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In this study, the structural performance of a new type of lightweight composite cold-formed steel and timber (CFST) flooring system has been investigated by conducting four-point bending tests on 13 specimens. A bare cold-formed steel system without timber sheathing was also tested to provide a benchmark response to which the strength and stiffness of the composite system were compared. This paper presents key findings on the flooring system's structural behavior and performance parameters, such as ultimate bending capacity, load-deflection response, load-slip response, and failure modes, by categorizing 13 specimens into four subgroups based on shear connector types and spacings. In the proposed composite CFST flooring system, 45-mm thick structural plywood panels were connected to the 2.4-mm thick cold-formed steel C-section joist using self-drilling screws, coach screws, and nuts and bolts. The performance of different types of shear connectors on the composite action is experimentally investigated and compared with the theoretical plastic section. Furthermore, the load-carrying capacity, effective bending stiffness, and deflection of composite CFST beams were computed theoretically using elastic theory and compared to experimental results, which showed good agreement. [ABSTRACT FROM AUTHOR]

In this study, the flexural behavior of noncompact and slender concrete-filled U-section (CFU) beams was investigated focusing on local buckling of U-section walls and shear transfer across the beam-to-slab interface. Seven large-scale CFU beam specimens were tested under negative bending. The width-to-thickness ratios of U-section walls (i.e., flanges and webs) and stiffening details for preventing local buckling were considered as the test variables. The tests showed that, due to excessive slab reinforcement, all specimens were failed by shear failure at the composite interface of beam and slab after flexural yielding. The ultimate strength and deformation capacity of CFU beams were degraded by flange and web local buckling. Buckling modes of U-section walls were affected by the stiffening details. The ultimate strengths of noncompact and slender CFU beams were compared with the nominal strengths calculated in accordance current standards. In addition, the flexural behavior of CFU beams affected by the local buckling and partial debonding of U-section walls and slip behavior at the composite interface was further investigated through fiber-based section analyses based on the effective stress–strain models of materials. [ABSTRACT FROM AUTHOR]

In order to explore the flexural performance of high-strength steel (HSS)/ultrahigh performance concrete (UHPC) composite beams, a total of six HSS-UHPC composite beams with varying levels of interfacial shear connectivity, arrangements of perfobond strip connectors (PBL), and variable thicknesses of concrete decks were fabricated and tested. The failure mode, flexural stiffness, load-deflection curve, strain history, and interfacial slippages obtained from the composite beams are presented and discussed. Experimental results indicated that despite the lightweight feature of such a hybrid system, the HSS-UHPC composite beams exhibited high flexural stiffness and favorable ductility. As the level of shear connectivity decreases, the bending resistance of HSS-UHPC composite beams decreases, while the beams' ductility exhibits slight enhancement. The PBL arrangement has crucial effects on the behavior of HSS-UHPC composite beams, and the beams' ductility was improved by approximately 48.9% by alternating uniformly distributed PBLs to a nonuniform distribution pattern. Experimental results also highlighted the influence of the UHPC deck thickness on the flexural performance of the composite beams. As compared to an 80.0 mm-thick UHPC deck, the 100.0 mm-thick UHPC deck witnessed increases in bending stiffness, yield moment, and ultimate resistance of the composite beam by 19.8%, 22.8%, and 14.6%, respectively. Comparisons between the results obtained from the tests and analytical procedures for predicting HSS-UHPC composite beams resistances were performed to assess the feasibility of existing design approaches. Results of the study confirmed that equations recommended by GB 50017-2017 have favorable accuracy in calculating the bending resistance of HSS-UHPC composite beams with uniformly distributed PBLs, while for HSS-UHPC composite beams with nonuniformly distributed PBLs, both the AASHTO LRFD and Ban et al. equations are recommended. [ABSTRACT FROM AUTHOR]

In this paper, a displacement-based weak-form quadrature element (WQE) is formulated and implemented for long-term response analysis of steel–concrete composite beams. The effects of creep and shrinkage taking place in reinforced concrete slabs are considered by using an integral type viscoelastic model. Timoshenko and Kant higher-order beam theories are applied to depict the reinforced concrete slab and steel beam, respectively, so as to achieve accuracy close to that of the 3D shell model, but at a much lower computational cost. The proposed model and program are verified through comparisons with the 3D shell and classical beam models. To investigate the improvement of convergence performance contributed by the differential quadrature technique, detailed comparisons are made between the WQE and conventional finite element. Numerical results show that the composite beams modeled with the Timoshenko-Kant kinematical assumption can achieve accuracy close to that of the 3D shell model; due to the ability to conveniently adjust interpolation order, the proposed WQE acquires much higher computational efficiency than the conventional finite element; the severe numerical smoothness problem common in the displacement-based finite element model (FEM) is significantly alleviated by the higher-order WQE method. [ABSTRACT FROM AUTHOR]

This work presents a collocation method for study of the static behavior of composite beams with consideration of linear and nonlinear partial interactions. The collocation concept is first introduced; the internal global trial functions for the displacement field are then assumed in terms of Fourier series expansion representations. In order to obtain the unknown coefficients, several collocation points, distributed uniformly along the span of a composite beam, are adopted to set up the systems of equations by satisfying governing equations and boundary conditions. Both single- and multispan composite beams are investigated and validated against other analytical and numerical methods, where good agreement is always obtained. The efficiency of the collocation technique is then tested with different numbers of collocation points or harmonic terms to generate converged results. The collocation technique is also applied to the nonlinear analysis of partial-interaction composite beams. The theoretical distinctions between the present technique and other methods are finally explained. [ABSTRACT FROM AUTHOR]

Composite timber beams strengthened by U-shape steel sections and carbon fiber-reinforced plastic (CFRP) are studied experimentally in this paper. Specimens with various strengthening, i.e., steel only, CFRP only, and a combination of the two, were considered under three-point flexural tests. Failure, displacement and strain response, ductility, bending capacity, and structural efficiency were evaluated for the present tested models. Dramatic enhancement of the capacity in addition to improved deflection and ductility were gained for the strengthened beams relative to the plain specimens, indicating the effectiveness of the reinforcement on the flexural strength of such composite beams. [ABSTRACT FROM AUTHOR]

