| The ancestral hall in Canton is a kind of building system which is between the senior palace and common house.As a result of the long-term erosion of the external environment,there are a large number of ancestral hall buildings were damaged to varying degrees and they are in urgent need of protection and repair.The hoop tenon-mortise joints are often used to connect the beams and columns in ancestral hall.The detail of the hoop tenon-mortise joints has obvious regional characteristics,but until now,the researches on strengthened damaged hoop tenon-mortise joint of ancestral halls in Canton are insufficient,which brings great difficulties to the protection and repair of the ancestral hall in Canton.Study on the seismic behavior of the strengthened damaged hoop tenon-mortise joints has both theoretical significance and economic benefit.The following research works were carried out in this paper.(1)Fourteen bond-slip specimens of Carbon Fiber Reinforced Polymer(CFRP)-timber are tested to explore the effects of different bonded length,different CFRP layers and different CFRP hoop layers on bond-slip.The results show that,when the number of CFRP layers is small,the ultimate bearing capacity of the specimens increases with the increase of the number of CFRP layers,while the bond surface failure occurs when the number of CFRP layers is more.Interface striping between CFRP and timber is a process of bonded shear stress transmission from the loading end to free end,and the local slip along the CFRP from the loading end to free end is a process of nonlinear change from large to small and its effective bonded length between CFRP and timber is 180 mm to 200 mm.The effect of hoop on the ultimate bearing capacity of the specimen is not obvious,but it will affect the strain transfer of CFRP.The more the number of hoop layers has,the stronger the constraints are.(2)Seven hoop tenon-mortise joints that had been damaged in seismic test are strengthened,and low-cycle reversed loading tests of them are carried out.The seismic behavior of joints before and after strengthening is compared,and the influence of parameters such as column diameter D,tenon width t and different strengthening methods on the seismic behavior of joints is discussed.Experimental results show that the bearing capacity of four specimens after strengthening is larger than that before strengthening and the initial stiffness of the strengthened specimen is obviously greater than that before strengthening.The ultimate bending moment of CFRP strengthened joints is mainly affected by the original damage degree of beam tenon,and the ultimate bearing capacity of the specimen strengthened by steel sleeve is significantly higher than that before strengthening.In addition,the initial rotational stiffness of strengthened damaged hoop tenon-mortise joints increases with the increase of column diameter D and tenon width t,and the ultimate bending moment and energy dissipation capacity of the joints are positively correlated with the section modulus in bending of the strengthened beam.In general,the seismic behavior of the joint strengthened by steel sleeve is the best,followed by the CFRP strengthening method without restricting the tenon rotation,while the glue-injecting L-type CFRP strengthening method with restricting the tenon rotation is the worst.(3)Based on the analysis of the mechanism of strengthened damaged hoop tenon-mortise joints,the theoretical relationship between bending moment and rotational angle on strengthening joint,including strengthening method of CFRP-M1 and CFRP-M2,is deduced,and the correctness of the theoretical formulas is verified by the experimental results.Based on the analysis of the factors that affect the relationship between bending moment and rotation angle of strengthened damaged hoop tenon-mortise joints,it is found that,for two strengthening methods,the initial stiffness of the strengthened damaged hoop tenon-mortise joints,the critical fracture moment of CFRP on the side of the beam and the critical fracture moment of L-shaped CFRP increase with the increase of the height h of the beam,the diameter D of the column,and the width t of the tenon.The critical fracture moment of CFRP on the side of the beam increases first and then decreases with the increase of layer of CFRP on the side of the beam.The ultimate bending moment of the strengthened damaged hoop tenon-mortise joints is related to the original damage crack depth of the beam tenon,the conversion thickness of the upper and lower CFRP of the beam,the beam height h,the column diameter D,and the tenon width t and so on.The theoretical calculation formula is simplified and the mechanical calculation models of triple-lines and five-lines are put forward according to different stress characteristic points of strengthened damaged hoop tenon-mortise joints. |
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