Optimum design of cross-sectional profiles of pultruded box beams with high ultimate strength

Pultruded box beams under bending may be subjected to local buckling which causes premature failure of the beams. As such it is important to design pultruded box beams with high local buckling resistance to increase their ultimate strength. This paper presents an optimum design approach for cross-sectional profiles of pultruded box beams of (approximately) the same mass with emphasis on accomplishment of high local buckling resistance through finite element analysis. Five different sectional profiles have been designed by stiffening a simple box, and finite element analysis is used to study linear buckling and postbuckling of the beams. Results for the critical loads of linear buckling and local buckling judged by stress variation, stresses and deformations in postbuckling are presented. The computational results show one of the proposed sectional profiles does not develop local buckling and produces much smaller stresses and deformations within the load range of interest.     

Test on pultruded GFRP I-section under web crippling

This paper presents the details of experimental and numerical research study on web crippling property of pultruded GFRP I-section under concentrated web crippling loadings. A total of 12 pultruded GFRP I-section with different loading conditions and bearing lengths was tested. The experimental scheme, failure modes and load–displacement curves were also presented. The investigation was focused on the effects of different loading condition and bearing length on web crippling ultimate capacity and ductility of pultruded GFRP I-section. The failure mode comprised longitudinal bending main crack, bending wrinkling cracks and shear cracks. Specimens with interior bearing load had slightly higher ultimate strength and greater deformation capacity than those of specimens with end bearing load. The ultimate strengths usually decreased with the increase of the bearing length except IG condition. Finite element models were developed to numerically simulate the tests performed in the experimental investigations by using commercial ABAQUS software. Based on the results of the parametric study, a number of design formulas proposed in this paper can be successfully employed as a design rule for predicting web crippling ultimate capacity of pultruded GFRP I-section under four loading and boundary conditions by using single parameter analysis.     

Post-cracking strength and ductility of glass–GFRP composite beams

This paper presents results of experimental and numerical investigations on the structural behaviour of composite beams made of annealed glass panes and glass fibre reinforced polymer (GFRP) pultruded profiles. The main goal of the transparent structural solutions presented here is to increase the post-cracking residual strength and ductility of glass by using GFRP strengthening laminates. The experimental programme included (i) tensile tests on double lap joints between glass and GFRP pultruded laminates, bonded with different types of structural adhesives, and (ii) full-scale flexural tests on glass beams and glass–GFRP composite beams, with different strengthening geometries and structural adhesives. Results obtained in this study show that, unlike glass beams, in glass–GFRP composite beams it is possible to obtain relatively ductile failure modes, with a significant increase of both strength and deformation capacity after the initial cracking of glass. The stiffness of the structural adhesive used, together with the geometry of the GFRP strengthening element, have a major influence on the structural response of the composite beams. Finite element models were developed for all tested beams, allowing to simulate their serviceability behaviour (prior to glass cracking) with fairly good accuracy, namely in what concerns the degree of shear interaction at the bonded interfaces.     

Tests on GFRP Pultruded Profiles with Channel Section Subjected to Web Crippling

This paper presents an experimental investigation on the web-crippling behavior in glass fibre reinforced polymer (GFRP) pultruded profiles with channel section. A main bending main crack on the web is the main failure mode in the test. The effects of the loading positions, the supporting conditions and bearing lengths on the web crippling behavior of GFRP pultruded profiles with channel section are discussed. Specimens with interior bearing load have higher ultimate strength and all the specimens with loading conditions IG reached the highest ultimate strength but all ruptured. Ultimate strengths of GFRP pultruded profiles with channel section can not be enhanced by increasing the length of the bearing plate. Finite element models were developed to numerically simulate the test results in the terms of ultimate loads, failure modes and load-displacement curves. Based on the results of the parametric study, a number of design formulas are proposed in this paper to accurately predict web crippling ultimate capacity of pultruded GFRP channel sections under four loading and boundary conditions.     