The stiffness and strength of a composite structure formed by a slab and an underlying beam made of different materials strongly depends on the shear coupling at their interface, which in general is not perfect because of the compliance of the shear connectors. The proposed approach interprets the effects of this partial interaction by establishing an equivalence, in terms of stress and deflection, with a composite beam with perfect shear bonding, but with a slab of smaller effective width. The method relies upon the minimization of the strain energy functional within a restricted class of shape functions for the deformation, finding the best approximation intermediate between the two limit cases of frictionless sliding and perfect shear coupling. If the response of the connectors is linear elastic, a simple formula is reached to calculate the effective width of the slab as a function of the static scheme and of the mechanical and geometrical properties. If the response is nonlinear, as it is in practice, the effective width is found by solving an algebraic equation, whose coefficients also depend on the magnitude of the applied load. Comparisons with numerical experiments confirm the very good accuracy of the proposed approach. [ABSTRACT FROM AUTHOR]

The present study complements recent published work by developing a general closed-form solution for the analysis of steel beams reinforced with glass-fiber-reinforced plastic (GFRP) plates under general loading and boundary conditions. Comparisons against three-dimensional (3D) finite-element (FE) solutions indicate that the solution accurately captures the transverse-longitudinal and predominantly lateral responses. For predominantly torsional responses, the solution is shown to provide good predictions when the shear modulus of the adhesive layer is weak. For cases where the shear modulus is stiff, the present theory is found to lead to an overly stiff response. Careful examination of strain profiles as predicted by the 3D FE analyses provides valuable insight on the reason for the overly stiff behavior in such cases and shows the necessity of incorporating transverse shear deformation effects into the formulation. [ABSTRACT FROM AUTHOR]

Posttensioning has been used successfully to improve the performance of existing bridge structures. High-strength tendons can be used to effectively increase the ultimate capacity of composite beams. The main purpose of this paper is to develop a reliable three-dimensional (3D) finite-element (FE) model to simulate the nonlinear flexural behavior of steel-concrete composite beams strengthened with externally posttensioned tendons. A 3D FE model was used, where the nonlinear material behavior and geometrical analysis based on incremental-iterative load methods were adopted. The effective posttensioning stress was applied as initial strain in the link element used to model the tendons. To verify the accuracy of the developed 3D FE model, comparison between the FE analysis results and previous experimental results is presented. In-depth study has been carried out on the overall behavior of the strengthened beam and the effect of external posttensioning on stiffness, induced stresses, slippage between concrete slab and steel beam, and shear connector moments. The results of the FE model compared well with the experimental results and the FE analysis. Using external posttensioning tendons in the positive moment region for steel-concrete composite beams increased their ultimate capacity by 25%, the stiffness by 33%, and significantly improved the overall response of the bridge structural system. [ABSTRACT FROM AUTHOR]

Although concrete in compression and wood in flexural tension are both intrinsically brittle, composite beams made of these two materials can develop a reliable measure of softening before failure when ductile shear connectors are used to link concrete and wood, provided the connectors are dimensioned to yield before failure of wood or concrete. This article describes an analytical method for predicting the complete load-deflection response of timber/concrete composite beams with ductile shear connectors. The approach involves the superposition of results obtained from a series of linear models, each of which has a progressively smaller number of connectors corresponding to the order in which they yield. The nonlinear behavior of the system can thus be determined without iteration using only linear computations. The analytical method is validated against experimental data. [ABSTRACT FROM AUTHOR]

Composite beams comprised of concrete slabs and steel beams joined by mechanical shear connectors are commonly used in modern building design. The use of innovative deconstructable high-strength friction-grip bolt (HSFGB) shear connectors and reduced-emissions precast geopolymer concrete slabs in composite beam design can greatly enhance the sustainability of building infrastructure. Hitherto, research contributions that address the behavior of composite beams with HSFGB shear connectors and precast geopolymer concrete slabs are very limited. To provide a contribution to this area of research, an effective finite element model of push-out testing is developed to investigate the ultimate strength and the load-slip characteristics of shear connection using HSFGB connectors and geopolymer concrete slabs in this proposed sustainable composite beam application. The accuracy of the proposed finite element model is validated by comparing its predictions with experimental results on push-out test specimens also reported in the paper. The effects of the change in the bolt pretension, its clearance between the hole in the steel flange, its diameter and tensile strength, and the compressive strength of the geopolymer concrete are elucidated through parametric studies. Practical design recommendations in algebraic form are proposed and verified for predicting the ultimate strengths and the load-slip relationships for composite beams with HSFGB shear connectors. [ABSTRACT FROM AUTHOR]

This study develops four finite elements (FEs) for the analysis of wide-flange steel beams reinforced with a glass fiber-reinforced polymer (GFRP) plate bonded together via an adhesive layer. The formulations treat each of the steel beams and GFRP plates as Vlasov-Gjelsvik thin-walled beams. Two elements are based on shear-deformable kinematics, whereas the other two are based on non-shear-deformable kinematics. The formulations capture the longitudinal-flexural and lateral-torsional responses of the system. Results are then compared with three-dimensional FE analysis solutions based on a current computer program, and the importance of incorporating shear-deformation effects is illustrated, particularly when predicting predominantly torsional responses. The formulation is used to investigate the interaction effect of the shear modulus of the adhesive layer and the length of the GFRP plate. [ABSTRACT FROM AUTHOR]

