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This paper presents experimental and analytical studies on flexural behavior of slab-rib integrated Sandwich composite decks. The influences of layers of glass fiber-reinforced polymer (GFRP) facesheets, foam densities, and the existence of webs and cross beams are discussed herein. The test results showed that the existence of vertical webs remarkably improved the debonding of the facesheets from the foam core, thus increasing the ultimate load by 59% compared with the specimens without webs. However, the existence of horizontal webs has insignificant effect on the failure mode and ultimate load. Increasing the number of layers of GFRP facesheets from 2 to 4 and 6 results in 100% and 214% increments in ultimate loads, respectively, while the specimen with lower density of foam had a higher ultimate load than the specimen with higher density of foam due to deformation compatibility between GFRP skins and foam core with low density. The analysis software Abaqus Explicit was used to simulate the flexural behavior of test specimens, and the numerical results agreed well with the test data. The verified finite element model was extended to analyze the influences of the number of GFRP layers on the top of decks and the height of vertical webs. Based on equivalent method and compatibility of shear deformation, the flexural and shear rigidities were estimated. Then, analytical solution for displacement of the slab-rib integrated Sandwich composite decks subjected to four-point load was derived out. Comparison of analytical and experimental results shows that the displacements can be precisely predicted by the present theoretical model. [ABSTRACT FROM AUTHOR]

In this paper, a new type of connection system was proposed for joints between GFRP-wood composite sandwich beams and columns which were made of glass fiber-reinforced polymer (GFRP) face sheets and southern pine wood cores. The connection system comprised steel angles anchored to the column, and the beam was bolted to the angles. Six different connection system configurations were tested to understand the static behavior of the connection system under different parameters including the length of the beam-closed limb and the presence of ribs. The failure modes of the connection system obtained in tests were of three types: yield failure of the angle steels, local crushing failure of the GFRP-wood composite sandwich beam, and tensile failure of the bolt on the beam-closed limb. The initial rotational stiffness values of the three specimens with ribs were 113.75%, 119.56%, and 227.94% higher than the corresponding three specimens without ribs. And the ductility of connection improved by up to 30.28% due to the presence of stiffener ribs. Based on the tests, the bearing capacity and stiffness of the connection system were predicted. For the specimens without ribs, the method in Eurocode 3 was adopted for bearing capacity and stiffness predictions. For the specimens with ribs, a mechanical model was established for bearing capacity and initial stiffness predictions, which was solved according to the corresponding stress features and failure modes. The analytical results were in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

In this article, the rotational behavior of typical bolted glulam beam-to-column connections with slotted-in steel plate was studied in the numerical method. In order to describe the complicated behavior of wood more closely, an elastic–plastic damage constitutive law combining the Hill yielding criterion and a modified Hashin failure criterion was embedded in the commercial ABAQUS software in the form of a VUMAT subroutine. Subsequently, a three-dimensional finite element model based on the constitutive law proposed was established, with the failure mode and moment–rotation curve compared to some similar experiments. Based on this finite element model, a parametric study concentrating on the influence of the width of the beam, bolt diameter, and assembly clearance was carried out. It was found that the numerical method using the proposed constitutive law showed a good capacity to study the rotational behavior of the connections. Besides, the initial rotational stiffness increased with the increase in beam width and bolt diameter, and the assembly clearances between bolts and bolt holes would affect the initial rotational stiffness while the assembly clearance between beam and column affected little. [ABSTRACT FROM AUTHOR]

This paper reports on the flexural performance of an innovative composite grid panel composed of glass fiber-reinforced polymer face skins and deep glass fiber-reinforced polymer ribs with a trapezoidal cross-section. Three-point and four-point bending experiments were performed to demonstrate the feasibility of the composite grid panels under concentrated loads. Compared with the composite grid panels without skins, maximum increases in the ultimate load, and initial bending stiffness of the composite grid panels of approximately 68.2% and 306.7%, respectively, were achieved with the existence of both upper and lower skins. Furthermore, an analytical analysis was carried out to predict the initial bending stiffness and mid-span deflection of the composite grid panels. A comparison of the analytical and experimental results showed that the analytical model accurately predicted the flexural performance of the composite grid panels subjected to three-point and four-point bending. Failure mechanism maps were constructed to predict the mechanical response and failure modes of the composite grid panels. Moreover, the validated model was used in a parametric analytical study to further estimate the effects of various parameters on the flexural performance of the composite grid panels. The results demonstrated that the initial bending stiffness can be significantly improved by increasing the trapezoidal section ratio, face skin thickness, and grid height. [ABSTRACT FROM AUTHOR]