基于套管屈曲约束的拉挤型GFRP管轴压性能

为解决复合材料空间桁架结构部分关键压杆失稳引发的连续性倒塌问题,提出了一种由不锈钢套管及螺栓连接系组成的玻璃纤维增强树脂复合材料(GFRP)管整体失稳套管屈曲约束装置。为分析该套管屈曲约束装置对拉挤型GFRP管轴压性能的影响,对3个GFRP管试件和4个套管屈曲约束GFRP管试件进行了轴压试验,观察了试件的受力过程和破坏形态,获得了荷载-位移曲线和荷载-应变曲线,对比研究了两者的极限承载力和破坏模式,同时利用有限元模型分析了不同内核长细比、内核与套管间隙及套管壁厚对GFRP管轴压性能的影响。结果表明:该套管屈曲约束装置能有效约束GFRP管整体失稳变形,其极限承载力和延性均得到提升,并使GFRP管从失稳破坏向材料强度破坏发展;内核长细比越大,套管屈曲约束GFRP管极限承载力相比于内核失稳临界荷载的相对提升幅值越高,约束效果越好;内核与套管间隙越大,GFRP管延性越好,但其极限承载力会降低;套管壁厚过薄会降低GFRP管极限承载力,过厚则约束效果不明显。      

Lateral buckling of pultruded GRP I-section cantilevers

A series of lateral buckling tests on pultruded GRP I-section cantilever beams is described. Comparisons of the theoretical critical loads, determined from approximate formulae and numerical finite element eigenvalue analysis, with the test results are presented. They reveal that linear buckling analysis does not provide an accurate estimate, for use in design, of the maximum tip load that a GRP cantilever may support. It is concluded that both initial deflections and pre-buckling deformations may need to be accounted for in order to model accurately the response of tip loaded pultruded GRP cantilevers.     

GFRP复合材料-轻木夹芯梁弯曲疲劳性能试验

为研究真空导入成型的玻璃纤维增强树脂基复合材料-Balsa轻木（GFRP-Balsa）夹芯梁弯曲疲劳性能,进行了普通无格构、单格构增强、双格构增强三种类型共42根试件在不同荷载等级下的四点弯曲疲劳试验,得到夹芯梁的弯曲疲劳破坏模式、疲劳寿命和损伤演化规律,分析了三种类型夹芯梁在弯曲疲劳载荷下不同的损伤机制。研究结果发现,无格构夹芯梁的失效模式统一为芯材剪切和面板脱粘,格构增强夹芯梁的失效模式随格构设置及载荷等级变化,主要有上面板屈曲或压坏、下面板拉断等;采用指数经验模型拟合夹芯梁的疲劳荷载-寿命（S-N）曲线,得到三种类型夹芯梁的寿命预测公式;夹芯梁的位移演化历经"位移瞬降-平稳演化-损伤萌生至破坏"三个阶段,相对于无格构试件,格构增强试件在疲劳失效前有较明显预兆。     

Behaviour of hybrid FRP–UHPC beams subjected to static flexural loading

This paper provides the experimental results of a new hybrid beam intended for use in bridge applications. The hybrid beams were made up of pultruded Glass Fibre Reinforced Polymer (GFRP) hollow box section beams strengthened with a layer of Ultra-High-Performance-Concrete (UHPC) on top and either a sheet of Carbon FRP (CFRP) or Steel FRP (SFRP) on the bottom of the beam. Four hybrid FRP–UHPC beams were tested along with one control GFRP hollow box beam under four-point static flexural loading. Two types of beams were tested (Phase I and Phase II), which incorporated different connection mechanisms at the GFRP–UHPC interface. It was concluded that the hybrid beams had higher flexural strength and stiffness than the control beam, where the beams reinforced with SFRP showed greater percent cost effectiveness than beams reinforced with CFRP. In addition, the improved connection mechanism used in Phase II beams was found to provide adequate interface bond strength to maintain full composite action until ultimate failure.     