Three bridges were recently constructed in Missouri using a new type of hybrid composite beam (HCB) incorporated within traditional RC deck systems. These HCBs are comprised of three main subcomponents: a composite shell, compression reinforcement, and tension reinforcement. The compression reinforcement is a self-consolidating concrete (SCC) arch that is tied at the ends by high-strength galvanized steel strands. The compression and tension reinforcements are encapsulated in a glass fiber-reinforced polymer (GFRP) box, and the voids are filled with polyisocyrunate (polyiso) foam. This unique configuration aims to optimize the structural performance of the HCB constituents, hence optimizing the overall performance of the beam. However, because of the novelty of the HCB, its structural behavior is not yet completely understood. Consequently, the finite-element (FE) modeling of this new type of beam is crucial for providing deeper insight into its structural behavior and validating the current design assumptions. It is, therefore, the main goal of this study to examine the accuracy of linear FE analysis (FEA) in predicting the static behavior of the HCB under service loads. This paper explains in detail the FE modeling of the superstructure of one of the recently constructed HCB bridges, using two commercial FEA packages. A field load test that simulates several load cases was applied to the bridge, and the deflections of the HCBs were measured at different locations. A simple analytical procedure that is based on the transformed area method is also used to predict the HCB deflections. The comparison between measured deflections and predicted deflections shows that the FEA can predict the HCB bridge behavior with acceptable accuracy, whereas the theoretical procedure significantly overestimates the beams' deflections. Finally, the two FE models are used to analyze the behavior of the HCBs. [ABSTRACT FROM AUTHOR]

In this two-paper contribution, a general formulation for the nonuniform warping analysis of composite beams of arbitrary simply or multiply connected cross sections, under arbitrary external loading and general boundary conditions, is presented. Part I is devoted to the theoretical development and numerical implementation of the solution method, whereas Part II discusses the examined numerical applications illustrating the efficiency, accuracy, and range of applications of the proposed method as well as the effects arising because of nonuniform warping. The nonuniform warping distributions are taken into account by using four independent warping parameters multiplying a shear warping function in each direction and two torsional warping functions, respectively, which are obtained by solving the corresponding boundary value problems, formulated exploiting the longitudinal local equilibrium equation. A shear stress correction is also performed to improve the stress field arising from the kinematical considerations used. Ten boundary value problems are formulated with respect to the displacement and rotation components as well as to the independent warping parameters and solved using the analog equation method, a boundary element method (BEM)-based technique. The warping functions and the geometric constants including the additional ones due to warping are evaluated with a pure BEM approach. [ABSTRACT FROM AUTHOR]

In this two-paper contribution, a general formulation for the nonuniform warping analysis of composite beams of arbitrary simply or multiply connected cross sections, under arbitrary external loading and general boundary conditions, is presented. In Part I, the governing differential equations have been derived, leading to 10 boundary value problems with respect to the kinematical components and independent warping parameters as well as to seven two-dimensional boundary value problems for the involved shear and torsional warping functions. The aforementioned boundary value problems for the beam are numerically solved using the analog equation method (AEM), a boundary element method (BEM)-based technique. The warping functions and the geometric constants, including the additional ones due to warping, are evaluated with a pure BEM approach. In this Part II, numerical applications of great practical interest are worked out to demonstrate the efficiency and accuracy of the developed method compared with FEM results and results available in the literature. In these examples, the effects arising owing to nonuniform warping in homogeneous and composite beams are illustrated. [ABSTRACT FROM AUTHOR]

Engineered cementitious composite (ECC) is a class of high performance cementitious composites with pseudo strain hardening behavior and excellent crack control. Substitution of concrete with ECC can avoid the cracking and durability problems associated with brittleness of concrete. In this paper, two series, totaling six steel reinforced beams with various transverse reinforcement ratios, ECC thicknesses, and shear span-depth ratios were tested under reversed cyclic loading. According to the test results, steel reinforced ECC beams show better seismic performance in terms of load carrying capacity, shear resistance, energy dissipation capacity, and damage tolerance compared with steel reinforced concrete beams. The extent of load capacity improvement strongly depended on the failure mode. Beams failed in shear showed more significant improvement than those failed in flexure. For the ECC/concrete composite beam, strategic application of ECC can lead to an increase of energy dissipation capacity. For the steel reinforced ECC beam without stirrups, final failure occurs in shear. However, the ultimate load capacity and deformation are comparable to the steel reinforced concrete beam with properly designed stirrups, and the failure process is ductile due to the strain hardening behavior of ECC materials. [ABSTRACT FROM AUTHOR]

For partial-interaction composite beams, two beam theories (i.e., the Euler-Bernoulli and Timoshenko beam theories) are usually used to investigate their deflections, slips, and stress resultants. However, the relationships between the solutions of partial-interaction composite beams based on the two beam theories have not been discussed while the corresponding relationships for homogeneous beams have been investigated in detail for several years. By analyzing the constitutive relationships and equations of equilibrium, the authors derived the relationships of the solutions between single-span Euler-Bernoulli and Timoshenko partial-interaction composite beams. The integral constants are also presented for various boundary conditions. Through the presented relationships, the solutions of the Timoshenko partial-interaction composite beams could be readily obtained from the solutions of the corresponding Euler-Bernoulli counterparts. As a result, the more complicated flexural-slip-shear deformation analysis based on Timoshenko beam theory may be avoided for engineering designers. [ABSTRACT FROM AUTHOR]

The topic of the present paper is a damage detection technique based on the theory of proper orthogonal decomposition (POD). Numerical examples and experimental verification are conducted on an aluminum plate. The numerical examples provide useful information on the effect of several parameters, such as damage severity, type of excitation, noise level, and grid size of the sensors and on the reliability of the technique. The experimental verification using the POD method on the acceleration data show that it is possible to locate some defects in a cantilever plate; however, the analysis of the experimental data highlights the sensitivity of the method to the modification of the boundary conditions. Finally, the application of this technique to the detection of delamination in composite materials is conducted numerically on a cantilever beam. A three-dimensional model was used to investigate how the position of the damage along the length and thickness of the beam is detected and to demonstrate the sensitivity of the method to the location of the sensors with respect to the position of the damage. [ABSTRACT FROM AUTHOR]