A composite wrapping system for main cable protection of suspension bridges was designed by using prepreg fiber-reinforced composites and nitrile rubber. The circumferential expansion performance of the system was tested, and the curves of circumferential bearing capacity and radial displacement of the components were obtained. Failure modes of each group of components were compared and analyzed. The results show that most of the components are vertically fractured at the lap transition. The increase of the number of prepreg layers contributed the most to the circumferential bearing capacity of components, with a growth rate of 65.31%~109.01%. The increase of rubber belt layers had the most significant effect on the radial displacement of the components, with a growth rate of 7.06%~23.5%. In the initial stage of the test, the strain of each part of the component was smaller due to the compaction by the loading device, and the strain value of the component was generally linearly increased during the loading process, during which the strain of the overlap was the smallest. The calculated cross-sectional temperature deformation of the main cable is in good agreement with the experimental data. The application of the rubber belt increases the deformation of the main cable; therefore, the protection system for the main cable could have more deformation redundancy and delay the arrival of the ultimate strain of the outer prepreg wrap. [ABSTRACT FROM AUTHOR]

Tooth-plate-glass-fiber hybrid sandwich (TFS) is a type of sandwich composites fabricated by vacuum-assisted resin infusion process, in which glass fiber facesheets reinforced by metal plate are connected to foam core through tooth nails. Bending properties and interlaminar properties of TFS beams with various foam densities were investigated by flexural tests and DCB (double cantilever beam) tests. The test results showed that by increasing the foam core density from 35 kg/m3 to 150 kg/m3, the peak strength of TFS beams significantly increased by 168% to 258% compared with similar sandwich beams with fibrous composite facesheets. With the change of foam density and span length, the main failure modes are core shear and facesheet indentation beneath the loading roller. The interlaminar strain energy release rates of TFS specimens also increased by increasing the density of the foam. In addition, an analytical model was used to predict the ultimate bending strength of TFS beams, which were in good accordance with the experimental results. [ABSTRACT FROM AUTHOR]

• Post-fire failure mode mainly depended on the number of exposed sides and fire damage degree. • Both GFRP and wood exhibited significant recovery in elastic modulus after cooling. • New charring criterion for sandwich based on the critical decomposition degree. • Development and implementation of integrated thermal and thermomechanical models for sandwich in Abaqus. Wood-cored sandwich components have been extensively used in constructions of buildings and bridges. However, the existing studies on the postfire behavior of these components are very limited. This study aims to quantitatively evaluate the postfire residual properties of the pultruded wood-cored GFRP sandwich (PWGS) beams. This paper mainly comprises three parts: (i) review of fire experiment of the PWGS beams; (ii) postfire bending experiments conducted on the PWGS beams with different fire scenarios and (iii) numerical study on thermal and postfire thermomechanical responses. It was found the failure modes mainly depended on the number of exposed sides and the fire damage degree. For the three-sided fire-exposed specimens (except for the one with a 25 mm-thick calcium silica board), the progressive tension rapture of the charred fibers was the dominant failure mode. The other specimens, however, exhibited the brittle in-plane shear failure of the web. Moreover, after cooling down from 250 °C to 20 °C, the GFRP and wood exhibited 68 % and 35 % of recoveries of elastic modulus respectively. A three-dimensional thermal model with kinetic thermophysical sub-models considering heat transfer, water evaporation and decomposition was developed. The developed thermal model accurately predicted the temperature responses and charring profiles. Furthermore, a thermomechanical model considering the material damage was developed to accurately predict the elastic modulus distribution, postfire residual bending capacity and failure modes. This study provides the basis for the retrofit and the reinforcement of the fire-damaged PWGS beams. In the future, study on the fire resistance of the PWGS components in fire will be required. [ABSTRACT FROM AUTHOR]

In this study, the on-axis and off-axis compressive behavior of pultruded unidirectional glass fiber reinforced polymer (GFRP) coupons at elevated temperatures were investigated. The coupons with fiber orientations of 0°, 30°, 60° and 90° to the compressive loading axis were tested from 20 °C to 180 °C. The specimens under on-axis compression clearly exhibited a kinking failure mode at elevated temperatures, while the in-plain shear failure occurred in the specimens of 30° and 60° off-axis compression, and the out-of-plain shear failure occurred in 90° off-axis specimens. The failure modes were hardly affected by the temperatures except that the GFRP skin wrinkling captured in off-axis compression specimens above 60 °C. As expected, the compressive strength and elastic modulus were significantly reduced with the increase in temperature. Moreover, the compressive strength of on-axis and off-axis specimens exhibited similar retention rate at each targeted temperature, while the elastic modulus of on-axis specimens showed a higher retention rate than those of off-axis specimens. The analytical studies showed that the degradation of modulus and strength of all specimens generally followed the inverse rule of mixture. In addition, the off-axis strength and elastic modulus were estimated by the Hankinson's formula. [ABSTRACT FROM AUTHOR]

