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The timber board interlayer is applied as the formwork for the pouring of concrete slab in various practical applications of timber–concrete composite structures, with the rehabilitation of timber buildings, in particular. At present, there are few studies performed to study the shear stiffness of inclined screws in timber–concrete composite beams with timber board interlayer. In this article, eight groups of shear tests were carried out to study the shear stiffness of inclined screws in timber–concrete composite beams with timber board interlayer. The key parameters included the embedment depth of the screw connector into timber, screw diameter, the thickness of concrete slab, and concrete strength. As indicated by the test results, the shear stiffness of the inclined screws was improved as the embedment depth of screw into timber and screw diameter increased. When the embedded depth of screw into concrete remained unchanged, the thickness of concrete slab and concrete strength exhibited no significant impact on the shear stiffness of inclined crossing screws. On the basis of the theory of a beam on a two-dimensional elastic foundation, the calculation method for predicting the shear stiffness of inclined screw in timber–concrete composite beams with interlayer was proposed. The comparisons demonstrated that the shear stiffness of inclined screw can be well predicted using the calculation method.

Ductile shear connectors are often applied in timber-concrete composite beams. The relative interface slip of such kind of composite beams will affect the mechanical performance of the composite beams and result in structural nonlinearity. Gamma method which adopts effective bending stiffness to reflect semi-rigid connection is recommended in Eurocode 5. The effective bending stiffness is irrelevant to external loads and calculation points of the composite beam. However, actual bending stiffness distribution along the beam is variable due to that shear connectors are subjected to different shear force. In order to verify the accuracy of gamma method, four-point bending tests of a total of three glulam-concrete composite beams with lag screw connectors and one pure glulam beam were conducted in this article. The failure mode, bearing capacity, and load–deflection relationship were investigated in the experiment. Meanwhile, push-out tests of composite beams were also conducted for determination of the force–displacement relationship of ductile shear connectors. Then, numerical simulation using beam-truss model was established for investigation on the mechanism of composite beams. Finally, theoretical analysis of composite beams considering the effect of interface slip was also presented. Comparing results from gamma method with the presented method, it is shown that both methods can calculate deflection at serviceability limit state with high precision. However, non-uniform distribution of actual bending stiffness cannot be reflected by gamma method.

Concrete-filled fiber-reinforced polymer tubes are a novel form of composite columns, which are particularly attractive for structural members in harsh environments and seismic regions due to their corrosion resistance and ductile behavior. Over the past two decades, many studies have been conducted on concrete-filled fiber-reinforced polymer tubes under axial compression, and many stress–strain models have been proposed. However, existing studies mainly focused on concrete-filled fiber-reinforced polymer tubes with only hoop fibers. In order to investigate the effect of fiber angles (i.e. the fiber angle between the fiber orientation and the longitudinal axis of fiber-reinforced polymer tube), this study conducted axial compression tests of 42 concrete-filled fiber-reinforced polymer tubes with ±80°, ±60°, or ±45° fiber angles. These concrete-filled fiber-reinforced polymer tubes were constructed using normal-strength concrete or high-strength concrete. Fiber-reinforced polymer tube thickness was also investigated as an important parameter. In order to clarify the effect of fiber angles on the properties of fiber-reinforced polymer tubes, axial compression tests on 15 short fiber-reinforced polymer tubes and tensile split-disk tests on 75 fiber-reinforced polymer rings were conducted. Experimental results indicate that fiber angles had significant influences on the hoop properties of fiber-reinforced polymer tube; the confinement effect of fiber-reinforced polymer tube and the peak stress of the confined concrete decreased with the decrease of the absolute value of fiber angles, while the ultimate strain of the confined concrete increased with the decrease of the absolute value of fiber angles. Two existing stress–strain models, which were developed mainly on test results of concrete confined by fiber-reinforced polymer tubes with only hoop fibers, are capable of providing reasonably accurate predictions for concrete-filled fiber-reinforced polymer tubes with ±80° and ±60° fiber angles, but it underestimates the ultimate axial strain of concrete-filled fiber-reinforced polymer tubes with ±45° fiber angles.