The use of fiber-reinforced polymer (FRP) reinforcement in structural engineering has attracted great attention due to high tensile strength, good fatigue performance, and inherent corrosion resistance. Engineered cementitious composite (ECC) is a class of high-performance cementitious composites with pseudo-strain-hardening behavior and excellent crack control. Substitution of concrete with ECC can avoid the cracking and durability problems associated with brittleness of concrete. In this paper, six FRP-reinforced ECC, or ECC/concrete composite beams with various longitudinal and transverse reinforcement ratios and ECC thicknesses, are tested in bending. According to the test results, FRP-reinforced ECC beams show much better flexural properties in terms of load-carrying capacity, shear resistance, ductility, and damage tolerance compared with FRP-reinforced concrete beams. For the FRP-reinforced ECC beam without stirrups, final failure occurs in shear. However, the ultimate load capacity and deformation are comparable to the FRP-reinforced concrete beams with properly designed stirrups, and the failure process is ductile due to the strain hardening behavior of ECC materials. For ECC/concrete composite beams, strategic application of ECC can lead to considerable increase of energy dissipation capacity. When a layer of ECC is placed in the tension zone, the crack width along the beam can be well controlled. High residual strength and stiffness of the composite beam can hence be obtained. In addition to experimental work, a theoretical model is proposed to predict the moment-curvature responses of FRP-reinforced ECC beams. Model results are found to be in good agreement with test data. Theoretical analysis is then conducted to illustrate the effect of reinforcement ratio, compressive strength, and thickness of ECC on the ultimate moment, curvature and ductility of beams. [ABSTRACT FROM AUTHOR]

This paper is devoted to the analytical and numerical modeling of the lateral-torsional stability of horizontally layered composite beams. Composite beams are classified as horizontally layered beams with interlayer slip or sandwich beams with a weak shear core. The governing differential equations of the out-of-plane behavior of horizontally layered composite beams are supported by variational arguments. In the theoretical analysis, a distinction is made between the influence of the shear connection at the interface with respect to the in-plane or transversal deformations and to the out-of-plane or lateral deformations, respectively. Some engineering results are presented for a partially composite beam under pure bending moment. In the case of noncomposite in-plane action (orthotropic connection), a simple closed-form solution is derived for the lateral-torsional buckling moment, and it is shown that the exact dimensionless buckling moment depends only on two structural parameters for beams composed of two identical subelements. The results are analogous to those obtained for the in-plane buckling of partially composite or sandwich-type beams, where the buckling moment increases with the stiffness of the shear connection. Prandtl's valid solution for lateral-torsional buckling of ordinary beams is also found for composite beams in the case of noncomposite action in both the transversal and lateral directions. A generalization of Prandtl's valid solution for composite beams with partial composite action in the lateral direction and noncomposite action in the transversal direction is derived. It is shown that the lateral-torsional buckling formulas are strongly affected by the kinematics of the connected shear layer. Also, the lateral-torsional buckling of partially composite beams with both in-plane and out-of-plane slip behavior is analyzed using the Rayleigh-Ritz method. This mathematical problem leads to a system of differential equations with nonuniform coefficients. An approximated solution is derived for the isotropic connection with isotropic noncomposite actions, whereas an exact solution is presented for the orthotropic connection with noncomposite in-plane action. Finally, the Rayleigh-Ritz approach is compared with some numerical results associated with the exact resolution of the differential equations with nonuniform coefficients. The Rayleigh-Ritz approach appears to be efficient to capture the main phenomena, including the nonmonotonic dependence of the buckling load to the connection parameter. [ABSTRACT FROM AUTHOR]

The analytical solution of a buckling force of a pretwisted delaminated composite column with a proper consideration of the extensional and bending stiffness coupling and transverse shear effect is presented. The system of homogenous linearized differential equations with nonconstant coefficients obtained for this problem is solved with the help of the mathematical theory of analytic differential systems. The parametric studies are presented considering the effect of slenderness, the length of delamination, the asymmetrical position of delamination, and the transverse shear on the critical buckling force. [ABSTRACT FROM AUTHOR]

The objective of the present paper is to analyze the free vibrations of thin-walled beams with arbitrary open cross section, made of cross-ply laminates with midplane symmetry, by means of an exact solution. The theory of thin-walled composite beams is based on assumptions consistent with Vlasov's beam theory and classical lamination theory. The governing differential equations for coupled bending-torsional vibrations were obtained using the principle of virtual displacements. To simplify the coupled system of differential equations, an ideal center of gravity and shear center were introduced. In the case of a simply supported thin-walled beam, the closed-form solution for the natural frequencies of free harmonic vibrations was derived. The frequency equation, given in determinantal form, is expanded in an explicit analytical form. To demonstrate the validity of this method, the natural frequencies of nonsymmetric thin-walled beams having coupled deformation modes are evaluated and compared with results available in the literature as well as with FEM results. [ABSTRACT FROM AUTHOR]

In this study, the cyclic seismic performance of a concrete-filled U-shaped steel beam to H-shaped steel column connections was experimentally evaluated. The concrete-filled U-shaped steel beams were compositely attached to the concrete floor slab. The test was conducted in two stages. The first testing program was carried out on one-sided moment connections to find the most promising connecting scheme. The strengthening scheme, or welding steel plates to the beam bottom flange with minimized stress concentration, was shown to be the most satisfactory, and it was used in the second-stage test on two full-scale cruciform specimens. Considering the unique constructional nature of the proposed composite connections, the critical limit states such as weld fracture, local buckling, concrete crushing, and rebar buckling were carefully addressed in designing specimens. Test results showed that the connection details and design procedures proposed in this study can successfully control the critical limit states mentioned previously. The proposed connection detail successfully pushed the plastic hinging to the tip of the strengthened zone as intended in design, thus effectively protecting the more vulnerable beam-to-column welded joint. The specimens typically exhibited a maximum story drift capacity of more than 5.5% rad, exceeding the minimum limit of 4% rad required of special moment frames. Four of the five specimens tested in this study eventually failed because of a low-cycle fatigue fracture across the beam bottom flange at a high story drift greater than 5.0% rad. [ABSTRACT FROM AUTHOR]

