| After thousands of years of development and evolution,the Chinese historic timber structure has become a valuable heritage of architectural art in China and even in the world.In the historic timber structure,timber column may experience local damage(insect attacks and fungal decay)due to the defects of wood properties under the action of external factors(pest invasion and wind and rain erosion).That seriously affects the bearing capacity of the timber column and is not conducive to the load resistance of the whole timber structure.Therefore,it is of great significance to explore the degradation rule of the mechanical properties of locally damaged timber columns and their retrofitting techniques.In this paper,the compressive properties of locally damaged timber columns were studied through experimental research and numerical simulation analysis,and the compressive properties of composite retrofitting timber columns were also studied through axial compression test.The degradation rule of damaged timber columns and the recovery effect of different retrofitting techniques were analyzed,and the theoretical model of the ultimate loadcarrying capacity of damaged timber column under axial compression was established.The main contents of the work are listed as below:(1)The impacts of different damage conditions on the compression behavior of timber columns were revealed.A total of 10 intermediate slender columns including the intact column in four groups with different damaged conditions were tested under axial compression.Damaged areas,damaged positions and damaged forms of the columns were considered.The failure modes and mechanical properties of all damaged timber columns were discussed,and their ultimate load-carrying capacity,stiffness,ductility were compared.(2)The composite retrofitting techniques for locally damaged columns using the combination of wood block,angle steel and carbon fiber reinforced polymer(CFRP)wrap and the combination of wood block,GFRP profile and CFRP wrap were proposed,compared with the traditional methods of using wood block only,and both wood block and CFRP wrap.The compressive performances and recovery effect among these 4 retrofitting techniques for the columns damaged at 1/2 column height had been compared based on the failure mode and ultimate load-carrying capacity stiffness and ductility by the axial compression test.(3)Parametric analysis was carried out.The numerical simulation analyses of the finite element models for locally damaged columns were conducted by ABAQUS finite element program.The correctness of the finite element model was validated by comparing the results of finite element analysis with experimental results.On this basis,a further analysis was conducted on the degradation pattern of the load-bearing capacity of timber columns due to factors such as the damaged area,damaged length,and damaged position.(4)The verification formulas for the bearing capacity calculation of eccentrically compressed timber columns in current timber design codes were discussed.Based on the loadcarrying mechanism and deformation characteristics of damaged timber columns,the calculation model of ultimate load-carrying capacity for unilaterally damaged timber columns was proposed,considering material nonlinearity,geometric nonlinearity and 2nd order effect of member.The theoretical model agrees well with the finite element simulation results. |