Time-dependent and residual behavior of pultruded GFRP beams subjected to sustained intensities and cold temperature

This paper presents the time-dependent response and residual behavior of pultruded glass fiber reinforced polymer (GFRP) beams. A total of nine beams are tested in four-point bending. One beam is served as control and eight beams are loaded to failure after exposing to three levels of sustained intensities (20%, 40%, and 60% of the static capacity) at room (25 °C) and cold (− 30 °C) temperatures for 2000 h. Time-dependent material parameters are obtained from the test. Analytical approaches are used to predict the behavior of test beams, based on mechanics-based failure criteria and Findley's creep theory. Three-dimensional finite element models are also developed, based on the experimentally obtained material parameters. The GFRP beams demonstrate time-dependent material degradation due to the sustained load. Cold temperature alters the load-carrying capacity and creep response of the beams. Brittleness of the GFRP is accelerated when the beams are exposed to sustained intensities and cold temperature. The contribution of shear deformation to the deflection of the beams increases with sustained load. Although the proposed modeling approaches agree with the experiment, further development is recommended to account for micro-level material deterioration characteristics.     

外包GFRP板钢筋混凝土梁的抗剪性能研究

该文提出了一种新型的GFRP-钢筋混凝土高耐久性梁,即普通钢筋混凝土梁外包GFRP 板,其中的GFRP板既为防腐保护,又可兼作模板和受力筋。通过对外包GFRP 板钢筋混凝土梁及其普通钢筋混凝土对比梁进行加载试验,研究其受力特点和破坏模式。试验结果表明:和普通钢筋混凝土梁相比,外包GFRP 板钢筋混凝土梁的抗剪承载力有较大幅度提高。对外包GFRP 板钢筋混凝土试验梁的抗剪承载力进行了分析,计算值与试验值吻合较好。     

Delamination and kink-band failure of pultruded GFRP laminates under elevated temperatures and compression

Compression experiments were conducted on slender glass fiber-reinforced polymer (GFRP) laminates at different temperatures in the elevated range. Experimental buckling loads, lateral second-order deformations, and shear strength decreased with increasing temperature until stable values were reached at a much lower level in the leathery material state. The resin-dominated bending stiffness decreased at a higher rate than the fiber-dominated compressive stiffness. Global buckling followed by a delamination failure during the post-buckling process was observed for temperatures below 180 °C, while pre-buckling kink-band failure occurred when the temperature increased to 220 °C. Recently proposed thermomechanical models were further validated and enabled the changing failure mode and associated Tresca and kink-band shear stress and strength conditions to be modeled.     

Fir and chestnut timber beams reinforced with GFRP pultruded elements

High-performance fibers are being widely researched for repair and rehabilitation in civil engineering structures. The potential benefits, liabilities, and architectural considerations regarding the use of high-performance fibers for reinforcing wood beams are discussed. An experimental program based on a four- and three-point bending test configuration is proposed to characterize the stiffness and strength response of wood beams reinforced with pultruded GFRP (glass fibers reinforced polymers) elements. Improving wood mechanical characteristics through the use of fiber reinforced polymers often involves the use of adhesives, generally epoxy resins. For this reason mechanical, calorimetric and thermo-gravimetric analyses were performed on the resin utilized and bonding effectiveness was studied. Mechanical tests carried out on full-scale wood beams showed that the reinforcement with GFRP beams may produce strong increases in flexural stiffness and capacity. In addition, an analytical investigation based on a simple linear analysis was conducted to predict ultimate load. At the end of this paper results of the experimental program are presented and used for comparison with the analytical procedure.     

Seismic retrofit of circular RC columns through using tensioned GFRP wires winding

The aim of this paper is to suggest a jacketing method using glass fiber reinforced polymer (GFRP) wires for reinforced concrete (RC) columns with lap splice of longitudinal reinforcement. For this study, four RC columns were prepared of 400 mm in diameter and 1400 mm in height with an aspect ratio of 3.5; two were lap spliced and the other two had continuous longitudinal reinforcement. One specimen of each of the two types was jacketed by GFRP wires that had a diameter of 1.0 mm. The GFRP wires were tensioned with small force during winding each column. The jacket comprised stepped layers along the variation of bending moment of the column. Cyclic lateral force was applied at the top of the columns, and the top displacement of the columns as well as corresponding force was measured during the bending tests.This study considered the failure of the four tested columns and analyzed their later force–displacement behavior. Additionally, the effective stiffnesses of the force–displacement curves were evaluated. The GFRP wire winding jacket prevented splitting of the lap-spliced reinforcement in the lap-spliced column and delayed buckling of the longitudinal reinforcement. The jacket protected the continuous reinforcement column against steel buckling and concrete spalling off and, thus, induced shear failure in the column. The GFRP wire winding jacket increased the failure drifts of both jacketed columns compared with those of the references.     