Dynamic response of composite beams with partial interaction is presented using a one-dimensional finite-element model based on a higher-order beam theory. The proposed model takes into account the effect of partial shear interaction between the adjacent layers, as well as the transverse shear deformation of the beam. A third order variation of the axial displacement of the fibers over the beam depth is taken to have a parabolic variation of shear stress, which vanishes at both the top and bottom fibers of the transverse composite surface, as clearly derived on the free and tangentially unloaded surface of the continua. In the proposed finite-element model, there is no need to incorporate any shear correction factor, and the model is free from the shear locking problem. The proposed numerical model is validated by comparing the results with those available in the literature. Many new results are presented, because there are no published results on vibration and buckling of composite beams based on higher-order beam theory. [ABSTRACT FROM AUTHOR]

Timber-concrete composite beams are statically indeterminate structures where a concrete topping is connected via shear connectors to a timber beam. Because effects such as drying shrinkage of concrete, variations of timber moisture content, and environmental temperature cannot freely occur, self-equilibrated stresses (eigenstresses) and additional deflection are induced in the composite beam and may reduce the structural safety at ultimate and serviceability limit states, respectively. The paper presents a simplified design approach suitable for implementation in codes of practice to account for these effects, which are all transformed into uniformly distributed loads to be combined with gravity load. The moisture content variations to consider in design are tabled based on climatic region, size of the timber section, type of exposure, and protective coating. These variations may become significant particularly for the deflection of composite beams with narrow timber sections exposed to outdoor sheltered conditions. Environmental variations and drying shrinkage of concrete are quite influential on the design, particularly when this is governed by deflection control at a serviceability limit state. Composite beams with solid timber slabs and stiff connection, and composite beams with narrow timber section exposed to outdoor conditions were found to be particularly sensitive to these environmental effects. [ABSTRACT FROM AUTHOR]

The fiber-reinforced polymer (FRP) plate or sheet debonding or cover delamination (concrete cover separation) failure mode in externally strengthened reinforced concrete beams has attracted a lot of attention. In this paper, a closed-form analytical solution is developed to determine the nonlinear shear stress distribution along the laminate interface and cover area for any load stage assuming a perfect bond. Trilinear moment-curvature and moment-extreme compression fiber strain is assumed to realize the analytical results. By differentiating the FRP axial tension force with respect to position along the beam, closed-form derivatives in terms of curvature and extreme compressive fiber strain are obtained. The results show three distinct regions of constant or stepwise linear shear distribution in each. These correspond to the uncracked, postcracked, and postyielded zones of the shear span. The results are shown to yield an exact match to those numerically obtained by dividing the shear spans into a large number of small segments and applying nonlinear sectional analysis in the middle of each segment. The analytical solution also compares well with the finite-element results using ABAQUS. The analysis of a number of strengthened beams at experimental debonding or cover delamination failure load show that the interface shear stress distribution varies from cases having no cracking at the plate tip (three regions) to those encountering two regions only (postcracked and postyielded) when the FRP plates or sheets extend close to the supports. It also shows that this distribution, at failure, consists of two regions in most of the cases and may only have a postcracked region in beams with relatively shorter plates or sheets. [ABSTRACT FROM AUTHOR]

An experimental study on the flexural and shear behavior of the full-scale glue-laminated composite sandwich beams in three different layouts was conducted to evaluate the suitability of this construction system for railway turnout sleepers. The building block of this innovative beam is a novel composite sandwich structure made up of glass fiber composite skins and modified phenolic core material that has been specifically developed for civil engineering applications. The sandwich beam is produced by gluing layers of fiber composite sandwich structure together in flatwise (horizontal) and in edgewise (vertical) orientations. The glued sandwich beams with edgewise laminations presented appropriate strength and stiffness for replacement turnout timber sleeper. The mechanical properties of these glue-laminated sandwich beams are comparable with the existing timber turnout sleepers, demonstrating that the innovative composite sandwich beam is a viable alternative sleeper material for railway turnouts. From this study, it is concluded that the glue-laminated composite sandwich structures have the potential to be used for replacement railway turnout sleepers. An enhanced understanding of the behavior of fiber composite sandwich structures for potential civil engineering applications is also an outcome of this investigation. [ABSTRACT FROM AUTHOR]

The shear behavior of reinforced ultrahigh toughness cementitious composite (RUHTCC) beams without transverse reinforcement was investigated in the present paper, in which UHTCC has tensile strain-hardening behavior due to the steady propagation of multiple fine cracks. A total of 15 simply supported beams were subjected to a concentrated load at midspan, of which nine beams were RUHTCC beams and six beams were RC counterpart beams. The varied parameters were shear span-effective depth ratio and longitudinal reinforcement ratio. The experimental results showed that an enhanced ultimate shear strength that was about two times larger than that of an RC beam was obtained for slender beams with use of UHTCC, whereas only a marginal improvement was obtained for short beams. All tested RUHTCC beams presented a diagonal multiple-cracking mode and a stable diagonal crack propagation process. The maximum crack width was controlled within 0.1 mm at the service state and the high postcracking shear reserve strength was obtained, which means that there is no need to limit the minimum web reinforcement ratio in the engineering design for a RUHTCC beam. On the basis of the present test and tests by other investigators, a group of empirical formulae are suggested for predicting the ultimate shear strength of fiber-reinforced beams without stirrups. A good agreement between the predicted strength and tested value was shown, with the mean and coefficient of variation of the ratio between them about 1.02 and 0.10, respectively. [ABSTRACT FROM AUTHOR]

