accelerated corrosion test on beams has been performed to reach the required high degrees of corrosion (30–40% of rebar mass loss). Both corrosion and structural performance of corroded beams has been assessed and analysed. The structural performance of un-corroded and corroded beams has also been compared. The corrosion performance has been evaluated in terms of current flow, half cell potential, actual rebar mass loss, reduction in diameter etc. The structural performance has been assessed and compared in terms of load–deflection behaviour, 1st flexure/diagonal cracking load, ultimate failure load, post cracking shear resistance, ductility and energy absorption capacity, failure load and failure modes. Composite beams with ECC covering exhibited superior corrosion resistance and post-corrosion structural performance as compared to full depth SCC or LWSCC counterparts. The performance of ECC wrapped composite beams has been found to be better than those with covering. Overall, ECC can be used as covering or wrapping in conventional SCC/LWSCC beams to enhance their corrosion resistance performance significantly. [ABSTRACT FROM AUTHOR]