Examination of the failure of sandwich beams with core junctions subjected to in-plane tensile loading

The paper concerns local effects occurring in the vicinity of junctions between different cores in sandwich beams subjected to tensile in-plane loading. It is known from analytical and numerical modelling that these effects display themselves by an increase of the bending stresses in the faces as well as the core shear and transverse normal stresses at the junction. The local effects have been studied experimentally to assess the influence on the failure behaviour both under quasi-static and fatigue loading conditions. Typical sandwich beam configurations with aluminium and glass-fibre reinforced plastic (GFRP) face sheets and core junctions between polymer foams of different densities and rigid plywood or aluminium were investigated. Depending on the material configuration of the sandwich beam, premature failure accumulating at the core junction was observed for quasi-static and/or fatigue loading conditions. Using Aluminium face sheets, quasi-static loading caused failure at the core junction, whereas no significance of the junction was observed for fatigue loading. Using GFRP faces, a shift of the failure mode from premature core failure in quasi-static tests to face failure at the core junction in fatigue tests was observed. In addition to the failure tests, the sandwich configurations have been analysed using finite element modelling (FEM) to elaborate on the experimental results with respect to failure prediction. Both linear modelling and nonlinear modelling including nonlinear material behaviour (plasticity) was used. Comparing the results from finite element modelling with the failure behaviour observed in the quasi-static tests, it was found that a combination of linear finite element modelling and a point stress criterion to evaluate the stresses at the core junction can be used for brittle core material constituents. However, this is generally not sufficient to predict the failure modes and failure loads properly. Using nonlinear material properties in the modelling and a point strain criterion improves the failure prediction especially for ductile materials, but this has to be examined further along with other failure criteria.     

Fatigue behaviour of asphalt concrete beams reinforced by glass fibre-reinforced plastics

The aim of this study was to evaluate the enhancement effect of asphalt concrete beams reinforced by glass fibre-reinforced plastics (GFRP). First, the Cooper fatigue test machine was used to conduct the four-point bending fatigue tests. The test results showed that the mean fatigue life of hot mixture asphalt (HMA) beams had been extended to more than 8.81 times with 3-mm thick GFRP sheets pasted on the top. Second, the stress and strian behaviour of the four-point bending fatigue test specimen was simulated by the finite element method. The results showed that flexural stiffness of HMA beams had increased significantly with GFRP sheets pasted on the top. Finally, the fatigue failure process of the HMA beam with GFRP sheet pasted on the top was predicted by the theory of damage mechanics. The predicted results matched well with those obtained in the fatigue tests.Therefore, pasting a GFRP sheet of a certain thickness on a steel bridge deck could greatly improve the overall stiffness of the pavement layer and form a kind of durable steel bridge deck surfacing structure. The research results had important theoretical significance and value in engineering applications.     

Failure investigation of GFRP communication towers

The rapid growth in telecommunication system requires a large number of free-standing and guyed towers. Glass Fiber Reinforced Polymer (GFRP) material is corrosion resistant and light weight with specific gravity one-fourth of steel. In triangular based communication towers gusset plates can be avoided by using GFRP 60° angles for leg members. The failures encountered in the full-scale testing of a 24 m high triangular GFRP communication tower designed by the pultruded profile manufacturer purely based on the properties derived from tensile coupon test results is presented in this paper. The GFRP 60° angles as struts exhibited torsional-flexural buckling mode and the 90° angles failed by flexural buckling. ANSYS Shell 281 layered element used to model the GFRP struts predicted the failure loads closer to the experiments. The GFRP 60° angles as leg members have shown torsional-flexural buckling mode till failure but finally failed by de-bonding of layers in the case of angle sections made of stitched mat and by shearing of the cross section in angles with multi-axial technical fabrics. The 60° angles subjected to compression, exhibited higher strength at a component level compared to the leg member in tower restrained by secondary bracings. The strength and behaviour of GFRP angles with multi-axial technical fabrics (± 45°/90°) are superior compared to the angles with stitched mat.     