The mechanical performance of shear connectors has an important effect on the load bearing capacity and the bending stiffness of timer-concrete composite (TCC) beams. Most studies reported so far have focused on the shear behavior of the single inclined screw working only under shear–tension stress. However, there are few researches on the shear behavior of inclined cross screws. In this paper, a total of thirty-six push-out tests were conducted to investigate the shear behavior of the inclined cross lag screws for glulam-concrete composite beams. Based on the push-out test results, the influences of concrete strength, screw diameter, penetration length of screw into timber, screw inclination angle and screw arrangement with respect to the shear plane on the shear bearing capacity and slip modulus were investigated in detail. Two types of failure mechanisms of inclined cross lag screws were observed from the push-out tests: cone expulsion of concrete ahead of the shear-compression loaded screw and the shear-tensile loaded screw withdrawn from timber. When the inclined screws worked only under shear-compression load, the screw connectors were in the worst stress state. Since the direction of interface shear force in timber-concrete composite beams changed constantly under seismic load, the optimal screw arrangement was the crossed screws working simultaneously under shear-compression and shear–tension load. In addition, the analytical models were proposed to predict the shear bearing capacity and slip modulus of the inclined cross screws, and the calculated results were in good agreement with the test results.

Recently, perfobond connectors for steel-concrete composite structures have received extensive research attention due to their excellent bonding and fatigue performance, and the construction convenience. However, the research on the long-term behavior of perfobond connectors was seldom reported. This paper presents the results of laboratory tests on perfobond connectors, including twenty short-term specimens and six long-term specimens. Parametric study was conducted to investigate the influence of the hole diameter in the connector, the number of the holes, the thickness of the connector, the concrete strength as well as the diameter of the transverse rebar on the shear performance of perfobond connectors. For the short-term test series, the failure modes of the connector, the load-slip response, the ultimate shear bearing capacity and the load-strain curves of transverse rebar were studied. For the long-term test series, the transverse rebar strain, the relative slip between the steel beam and the concrete slab and the stress around the holes with duration of loading were discussed. The shear performance of perfobond connectors after long-term loading was also investigated. Finally, based on the test data from both this paper and open literature, a model was proposed to predict the shear bearing capacity of perfobond connectors.

A novel method for nonlinear parameter identification of partially composite beams using long-gauge strain responses is proposed in this paper. Firstly, theoretical analysis shows that neutral axis position of timber beam and concrete slab can be estimated by measured long-gauge strain and material properties. Then, distribution of curvature, bending stiffness, deflection and interface slip can be determined by identified neutral axis position. Secondly, timber-concrete composite beams connected by ductile connectors with different degree of composite action are designed to verify the presented method. Experimental results show that the estimated parameters (neutral axis position, bending stiffness and interface slip) can clearly reflect and quantify the deterioration process of partially composite beams. Meanwhile, both global and local responses can be predicted by long-gauge strain sensors. The predicted responses (deflection at mid-span and strain along the beam height) agree well with the test results when partially composite action is considered, the errors will be unacceptable without considering partially composite action. Hence, the presented method can be utilized for better understanding of mechanical properties of partially composite beams and performance assessment of existing composite structures.

Quantitative assessment of strengthened concrete structures using self-sensing fiber-reinforced polymer sheets is presented in this article. First, strain distribution along the height of a structure induced by pre-tension force (initiate state) is theoretically estimated. Second, the procedure for parameter estimation of prestressed fiber-reinforced polymer–strengthened structures under external load using measured and pre-tension force–induced strain is established, and nonlinearity caused by random cracks is considered in the method. Both local parameters (neutral axis position, bending stiffness distribution, strain distribution along the cross section, etc.) and global parameter (deflection) of structures can be accurately estimated by measured long-gauge strain responses. Finally, both prestressed fiber–reinforced polymer–strengthened and reinforced concrete beams installed with long-gauge fiber Bragg grating sensors have been experimentally investigated to prove the effectiveness of this method. Experimental results indicate that the estimated neutral axis height and local bending stiffness can reflect initiation of random cracks and deterioration process of structures under increasing external load. Meanwhile, the estimated strain along the beam height and deflection at mid-span agree well with the measured ones, which further verifies the accuracy of the estimated neutral axis position affected by randomly appeared cracks. Hence, the method can be utilized for assessment and maintenance of fiber-reinforced polymer–strengthened structures.

