Compressive Behaviour Of Annular Section Glass Fiber-Reinforced Polymer(GFRP)-Concrete Columns

Tubular piles are often utilized as foundations or supports for the marine front structures,such as trestles,wharves and mooring platforms.Apart from resisting the combination of vertical and horizontal loads,these piles are also faced with the durability problem caused by steel corrosion in harsh marine environment.Fiber-Reinforced Polymer(FRP for short),due to its excellent mechanical properties and well corrosion resistance,can substitute for steel in such cases,so that FRP-concrete composite structure becomes an ideal structural form to meet the requirements of this kind of tubular pile.Based on existing applications of FRP material in concrete structures,a hybrid GFRP-concrete composite structural component has been proposed in the present study.It consists of three components: the hollow concrete column,external GFRP tube and internal GFRP longitudinal reinforcement.The slender column of this component can be used as the hybrid tubular pile to meet the marine environment's requirements.In order to understand the mechanical properties of this component under the axial compression or the coupling of bending and compression,the author has carried out systematic experimental research program and analysis by a series of shout column specimens:(1)Axial compression tests were carried out to investigate the effects of the position of the longitudinal bars,the reinforcement ratio and the configuration of concrete cross-section as well as the strength of GFRP confinement on the performance of the pile's axial compression behavior.In the first batch of tests,it was found that the placement of longitudinal bars against the tube had a negative impact on the performance of the pile,and then in the second batch of tests,the cross-section design of the piles was improved.The results show that the pile has a bilinear load-displacement behavior with stable increasing of load-bearing capacity after yielding.The ultimate load-bearing capacity and ductility of the pile perform well.GFRP bars have made a major contribution to its compressive performance.(2)In addition,the author has compared the stress-strain relation of FRPconfined concrete with circular cross-section and with annular cross-section with a void ratio of 0.5.Based on the theoretical model for FRP-confined concrete model proposed by Teng J.G.et.al.,a series of improvements are made through theoretical analysis and experimental results.After that,some semi-empirical formula have been derived and a FRP-confined concrete constitutive model suitable for annular sections is obtained.(3)Tests were carried out to investigate the mechanical properties of the pile with the eccentricity of 25 mm and 50 mm,respectively,and another two four-point bending tests were also conducted.The results indicate that with the increment of eccentricity,the axial bearing capacity decreases and the lateral deformation increases.According to the experimental strain data,the change of FRP confinement performance under eccentric compression is discussed.Then using the modified concrete constitutive relation and the small strip method,a nonlinear analytical model for short columns has been established to predict load-lateral displacement curves and the M-N curves of the pile.At last,the results were compared with the experimental data and were analyzed.