Timber-concrete composite beams are an increasingly common design solution for medium-to-long span floors in new buildings. Thus, there is a significant need for accurate models and analysis tools to predict the response and performance of timber-concrete composite beams. In this paper, a nonlinear finite-element (FE) frame model with deformable shear connection is adopted to estimate the short-term structural response of timber-concrete composite beams for which experimental results are available. The FE model is used in conjunction with a probabilistic analysis methodology, which explicitly accounts for the uncertainties in the parameters that describe the constitutive models for timber, concrete, and shear connectors. The objectives of this study are (1) the evaluation of the variability of global and local structural response quantities owing to the uncertainties in the constitutive parameters of timber, concrete, and shear connectors; and (2) the analysis of the correlation between experimental measurements and numerical results based on FE models in which the values of the constitutive parameters are set equal to their experimentally identified mean values and in which the values of the constitutive parameters are optimized through FE model updating, respectively. The results presented in this study show that uncertainties in the constitutive parameters of timber, concrete, and shear connectors have a significant influence on the correlation between the experimental and numerical results. In addition, the optimal values of material parameters obtained using the FE model updating procedure may show substantial variations with respect to the parameters' mean values as identified in the experimental testing. Prospective developments directed toward design applications and based on the obtained results are also discussed. [ABSTRACT FROM AUTHOR]

This work presents the principle of virtual work and reciprocal theorem of partial-interaction composite beams. The principle of minimum potential energy is also obtained and proved along with the variational formulae for the frequency of free vibration and the critical load of buckling of partial-interaction composite beams. Approximate solutions for bending, vibration, and buckling are finally given to demonstrate their applications. It is shown that the deflections, resonant frequencies, and critical loads of buckling of composite beams under different boundary conditions can be readily obtained with enough accuracy by using these variational principles. [ABSTRACT FROM AUTHOR]

This paper describes the behavior of wood-concrete composite beams in which the wood layer is composed of recycled utility poles. Two full-scale laboratory specimens of 7,500-mm (295-in.) span were constructed, with the concrete slab cast on the timber poles left unshored. The connection was obtained by cutting six notches in the timber poles. A threaded steel dowel is placed in each notch extending through both layers with a nut on the bottom of the beam that can be tightened once the concrete has cured. Since the material in each layer exhibits a time-dependent response, it is necessary to examine the effects of sustained loading. After 28 days of initial curing of the concrete layer during which the midspan deflection was monitored, both beams were subjected to the service load to estimate the composite efficiency. The beams were very stiff and values of 96% and 98% were obtained, respectively, demonstrating the high efficiency of the notched connection system used. A comparison was made with results obtained in the literature for ramp load tests of two similar specimens, which had exhibited composite efficiencies of about 94% and 96%, respectively. A sustained load of approximately 11% of the estimated static ultimate load capacity was then applied to one of the specimens, which was monitored over time. The applied load resulted in a midspan moment of 24 kN·m (212 kip·in.) while the calculated ultimate capacity corresponded to a midspan moment of 226.5 kN·m (2,005 kip·in.). The final deflection was found to increase to 44.4 mm (1.75 in.) after 256 days, which was more than twice the initial elastic deflection owing to the application of the dead and live loads. The deflection attributable to the dead load was 19.1 mm (0.75 in.), and the deflection attributable to the live load was 2.54 mm (0.10 in.). An existing one-dimensional (1D) finite-element program was utilized to predict the time-dependent deflection at the end of a 50-year service life. The comparison with experimental results showed good approximation, particularly for the midspan deflection. The software predicted a 54-mm (2.14-in.) midspan deflection at the end of a 50-year service life, corresponding to 1/139 of the span. This was sufficiently high to suggest that either larger cross-section and/or precambering of the wood layer could be needed when the serviceability limit state of maximum deflection in the long-term is a required performance criterion. [ABSTRACT FROM AUTHOR]

This paper reports the experimental results of symmetrical push-out tests performed on notched and toothed metal plate connectors for laminated veneer lumber (LVL)-concrete composite floor systems. The characteristic shear strength and slip moduli were evaluated for three types of connectors: (1) a 300-mm-long rectangular notch cut in the LVL joist and reinforced with a 16-mm-diameter lag screw; (2) a triangular notch reinforced with the same lag screw; and (3) two 333-mm-long toothed metal plates pressed in the lateral surface of two adjacent LVL joists. The shear force versus relative slip relationships are presented together with analytical prepeak and postpeak approximations which can be used to carry out nonlinear finite-element analyses of LVL-concrete composite beams. The failure mechanisms of the notched connections are also discussed. Analytical design formulas for shear-strength evaluation of notched connections derived in accordance with New Zealand Standards and Eurocodes are proposed based on four possible failure mechanisms. Good approximation was found if a slight modification of the Eurocodes formulas is introduced. [ABSTRACT FROM AUTHOR]

The composite interaction in timber-concrete beams is usually achieved with mechanical devices, such as shear connectors or plates driven into the materials. However, this connecting system shows some inherent inconveniences, such as the need for drillings and the limited mechanical improvement owing to interface slip. Using adhesives instead of mechanical connectors might attenuate these drawbacks. However, engineers are hesitant to apply adhesives for structural purposes, mostly because of the different thermohygrometric behavior of the adhesive and the connected material(s). This is particularly concerning timber because its hysteretic response to moisture may cause interface delamination. Therefore, as a preliminary stage for the test of composite beams, an extensive experimental campaign on small-size specimens was performed. The study focused on the shear strength at the interface and the role of some factors. Several series were considered by changing those parameters, and the results were compared. Both prefabricated and cast-on-site concrete specimens were considered. The results show that this system looks suitable for structural application, at least under steady dry conditions. [ABSTRACT FROM AUTHOR]