Mechanical behavior of the shear connections has a significant influence on both the load-carrying capacity and the bending stiffness of timber-concrete composite (TCC) beams. All the studies reported so far have concentrated on the performance of TCC connections in mature concrete. The performance of shear connections for TCC beams at early concrete ages, however, has not been investigated yet. This information is essential to evaluate the structural behavior of TCC floors or bridges during construction. In this paper, a total of 18 push-out tests with concrete ages ranging from 12 h to 28 days are performed, to investigate the early-age performance of lag screw shear connections in the lightweight concrete. Development of concrete strength with time is also analyzed. At the concrete ages shorter than 7 days, both the stiffness and strength of the screw connectors increase evidently with time, which follows the same growth trend with the concrete strength. After a 7-day cure, screw shear connections reach almost 100% of both the 28-day serviceability slip modulus and shear strength. Material properties of the glulam and the screw fastener are decisive in the shear performance of connections when the concrete hardens to some degree. Based on the experimental results, the accuracy of the design methods proposed in Eurocode 5 is evaluated. In addition, by non-linear regression of the experiment data, expressions to predict the development of load-carrying capacity and serviceability slip modulus for screw shear connections before 28 days are established.

Hybrid FRP-concrete-steel double-skin tubular columns (hybrid DSTCs) are novel hollow columns consisting of an outer FRP tube, an inner steel tube, and the concrete between the two tubes. Hybrid DSTCs possess important advantages, such as excellent corrosion resistance as well as remarkable seismic resistance. However, existing studies are mainly focused on hybrid DSTCs with a circular cross section or a square cross section. When a column is subjected to different load levels in the two horizontal directions, a rectangular column is preferred as it can provide different bending stiffness and moment capacity around its two axes of symmetry. This paper presents an experimental study on rectangular DSTCs with a particular focus on the effect of the cross-sectional aspect ratio (i.e., the ratio of the breadth to the width of the rectangular cross section). The effect of the cross-sectional shape of the inner steel tube (i.e., both elliptical and rectangular inner steel tubes were used) and the effect of FRP tube thickness were also investigated experimentally. Experimental results show that a larger aspect ratio will have no negative effect on the confinement effect in rectangular DSTCs; a rectangular DSTC with a larger aspect ratio generally has a larger ultimate axial strain and a higher axial stress at the ultimate axial strain; rectangular DSTCs with an elliptical steel tube generally have better performance than corresponding specimens with a rectangular steel tube. An existing model, which was developed based on a model for rectangular FRP-confined concrete columns and a model for circular DSTCs, is verified using the test results of the present study. The model generally provides close predictions for the peak axial stress of the confined concrete but yields conservative predictions for the ultimate axial strain for rectangular DSTCs.

In various practical applications of timber-concrete composite (TCC) beams, particularly for the rehabilitation of timber buildings, there is a timber board interlayer at the interface. The timber board is applied as the formwork for the pouring of concrete slab and usually left behind as part of the composite structure. There are few investigations performed on the mechanical behaviour of TCC beams with timber board interlayer. In this paper, two full-scale glulam-concrete composite beams with inclined crossing screws and notched connectors were constructed and loaded by four-point bending to investigate the flexural performance of composite beams with timber board interlayer. Experimental results demonstrated that the failure mechanism of the composite beam was combined bending and tensile failure of the glulam beam. Due to the flexibility of the shear connector, relative slip occurred at the interface and the assumption of a plane section remaining plane did not hold for the composite cross-section as a unit. Additionally, analytical models for the bending stiffness and load-bearing capacity of TCC beams with interlayer were proposed. Comparisons demonstrated that the bending capacity and stiffness of TCC beams with interlayer could be well predicted using the calculation method.

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.

