Experimental Study And Theoretical Analysis On Strengthening For Chinese Ancient Timber Buildings

Chinese ancient timber buildings(CATB)system is a unique building system in the world ancient buildings with high historical,cultural relic,artistic and scientific value.It is very important to study the strengthening of CATB for protecting those precious historical relics.The design reference period for repairing of ancient buildings is presented,and the calculation methods of actions are analyzed.The design strength of ancient wood should obtain from measured strength in terms of the law of development of the ancient wood property,and the method for design strength is proposed.The position of bearing point is got according to the equal angle of rotation between purlin and Queti,thus its maximum internal force can be obtained.The force of the Sanjiao beam is calculated through simplification the load distribution between the Sanjiao beam and Queti to triangular distribution.The dynamic equation of single-degree-of-freedom system with glide lamella simplified from palace timber structure is established according to the characteristic of that structure,and numerical calculation method of the equation is given using step-by-step integration.According to the static tests of 8 rectangular timber beams strengthened with carbon fiber reinforced polymer(CFRP)sheets,the bending behaviors are studied such as failure characteristics,strain of timber section,ultimate beating capacity and deformation.Formula for flexural capacity is established considering initial strain or not based on different failure models.Approximate calculation method of deflection is presented,in which the load-deflection curve of timber beams is simplified to bi-linearly. The factors influencing on the flexural capacity of timber beam strengthened with CFRP sheets are analyzed using that formula.The distribution of interfacial bond shear stress at the end of CFRP sheets was obtained based on above tests,formulae for calculating interracial bond shear stress and bond normal stress between the CFRP sheet and the timber beam are deduced,the main factors influencing on the maximum interfacial bond stress are analyzed using the formula,and the calculation method of anchorage length for CFRP sheet is presented according to the tensile force of CFRP sheet.According to the experimental study on shear property of 7 rectangular timber beams strengthened with CFRP sheets,the shear behaviors are obtained such as failure patterns,load-deflection curve and load-strain relationship.The judgment condition of failure pattern is presented based on theoretical analysis,the calculation method of shear capacity is established,and the influencing factors are analyzed.Based on the experimental investigation on timber column strengthened with CFRP sheets,the mechanical properties are obtained such as failure modes,load-strain relationships of timber columns and CFRP sheets,the ultimate capacity and its influences on strengthened columns.The maximum intercept height,the miminum connecting length of an intercept timber column and the bearing capacity of the lock ring are proposed according to the mechanical analysis on that intercept column.The low-cyclic reversed loading tests were conducted on 8 wooden frame models, including 3 unreinforced models made in accordance with the requirements of the Fabrication Methods of Song Dynasty(960-1270,A.D.),3 models strengthened with carbon CFRP sheets,and 2 models strengthened with flat steel.Such behaviors as the failure characteristics,hysteretic curve and skeleton curve,degeneration of strength and rigidity,deformation and energy dissipation capacity are analyzed.Restoring force model is established based on this experiment,and that of prototype structure is obtained. Displacement-based seismic strengthening method is put forward according to the existing seismic code,and the influence of rigidity on building is analyzed.Based on the shear bond experiment between wood and CFRP sheet,the bond properties are researched such as failure character,characteristic of strain distribution, effective bond length and bond strength.