This paper reports an experimental program on composite timber-concrete beams with glued interface. The test results are compared to those provided by an analytical model based on the assumption of a fully composite behavior. Both cast-on-site and prefabricated composite timber-concrete beams were produced, aimed at simulating rehabilitation situations or the possibility of a partial or of a full prefabrication of the composite element. Timber-concrete beams with dowel-type shear connectors were also produced and tested for comparison. The results show that the strength is similar, but the glued beams displayed a larger stiffness and, consequently, smaller deflections, which may be of relevance in design. The results also show that, at least under stabilized and dry room conditions, the prevailing mode of failure is tension in timber and, when shear failure occurs, it is mostly conditioned by the shear strength of the concrete or the timber, not by that of the adhesive. As the system depends on the shear strength of the interface, a preceding program consisting in tests on small-size composite specimens was undertaken and is reported in a companion paper. [ABSTRACT FROM AUTHOR]

Flooring systems containing steel-concrete composite beams are common in steel frame structures and it is widely recognized that their behavior under fire loading is profoundly different to that of simply supported composite beams under fire loading. This difference in behavior is due to the presence of restraints provided by cooler members in a compartment fire in a composite frame structure and there is extensive evidence from fire tests that composite beams with unprotected steel components in steel frames perform much better than simply supported composite beams with unprotected steel components. In order to model the structural response of a composite beam restrained in this way at elevated temperature, recourse is needed to a geometric nonlinear formulation, since the transverse beam deflections are large and interact with the substantial axial compressive force in the member at the early stages of the fire. This paper presents such a formulation, which incorporates partial interaction between the concrete slab and steel component, as well as the degradation of the stiffnesses of the components of the composite beam prior to yield at elevated temperature. The generic technique that is developed is shown to agree with solutions reported elsewhere and provides a structural model for the response of a composite beam in fire with the potential for inclusion in prescriptive code rules for rational fire engineering based designs. [ABSTRACT FROM AUTHOR]

This paper presents an experimental program designed to examine the long-term behavior of composite steel-concrete beams under sustained loads. The test program consisted of two simply supported beams under positive bending moments and two cantilever beams under negative bending moments. Long-term deflections, strains, and the cracking behaviors of the specimen beams were monitored over a period of 3 years. The primary observations are: (1) the deflection of the simply supported beam under positive bending moment increased quite significantly over the time due to creep and shrinkage, with the midspan deflections after 3 years of loading reached 2.5 times of the initial deflections, and (2) the cracking of concrete occurred in hogging moment regions for cantilever beams due to the combined effects of concrete shrinkage and sustained negative bending moments. Current design codes were evaluated through a comparison between the calculations and testing results. It was found that the effective modulus method provides a satisfactory prediction on deflections and strains for beams under positive bending moments. But for beams under negative bending moment, the stiffness reduction due to cracking effect should be considered in calculation. [ABSTRACT FROM AUTHOR]

The creep, shrinkage, and cracking of concrete may induce time-dependent changes in the stresses, internal forces, and deflections of steel-concrete composite beams. This paper presents an analytical model to consider these effects in analyzing the long-term behavior of composite beams under service loads using the step-by-step procedure. Under negative moments, the model accounts for the cracking, stress relaxing, tension stiffening, creep, and shrinkage of concrete. Meanwhile, a method is proposed to calculate the maximum crack width of the concrete slab by considering the shrinkage and creep effects. Four composite beams continuously loaded for about 3 years were analyzed using the proposed model. A good agreement is observed between the experimental results and the calculations by the proposed model. A discussion is also made about the aging coefficients in the age-adjusted effective modulus method under different loading conditions. [ABSTRACT FROM AUTHOR]

The long-term behavior in the service stage of continuous composite steel-concrete beams with deformable connectors subjected to uniaxial bending and axial load is presented. The problem is dealt with by recurring to the displacement method, assuming the bending curvature and the longitudinal deformation as unknowns, and obtaining a system of differential and integro-differential equations. The results are compared with literature experimental tests. A case study is then discussed, referring to a continuous beam subjected to permanent and variable loads, to concrete shrinkage, and to a vertical displacement imposed to the central support or to the prestressing of the central part of the beam. [ABSTRACT FROM AUTHOR]

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

The paper investigates the design of continuous steel-concrete composite beams with compact cross section using the elastic analysis with limited redistribution. The permissible moment redistribution which satisfies the requirements of the ultimate limit state (collapse) and serviceability limit state (crack width in the concrete slab) was computed. An advanced finite element program accounting for all mechanical nonlinearities and time-dependent phenomena (creep and shrinkage of concrete) was used. An extensive parametric analysis aimed to determine the influence of several geometrical parameters on the permissible moment redistribution was carried out on propped cantilevers and fixed-end beams. The analyzed parameters include the shape of the steel profile, the ratio between the depths of concrete slab and steel beam, the steel to concrete area ratio, and the reinforcement percentage of the concrete slab. The analysis was limited to compact steel sections (AISC 360-05) or class 1 steel sections (Eurocode 3) and low ductility reinforcing steel (elongation at maximum load [variant_greek_epsilon]ru=2.5%). The moment redistribution domain which satisfies the rotation compatibility in the critical sections, due to the attainment of the rupture of the reinforcement or the local buckling of the steel profile, and the control of cracking (<0.3 mm) in service was evaluated and compared with the limits recommended by current codes of practice. A proposal for the allowable moment redistribution domain according to the limits of the study was given. [ABSTRACT FROM AUTHOR]

Deformation calculation of prestressed continuous steel-concrete composite beams accounting for the slip effect between the steel and concrete interface under service loads is analyzed. A simplified analytical model is presented. Based on this model, formulas for predicting the cracking region of concrete slab near the interior supports and the increase of the prestressing tendon force are derived. A table for calculating the midspan deflection of two-span prestressed continuous composite beams is also proposed. It is found that the internal force of the prestressing tendon under service loads can be accurately calculated using the proposed formulas. By ignoring the increase of the tendon force, the calculated deflection are overestimated, and considering the increase of the tendon force can significantly improve the accuracy of analytical predictions. As the calculated values show good agreement with the test results, the proposed formulas can be reliably applied to the deformation analysis of prestressed continuous composite beams. Finally, based on the formulas for calculating the deformation of two-span prestressed continuous composite beams, a general method for deformation analysis of prestressed continuous composite beams is proposed. [ABSTRACT FROM AUTHOR]