System ductility and redundancy of FRP beam structures with ductile adhesive joints

This paper reports on a structural concept for engineering structures composed of FRP components to provide system ductility that compensates for the lack of material ductility inherent to FRP materials. The concept includes the use of redundant structural systems and ductile or flexible adhesive joints. To demonstrate the feasibility of the proposed concept, quasi-static experiments on pultruded GFRP beams were performed. The two-span beams were connected with flexible adhesive joints at the middle support. The flexible joints from highly non-linear adhesives provided a favorable redistribution of the internal and external forces in the statically indeterminate system compared to single-span and continuous beams, which were also examined. In the case of adhesive joint failure, structural collapse was prevented because of system redundancy. Due to the stiffness-governed design of the GFRP beams, the stresses in the flexible adhesive joints were small and creep deformations in the joints could be controlled.     

The static behavior of a modular foam-filled GFRP bridge deck with a strong web-flange joint

The static behavior of a modular bridge deck filled with a low-density polyurethane foam was experimentally investigated. The web-flange joint of the deck was strong enough so that a failure of the deck in the transverse direction was governed by the delamination of the bond between two adjacent modules whether the deck was filled or not. Although the elastic modulus of the foam was only a thousandth of the homogenized modulus of the GFRP deck, the structural performance of the deck in the transverse direction was significantly improved by the foam filled inside the deck. It was shown experimentally that tensile stress could develop in the top flange of the deck subjected to three point bending because of shear deformation. Such a development of tensile stress was significantly mitigated by the foam filled inside the deck.     

Structural response of hyperstatic concrete beams reinforced with GFRP bars: Effect of increasing concrete confinement

The design of concrete structures reinforced with glass fibre reinforced polymer (GFRP) bars is influenced by their reduced stiffness and brittleness. In hyperstatic structures, the methodology used in force analysis depends on the ductility of the structural systems, which in this case, being essentially provided by the concrete, can be potentially increased by confining concrete in critical zones. This paper presents experimental and numerical investigations about the flexural behaviour of continuous beams reinforced with GFRP bars, namely of their service and failure responses, and the effect of increasing concrete confinement in critical cross-sections. A calculation procedure to quantify the confinement effect in beams due to the reduction of the spacing between shear stirrups is first presented. The experimental investigations comprised a comparative study in which two-span concrete beams reinforced with either GFRP or steel bars were tested in bending. In the former, the effect of reducing the shear stirrups spacing was analyzed together with the under- and over-reinforcement at the central support and midspan cross-sections, respectively. The development of a crack hinge in the continuity support zone highlighted the better performance of beams under-reinforced on the top layer with GFRP bars compared to “equivalent” beams reinforced with steel, namely at the resistance level. In addition, the confinement at critical zones increased significantly the strength and ductility. The numerical investigations included the development of non-linear finite element models for all beams tested - numerical results are in good agreement with test data and seem to confirm the confinement effect observed in the experiments.     

Glulam beams reinforced with FRP externally-bonded: theoretical and experimental evaluation

The glued- laminated lumber (glulam) technique is an efficient process for the rational use of wood. Fiber-reinforced polymer (FRPs) associated with glulam beams provide significant improvements in strength and stiffness and alter the failure mode of these structural elements. In this context, this paper presents guidance for glulam beam production, an experimental analysis of glulam beams made of Pinus caribea var. hondurensis species without and with externally-bonded FRP and theoretical models to evaluate reinforced glulam beams (bending strength and stiffness). Concerning the bending strength of the beams, this paper aims only to analyze the limit state of ultimate strength in compression and tension. A specific disposal was used in order to avoid lateral buckling, once the tested beams have a higher ratio height-to-width. The results indicate the need of production control so as to guarantee a higher efficiency of the glulam beams. The FRP introduced in the tensile section of glulam beams resulted in improvements on their bending strength and stiffness due to the reinforcement thickness increase. During the beams testing, two failure stages were observed. The first was a tensile failure on the sheet positioned under the reinforcement layer, while the second occurred as a result of a preliminary compression yielding on the upper side of the lumber, followed by both a shear failure on the fiber-lumber interface and a tensile failure in wood. The model shows a good correlation between the experimental and estimated results.