Experimental Investigation On Axial Compression Behavior Of GLT And CLT Columns Confined With FRP Sheets

Glue-Laminated Timber(GLT)and Cross-laminated timber(CLT),as new engineering wood products,have been concerned by many researchers for their good mechanical properties.Fiber reinforced polymer(FRP)has the advantages of light weight,high strength,fatigue resistance and corrosion resistance.The mechanical properties and durability of wood structures restrained by FRP can be effectively improved.At present,there are many researches on FRP reinforced wood structures,but few researches on FRP reinforced CLT and GLT members.In order to promote the application of CLT and GLT in civil engineering,the monotone and repeated loading tests of CLT and GLT columns confined with FRP are carried out in this paper.The effects of FRP types and layers on the mechanical properties of GLT and CLT short columns were studied by analyzing the experimental phenomena and data.The restraint mechanism of FRP was explored and the ultimate strength model was established.The main research contents are as follows:(1)The effects of types of FRP and number of FRP layers on the compressive properties of CLT columns and GLT columns were studied by monotone loading tests.It was found that after wrapping FRP,the ultimate load increased by 6.35～36.19%,the elastic modulus increased by8.09～33.76%,the ductility increased by 25.27～80.95%,and the Poisson’s ratio decreased by11.48～54.1%.The restraint effect of two-layer FRP is better than that of first-layer FRP.Comprehensive analysis shows that CFRP had a better constraint effect than BFRP,and CFRP had a more significant advantage when wrapping two-layer FRP.(2)The existing strength models of concrete columns confined with FRP and wood columns confined with FRP were summarized,and the strength models for CLT columns and GLT columns confined with FRP were proposed.Compare the three model values with the experimental values,the suitability of the model was assessed.The results show that the proposed strength model can predict the ultimate compressive strength of CLT columns and GLT columns confined with FRP.Based on the pervious mechanical model of concrete columns confined with FRP proposed,the mechanical constraint model for CLT columns and GLT columns was established.The fitting analysis between the model value and the experimental value showed that the calculated value of the constraint model was consistent with the experimental value.(3)The effects of types of FRP and number of FRP layers on the axial compression performance of CLT columns and GLT columns confined with FRP under repeated loading were studied.The result showed that the failure modes of specimens are basically consistent with that of monotonic loading tests.Under repeated loads,the ultimate load and initial stiffness of specimens wrapped with FRP were increased by 11.15～35.72% and 10.54～56.01% respectively.The ultimate load of the two-layer FRP restrained columns was 1.65～13.42% higher than that of the first-layer FRP restrained columns,and the initial stiffness of the two-layer FRP restrained columns was1.92～42.39% higher than that of the first-layer FRP restrained columns.The hysteretic curves of unconstrained specimens were sparse,while those of FRP constrained specimens were fuller.The trend of skeleton curves of specimens was similar,while the ultimate load and ultimate displacement of specimens confined by FRP were significantly increased.The stiffness degradation curves of each group of specimens had roughly the same trend.With the increase of the displacement,the stiffness of specimens and the decreasing range of stiffness decreased gradually.Compared with the unconstrained specimens,the initial stiffness of the FRP wrapped specimens increased obviously,and the stiffness degradation amplitude decreased obviously.By comprehensive comparison,the initial stiffness of CFRP constrained column was the highest,and the stiffness degradation amplitude was the slowest.