This paper presents a fully developed nonlinear analytical (exact) model for analyzing composite beams under transverse bending load. The model reproduces the elements responsible for the relative slip between the layers (shear connectors and interface) with an elastoplastic strain-softening interlayer. Further than the slip, the model predicts stresses due to a given load and ultimate load for debonding of bilayered composite beams. All the details on the mathematical development are presented. This paper advances the state of the art, since the last development available in literature is an analytical (nonexact) linear model. A number of parametric studies are conducted to evaluate the influence of various geometrical and material parameters, the main results of which are presented together with the interpretation, e.g., the dependence of load-carrying capacity, stresses, and deflection on the local nonlinear load-slip relationship. The research proves as well that the shear connection lower and upper bounds (respectively, totally flexible and infinite rigid shear connectors) do not imply any lower and upper bound for the response. [ABSTRACT FROM AUTHOR]

Eleven steel-concrete composite beams, four under pure torsion, and seven under combined bending and torsion were tested to study their torsional behaviors. Torsion-dominated and bending-dominated failure modes were observed, depending on the ratio between the applied bending and torsional moments. Testing results also showed that the reinforced concrete slab contributes mainly to the torsional resistance of composite beams and the contribution of steel joists to torsion is negligible. However, the steel joist plays a vital role in restraining the concrete slab from deforming longitudinally, which enhances the torsional strength of the concrete slab. Based on the experimental observations, a three-dimensional behavioral truss model capable of analyzing composite beam sections subjected to the combined bending and torsion was presented. In this model, the section is subjected to one- and two-dimensional stresses separately. The former resists the longitudinal stresses due to bending and torsion while the latter resists the shear stresses due to torsion. These two systems are related based on the compatibility of strains and the equilibrium of stresses in the longitudinal direction. The results predicted with this method are in good agreement with those obtained from the tests. Additionally, the interaction between bending and torsional strengths was discussed. [ABSTRACT FROM AUTHOR]

Current American Association of State Highway and Transportation Officials (AASHTO) bridge specifications for compact composite steel girders in positive bending with adjacent compact pier sections limit the allowable maximum strength to a value between the full plastic moment and the hypothetical yield moment of the cross section as a function of the depth of web in compression. The strength prediction equations derived using these methods provide conservative values when compared to the results of the parametric studies used to develop the equations. Recent experimental tests coupled with finite-element analysis and mechanistic evaluations of the cross-section flexural capacity suggest that larger capacities may be achieved than those determined from AASHTO’s prediction equations. This paper presents an assessment of the behavior of composite positive bending specimens. A summary of a comprehensive literature review is provided coupled with results of the analytical and experimental evaluation of the nominal moment capacity of composite girders. Lastly, a less conservative design moment capacity expression developed from this assessment is provided. [ABSTRACT FROM AUTHOR]

There are many situations where strengthening might be required for a nonprismatic reinforced concrete section (i.e., a beam or slab where the depth of the section varies along its length). For example, many bridges in the United Kingdom have inadequate capacity to carry accidental vehicle loads on verges. These shallow depth verges are often cantilevered from the much deeper main bridge deck. The cantilever might be strengthened by applying fiber-reinforced polymer (FRP) composites to the top surface of the cantilever, extending transversely onto the bridge deck. However, a problem may exist with such a situation due to the potential for a dramatic reduction in the degree of strengthening which is achievable. This is due to the effects of cracking, and longitudinal shear stresses. Tests presented in this paper demonstrate that in regions where little or no cracking occurs, local or global debonding of the external FRP may result. Therefore, the strength of some nonprismatic beams, as predicted by current design guidelines, is often shown to be overly conservative and, in one case significantly unconservative. However, more importantly, the predicted failure modes and FRP strains often do not correspond to those observed. Advice on the best approach for analyzing these beams is given. [ABSTRACT FROM AUTHOR]

Composite steel-concrete bridges constitute a major portion of the national bridge inventory. Many of these structures are approaching or have passed their service lives and are in need of repair and rehabilitation. External prestressing by means of high-strength bars or cables attached to the steel beams has been used as an effective technique for upgrading the load carrying capacity of composite steel-concrete girders. While several researchers have investigated the static behavior of prestressed composite beams, few have reported on the fatigue strength of this structural system. The writers present the results of the experimental and analytical study of ten composite girders that were prestressed with seven-wire strands and then fatigue tested to failure. Three methods of extending the fatigue life of cracks were then explored: (1) drilling a hole at the crack tip and installing a high-strength bolt; (2) splicing the web at the cracked section; and (3) increasing the prestressing force of the tendon. The efficacy of the three methods is compared. [ABSTRACT FROM AUTHOR]

The paper investigates the stiffness and strength of composite laminated veneer lumber (LVL) and concrete beams intended for use in long-span flooring systems. Quasi-static bending tests and impact tests were conducted on four, 6 m long specimens to observe the failure mechanisms and to estimate the static and dynamic properties of the systems. One specimen, with a plain LVL member, a strong shear connection, and a concrete slab, was used as a control. The other three specimens investigated the use of (i) a proprietary, lightweight nonstructural concrete panel as a slab; (ii) a straight prestressing tendon and a strong shear connection; and (iii) a draped prestressing tendon and a weaker shear connection. All four specimens had a T-shaped cross section, with the slab supported by either one or two LVL beams. The stiffness of control beam, which is mostly related to the stiffness of the shear connection, is shown to be almost three times that of a bare LVL beam, but the beam is only 74% stronger than the bare beam. The prestressing tendons are shown to have little effect on the stiffness and strength, but reduce the deflection due to permanent load, particularly when they are draped. The proprietary lightweight concrete panels are shown to provide little structural benefit. [ABSTRACT FROM AUTHOR]