In order to investigate the mechanical behavior of the partially concrete encased composite beam under hogging moment, static loading tests were conducted on one conventional composite beam and three partially concrete encased composite beams. The results show that partially concrete encased composite beams have higher stiffness and flexural capacity under hogging moment as compared with conventional composite beams. It is also found that the concrete encasement is able to enhance the local bucking resistance of the steel beam and effectively reduces the propagation speed of crack width under hogging moment. By comparing different partially concrete encased composite beams, it is indicated that the stiffness and flexural capacity of partially concrete encased composite beams increase with the increase in reinforcement ratio of the concrete slab. Also, with the increase in the reinforcement ratio of the concrete slab, the distribution of cracks on the slab is denser and the propagation speed of crack width reduces. In addition, the calculation methods in both European code and Chinese code can well predict the crack width on the concrete slab, and the ultimate flexural capacity predicted from the simplified plastic theory in Eurocode 4 is in good agreement with test results.

The design of timber-concrete composite (TCC) floors is usually subject to the requirement of serviceability rather than strength. Most studies reported so far focus on the dynamic characteristics of the TCC floor. However, there are few studies conducted on the vibration comfort of TCC floors under human-induced excitation. In this paper, dynamic experiments were performed to obtain the fundamental frequency and the damping ratio of a glulam-concrete composite floor under simply supported and fixed support boundary conditions, respectively. Besides, an in-depth investigation was carried out considering the influences of walking path, step frequency, number of pedestrians, arrangement of walking loads and walking mode on the vibration response of the composite floor. Test results showed that the peak acceleration of the floor increased with an increase in step frequency and the number of pedestrians. Regular walking caused a higher peak acceleration compared to irregular walking. At the same step frequency, marking time caused a larger peak acceleration than normal walking. Three existing analytical models were applied to predict the fundamental frequency of the floor, which conformed to the experimental results. In addition, a calculation model and finite element (FE) models were proposed to predict the peak floor acceleration under a single person walking, and the numerical model results agree well with the test results. A double-index was proposed to evaluate the vibration serviceability of TCC floors; the fundamental frequency of the floor is required to exceed 15 Hz and the peak acceleration ought to be less than 0.15 m/s2.

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.

At present, the impact sound insulation performance of the residential floor attracts increasing attention, which is a critical index to evaluate the physical performance of the residential building. Improving the sound insulation performance is an effective measure to improve the living quality and solve the contradictions between neighbors. Therefore, many sound insulation standards have been established to guide the design of building sound insulation. In this paper, comparisons between Chinese code and Eurocode on the impact sound insulation requirements of the residential floor were presented, including the evaluation parameter and the limit value of sound insulation. In addition, the applicability of limit value of sound insulation standard for each country was analyzed in detail through the existing experimental data of different floor structures, and then reasonable suggestions were put forward.

The mechanical behavior and the law of moment redistribution of the partially encased continuous composite beam (PECCB) are investigated in this paper. One common continuous composite beam and three PECCBs were tested. The main variable parameter of the three PECCB specimens is the amount of longitudinal reinforcement in the concrete slab of hogging moment region. Owing to the contribution of the web encasement, PECCBs have much slower crack propagation speed in the hogging moment region and higher ultimate capacity. The web encasement also contributes to postponing the yielding of the bottom flange, and therefore prevents local buckling in the steel girder. As the amount of reinforcement in the concrete slab of hogging moment region increases, the degree of moment redistribution of PECCBs decreases. On the basis of analyzing the moment redistribution requirement for plastic design and the ultimate rotation capacity of hogging moment section, the required and available moment redistribution factors of PECCBs are obtained. A parameter Rp is introduced to evaluate the relative relationship between the longitudinal reinforcement in the concrete slab and the rest part of the partially encased section, and the value of Rp should be restricted within 0.35 to enable full moment redistribution for plastic design of PECCBs.

This paper presents an experimental investigation of bending performance of composite sandwich panels with new mixed core, sandwich panels were tested by four-point bending test. Parametric study was conducted to investigate the influence of different core materials on the failure mode, ultimate bearing capacity, stiffness and ductility of composite sandwich panels. The results of the experimental investigation showed that the mixed core can change the failure mode of sandwich panels. The failure mode of wooden panels is characterized by tensile failure of bottom wood, and the failure mode of composite sandwich panels with wood core is that the surface layer and core are stripped and the webs are damaged by shear, while the failure mode of composite sandwich panels with wood and polyurethane foam mixed core is the shear failure of the web. Composite sandwich panels with GFRP-wood-polyurethane foam core have better bending performance and can effectively reduce the weight of panels.