In this paper, the flexural creep behavior of composite sandwich beams with glass fiber- reinforced polymer (GFRP) face sheets and a balsa wood core was investigated. First, static three-point bending tests for the beams were conducted, and an average ultimate bearing capacity of 6.08 kN was obtained. Then, ten bending creep test devices were designed and manufactured based on the principle of leverage. Creep experiments were carried out for a period of 3000 h at four different load levels corresponding to 20%, 40%, 60% and 80% of the ultimate bearing capacity. The results show that the creep behavior exhibits linear viscoelastic properties when the load level is less than 40%, while creep failure occurs in all specimens at load levels of 60% and 80%. Specimens subjected to the 60% load level exhibit two failure modes, i.e., core shear failure and overall bending failure, while specimens subjected to the 80% load level exhibit only bending failure. Furthermore, the experimental creep curves at the 20% and 40% load levels are successfully fitted by the Bailey-Norton and Findley models, and a life prediction method is proposed to predict the creep life of the beams at any load level. [ABSTRACT FROM AUTHOR]

• The fatigue failure modes of web reinforced GFRP-balsa sandwich beams varied with the web number and load level. • The web reinforced beams still have load-bearing capacities after cracks appeared. • The span-to-depth ratio and web number have significant effects to the S-N curves. • Deflection evolutions can be divided into three stages: transient fall, stable evolution, and rapid failure. • The fatigue damage model followed an exponential-type function was shown to be successful in predicting the fatigue life. This paper investigated static and fatigue bending behavior of sandwich beams using glass fiber reinforced polymer (GFRP) as skins and webs while balsa wood as core The failure modes, S-N curves, load-deflection behavior and stiffness degradation were obtained and compared The results showed that the fatigue failure modes of web reinforced sandwich beams varied with the web setting and load grade The web setting changed the failure mechanism and the materials were utilized in varying degrees in different specimens Fatigue life model based on damage modulus was proposed and proved appropriate to predict the fatigue damage and ultimate life. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel wood-filled glass fibre-reinforced polymer square columns with lattice- web reinforcements are proposed. • The axial compressive behaviour, including the interface bonding properties and compressive damage, is studied. • The lattice-webs greatly improves the stiffness and the collaborative working ability of composite columns. • An analytical model is proposed for evaluating the ultimate load of the specimens. A novel wood-filled glass fibre-reinforced polymer (GFRP) square column (WGSC) with lattice-web reinforcements was proposed. Eight column specimens with varying numbers of face sheets and lattice webs and one control specimen were tested to investigate the compressive behaviour and failure mode of WGSCs. The experimental results reveal that all the specimens with lattice-web reinforcements failed due to crumpling of the face sheets and compressive damage in the core material. With increased number of lattice webs, the ultimate loads of the specimens increased, and pseudo-ductile behaviour was observed. Improvements were also found in the effective constraint and interfacial bonding performance of specimens with lattice-web reinforcements and affected by the number of face sheets. By introducing the concept of the constrained stiffness ratio, an analytical model was proposed for evaluating the ultimate load of the specimens based on Tsai-Wu strength criterion, and the results were consistent with the test data. [ABSTRACT FROM AUTHOR]

• Study on the behavior of plybamboo sheathing-to-framing screwed (PSFS) connections. • Comparison between the behavior of PSFS connections and conventional nail connections. • The influence of representative variables on PSFS connection behavior was evaluated. • The Failure mode and ultimate strength were predicted by the European Yield Model. To encourage more sustainable materials in construction, this study investigates self-tapping screws as a way to optimize the utilization of plybamboo panels in wood-frame shear walls. Twelve groups of plybamboo sheathing-to-framing screwed (PSFS) connections and two comparable groups with OSB sheathings were tested under monotonic loads. Representative variables including sheathing thickness, screw edge-distance and loading direction to framing member were taken into account. The European Yield Model was then adopted to predict the ultimate strength and failure mode of the PSFS connections. Test results indicate that the PSFS connections have much higher elastic stiffness, ultimate strength and deformability than those fastened with common nails. Screw edge-distance and plybamboo sheathing thickness have little effect on the mechanical properties of the PSFS connections, whereas loading direction to framing member is clearly an influencing variable, since the connections under parallel loading show higher elastic stiffness, ultimate strength and ductility than those under perpendicular loading. The European Yield Model can reasonably predict the failure mode of PSFS connections when the plybamboo sheathing has a thickness no less than 12.5 mm, but will underestimate the ultimate strength by 34.2% to 49.9%. [ABSTRACT FROM AUTHOR]

