Study On Monitoring Technique And Damage Evolution Method Of Ancient Timber Structure Considering The Long-term Environment Effect And Seismic Effect

Ancient timber structures are important cultural relics and precious historical heritage in China.With the impact of long-term environment corrosion,human action and cumulative seismic effect,the deformation and damage extent is increasing year by year for ancient wood structure,even collapse at last.By constructing a SHM system before the structural failure,revealing the damage mechanism during the natural service,and assessing on the damage based on the monitoring data,it is beneficial for managers to fully know the security state and damage process and to better achieve maintaining and repairing of ancient timber structure.However a large number of deformation monitoring technologies have some problems such as implement monitoring,complex date intergration and processing,high price for mass monitoring.Meanwhile the study on ancient timber structure is mainly focus on the mechanical properties.The investigations of damage evolution process and damage assessment of ancient wooden structures under environmental or seismic effect have some problems such as incomplete nfluencing factors and damage evolution methods.In view of this,firstly a deformation monitoring method based on fiber brag grating(FBG)strain measurement was proposed in this thesis,which can obtain the deformation values in state monitoring for longtime.Secondly a constitutive equation of wood considering the thermal cycling with humidity by using FEM software further-development is deduced to conduct the damage evolution of ancient timber structure based on the monitored data.A multi-scale seismic damage evolution analysis method for the ancient timber structure was also presented to study the damage evolution process and assess the damage extent of ancient timber structure under seismic effect.Finally,based on an ancient timber building in service as project background,the proposed methods are applied into SHM system of a ancient timber building and the damage evolution and real-time monitoring of the ancient timber building can be realized.The main research works are as follows:(1)The deformation monitoring research of ancient timber structure based on FBG technology was conducted in this paper to provide the data support for monitoring system and damage evolution.Considering the character of ancient timber structure,the deformation monitoring method of beam deflection and column inclination can be derived based on geometrical trigonometric function relationship and polynomial fitting method.The deformation values of multiple components can be obtained by using single sensor technology.Through finite element analysis and theorical analysis,the proposed deformation monitoring method shows a good applicability on monitoring the deformation of ancient timber structure.A statistic test of timber beam and a capsizing test of timber column are conducted in laboratory to verify the effect of the proposed monitoring method,The results show that the proposed monitoring approach has a high precise and good applicability in traditional ancient timber structure monitoring.(2)A damage evolution simulation method of ancient timber structure was conducted by considering thermal cycling with humidity effect.Firstly some old ancient wood removed from an in-situ ancient timber structure were manufactured as wood specimens and conducted the material properties test.The degreation law of and the properties of old wood can be obtianed from the test.Based on the test result,the elastoplastic constitutive model of wood considering the effects of normal creep and mechanical adsorption creep of wood are deduced under the effect of temperature and humidity.Then the elastoplastic constitutive equation is incorporated into finite element software ABAQUS user subroutine UMAT.The damage evolution simulation of structure can be realized under the change of temperature and humidity.At last the effectiveness of the proposed constitutive model was verified by comparing with the results of finite element simulation and the test results.The proposed constitutive model and simulation method can provide a FEM tool for damage evolution of ancient timber structure under humidity and temperature changes.(3)A multi-scale seismic damage evolution analysis method for the ancient timber structure was presented to reveal the damage evolution process and assess the damage extent.Firstly according to multiple point constraint method,the deformation at the interface between structural macroscopic models and local microscopic models are compatible well with each other.The multiple-scale model of ancient timber structures can be established with good computational efficiency to investigate the mechanical property of whole structure and local failure details.Secondly in accordance with generalized force-deformation relation,the generalized damage index is established and then to be normalization based on test data and performance-based seismic design.At last the multi-scale consistency damage index is proposed on the basis of the previous analysis.The proposed damage index for ancient timber structures are validated through mortise-tenon joint under cyclic loading test.A three-story timber framework simulation models is also chosen as analytic target in this paper to research the damage evolution process and damage mechanism of the ancient timber structure under infrequent earthquake.The research result shows that the multi-scale consistency damage index proposed in this paper have a good effect on devealing the damage mechanism in each scale leverl and evaluating the damage of ancient timber structure under seismic effect.(4)An ancient timber building in service "Qijia residential building" was regard as a project background to install the SHM system.The damage evolution research of"Qijia residential building" was also conducted in this thesis.Based on the in-suite test and collected data,the effectiveness of SHM system and the proposed deformation monitoring method can be verified.The service status of "Qijia building"was also assessed based on finite element analysis.The temperature and moisture function can be derived from fitting the collected data from SHM system.Combing with the proposed damage evolution method and the temperature and humidity function,the strain distribution and the deformation of longue frame in "Qijia building" were obtained over the next 50 years considering the humidity and temperature cycling.Through comparing with the monitored data from SHM system and the results of scene investigation,the damage evolution results can be verified and show good effects on revealing the damage developing trend and assessing the damage extent of ancient timber structure.After the model physical parameters of"Qijia residential building" had been obtained by the collected data and the model updating,the multi-scale finite element model of "Qijia residential building" was established to study the damage evolution process of the structure under rare earthquake.Therefore the damage mechanism and evolution process can be revealed for ancient timber structures in north of Fujian Province;furthermore the damge extent can be assessed.