Study On Bending Behavior And Damage Warning Of GFRP-Concrete Composite Beams

Lightweight,high tensile strength and fatigue resistance represents the trend of development in modern bridge engineering.Fiber-Reinforced Polymer(FRP)has been widely used in bridge engineering because of its high strength,good durability and other excellent characteristics.However,FRP is also subject to some limitations in its application due to its brittle failure characteristics.To overcome this problem and make the best use of such materials,the combinations of FRP and other materials have recently been investigated by some researchers.In this study,we designed a glass fiber I-beam and six GFRP-concrete composite beams jointed by different bolts on the basis of previous domestic and international studies.Bending performance,damage early-warning,parameter optimization of GFRP-concrete composite beams were studied.The main experimental results and findings are summarized as below.1.The four-point bending test was carried out for seven beams.We investigated the influence of load-deflection curve,load-strain relationship,and bolt diameter on the bearing capacity of composite beams,and the influence of concrete height on the stiffness of composite beams.Using of the GFRP composite materials and concrete can greatly enhance the structural capacity.For the test cases,the bolt volume ratio around 1%is appropriate,which reasonably coordinates the deformations between the GFRP I-beams and concrete.The height ratio between the concrete beam and GFRP I-beam should be controlled within a reasonable range to prevent the brittle damage of composite beams.2.The whole loading process for seven testing beams was monitored by an acoustic emission(AE)device.The phase space of the loading process was reconstructed based on fractal theory,and the correlation dimension of AE energy signals for each individual loading stage was then calculated by Matlab.We found that the correlation dimension of AE energy signal can well describe the development of damage and the final failure during the whole process of loading.It is recommended that the AE sensors be arranged in the area of larger shear for the GFRP-concrete composite structures,and the warning point of damage can therefore be determined when there is persistent fluctuation of high amplitude of fractal dimension.In this case the bearing capacity of the structure may reach 70%of the maximum,and much more intense monitoring and structure reinforcement is required.3.The finite element simulation of GFRP-concrete composite beams was established by ANSYS.The validity of the model was verified by the experimental data.Then,the model was used for numerical analysis of GFRP-concrete composite beams.The simulation indicates that the grade of FRP should be matched with the strength of concrete in order to effectively use the two materials.The optimized shear deflection coefficient of I-shaped GFRP-concrete composite web is safer for structure design.The height ratio of concrete and GFRP cross-section is reasonable within the range of 0.33 to 0.58.In this paper,the reasonable ratio of bolt volume,method of damage warning and optimization of cross section design of GFRP-concrete composite beams are researched,which provides some reference for the popularization and application of GFRP-concrete composite beams.