This study investigated the effect of shear span-to-depth (a / d) ratio on the mechanical behavior of composite sandwich beams, composed of glass fiber reinforced polymer (GFRP) skins, balsa wood core, and GFRP ribs. Three-point bending tests were carried out on fifteen specimens to verify the effects of the a / d ratio, varying from 1 to 6, and GFRP ribs on the deflections, failure load, and failure modes of sandwich beams. Test results indicated that the a / d ratio plays a major role in beam deflections, which decreased 74–1418% as the a / d ratio varying from 1 to 6. All beams exhibited deflections at failure of span/124 to span/35. Specimens failed in balsa wood core shear failure while a / d ≤ 4, whereas it failed in top skin compression failure when a / d ratio equal to 6. Increasing the GFRP ribs thickness from zero to 2.4 mm, the failure load of sandwich beams increased by 23–75%. Moreover, the ultimate moment increased by 70–323% as the a / d ratio increases from 1 to 6. In addition, for specimens with a / d equal to 4, the failure load and stiffness of sandwich structures with balsa wood core was 79–209% and 90–246% higher than those of specimens with different densities of light-weight foam core. A simplified analytical model accounting for the influence of GFRP ribs on stiffness and strength of the sandwich beam was developed and validated against experimental results. Analysis shows that flexure became more dominant as the a / d ratio increases. The shear deformation contribution of the balsa wood core is over 50% in beams with a / d ≤ 3, while the value is only 20% for beams with a / d equal to 6. The proposed analytical model which accounts for the combined effect of the GFRP ribs agrees well with the experimental results. • Investigated the effect of shear span-to-depth (a / d) ratio on the mechanical behavior of composite sandwich beams. The a / d ratio plays a major role in beam deflections, which decreased 74–1418% as the a / d ratio varying from 1 to 6. All beams exhibited deflections at failure of span/124 to span/35. The failure load and stiffness of sandwich structures with balsa wood core was increased by 79–209% and 90–246% respectively.. [ABSTRACT FROM AUTHOR]

• The fatigue bending behaviour of GFRP-wood sandwich beams were studied experimentally. • The lattice web greatly improved the ductility performance and the collaborative working ability of sandwich beams. • Weibull distribution equations and the secant stiffness curves were established to predict fatigue lives. Three-point static and fatigue bending experiments were performed on 51 composite sandwich beams with glass fibre reinforced polymer (GFRP) face sheets and paulownia wood cores. Specimens with no lattice, one lattice and two lattices were prepared, and the fatigue bending failure mode, fatigue life distribution and stiffness degradation model of the sandwich beams were obtained. The results show that the specimens with no lattice exhibit two brittle failure modes, i.e., interface debonding and core shearing. The failure modes of the specimens with one lattice are local buckling and crushing, while the specimens with two lattice webs only exhibit tensile failure of the bottom face sheet. Moreover, the specimens with webs exhibit ductile failure characteristics. Based on the Weibull model, the Weibull distribution equations of each specimen under different survival rates were established, and the engineering fatigue curve was drawn. Furthermore, the secant stiffness curve of the specimens with webs was established based on the fatigue cumulative damage theory, and the fatigue lives of three specimens were predicted. [ABSTRACT FROM AUTHOR]

To better understand the bonding performance of glued laminated timbers (i.e., glulams) during fires, phenol–resorcinol–formaldehyde (PRF) and melamine–urea–formaldehyde (MUF) adhesives were used to investigate the effects of elevated temperatures on the glueline shear strength. The wood failure mode was observed to study the heat resistance of the two adhesives. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) were used to analyze chemical and microscopic changes at various temperatures. The parallel-to-grain shear strength of solid larch wood decreased linearly with increasing temperature. Bonding strength of the wood–PRF glueline exposed to elevated temperatures was similar to that of the solid wood. The wood–MUF glueline exhibited good bonding performance at room temperature but showed poor thermal resistance. Shear strength of wood–MUF glueline was 0 MPa at 280 °C. Bonding performances of PRF and MUF deteriorated linearly with increasing temperature. FTIR analysis showed that PRF could maintain a relatively intact chemical structure when the temperature was higher than 150 °C, and the structure of the MUF degraded significantly when the temperature was higher than 200 °C. [ABSTRACT FROM AUTHOR]