Structural Behaviours Of PPR-CFFT Column And Joint For Ocean Construction

In the present thesis,an innovative fiber reinforced polymer(FRP)-concrete hybrid structure is proposed aiming at the great demand of ocean development and construction.The proposed hybrid structure system has the advantages of high corrosion-resistance,low maintenance requirements,permission to use marine local materials and ease of installation,and thus has a great application potential in ocean construction.The present study investigates the mechanical behaviors of the two key components in this hybrid structure system,i.e.the column and joint.Firstly,a pultruded profile-reinforced concrete-filled FRP tube(PPR-CFFT)column is proposed.This new column consists of a concrete-filled filament-wound FRP tube(CFFT)longitudinally reinforced with pultruded FRP profiles.A series of concentric compression,eccentric compression and four-point bending tests were conducted on PPR-CFFT columns,and their typical failure modes under various loading scenarios were obtained.The test results showed that the mechanical properties of PPR-CFFT columns were superior to the reference CFFT columns under combined compression and bending,which can be attributed to: 1)the embedded pultruded profiles significantly improving the flexural strength and stiffness;2)the slotting configuration on the pultruded profiles effectively preventing the slippage between the pultruded profiles and concrete.This enables the strength of the pultruded profiles to be fully developed,and consequently the columns exhibited stable load-carrying capacity and stronger deformability.Afterwards,a progressive damage constitutive model for FRP was extended,and a finite-element analysis(FEA)model was developed for PPR-CFFT columns.Through a full range analysis on the behaviors of PPR-CFFT columns under concentric and eccentric compression,the mechanism and influence of non-uniform confinement of the FRP tubes were revealed.Based on the experiments and numerical simulation,a detailed section analysis was established for PPR-CFFT columns,and the influences of the parameters on the load-carrying capacity were analyzed.Moreover,a section analysis program capable of considering the change of bending direction was further developed,and a comparative study on the performance of PPR-CFFT columns under varying biaxial bending and axial load was conducted.Finally,a design method was proposed for PPR-CFFT columns under combined compression and bending.Secondly,a configuration of the joint between PPR-CFFT column and pultruded FRP beam was invented.Experiments were conducted on the joints with constant load on the column and symmetric or antisymmetric loading at the end of the beams.The obtained typical failure modes were always the local buckling of the compressed flange of the pultruded FRP beam near the joint.Until failure,the joints exhibited stable load-carrying capacity and high bending stiffness,and can be classified as a rigid connection.The performance degradation and load transfer mechanism of the joints were analyzed,and a calculation method for the load-carrying capacity was proposed.Then experiments and numerical simulation were carried out on axial compression performance of the joints.The results indicated that the joint zone can provide sufficient axial load-carrying capacity.Through parameter analysis with the FEA model,the key parameters affecting the axial compression performance of the joints were identified.Finally,the axial compressive behavior of seawater coral aggregate concrete(SCAC)-filled FRP tubes was investigated.Test results indicated that packaging with FRP tubes can prevent the brittle failure of SCAC under compression,and the following confinement effect exhibited strength and deformation enhancements for SCAC.In experiments,SCAC was further found to have volume compressibility,and the resulting “compacting effect” led to the confinement of FRP tube on SCAC being delayed.Based on this,an extended model considering the “compacting effect”,which can predict the behavior of FRP-confined-SCAC under axial compression,was developed on the basis of existing models.Above,this thesis can provide theoretical foundation and technical support for the engineering application of the FRP-concrete hybrid structures.