Structural Condition Assessment For Large-scale Towering Ancient Wooden Buildings

Large-scale towering ancient wooden building is an important part of ancient architecture in China,with high historical,scientific,and cultural value.However,large-scale towering ancient wooden buildings have been damaged by natural aging,earthquake,wind disaster,war,etc.for hundreds of years,resulting in different levels of damage and destruction.That significantly reduces the anti-risk capacity of the structure.In order to delay the decline and fall of large-scale towering ancient wooden buildings,it is necessary to analyze and assess the structural state of large-scale towering ancient wooden buildings under self-load,earthquake,and strong wind.Therefore,the large-scale towering ancient wooden building was selected as the research object.The Sakyamuni Pagoda of Fogong Temple,the typical large-scale towering ancient wooden building,was selected as a case study.The model experiment and numerical simulation methods were used to study the structural characteristics of large-scale towering ancient wooden building structures,simplified simulation method of dougong and mortise &tenon,finite element model modeling and modification,distribution rule and calculation of external load and structural state evaluation method were presented.The research results provide an important foundation and support for the sustainable preservation,protection,and utilization of large-scale towering ancient wooden buildings.The main research contents and conclusions are as follows:(1)The main structural types,structural characteristics,development process,geographical environment,and geological conditions of large-scale towering ancient wooden buildings were systematically studied.The research results show that the main characteristics of the large-scale towering ancient wooden building are the tall appearance,the pursuit of a kind of rising,dynamic,spiritual space effect,the interior has a high space for people to move,the frame structure as the main bearing system.The existing large-scale towering ancient wooden buildings have occurred material deterioration,component damage,and structural inclination.They mostly are in the earthquake zone and subjected by the strong wind load.The anti-risk capacities of the existing large-scale towering ancient wooden buildings are relatively weak.(2)A simplified simulation method of dougong based on multiple plastic element and a shear plastic hinge was proposed,as well as a mortise-tenon joint simulation method based on the flexural plastic hinge.The types of dougong and mortise-tenon are introduced in detail and their hysteresis performance was analyzed.The finite element models of dougong and mortisetenon were established by simplified simulation method,and validated by comprehensive comparison test.The results show that the simplified simulation method for dougong and mortise-tenon can accurately and reliably simulate the hysteresis performance of dougong and mortise-tenon,with an average difference of about 10%.(3)The finite element modeling strategies and model updating methods of large-scale towering ancient wooden buildings were proposed.The requirements of the finite element model for structural state assessment of large-scale towering ancient wooden buildings were clarified.A finite element modeling strategy suitable for large-scale towering ancient wooden buildings and a simplified model modification method based on multiple degrees of freedom considering the initial inclination of the structure were proposed.The finite element model establishment and modification of Yingxian wooden pagoda were carried out,and the results were compared with the field monitoring.The results show that the proposed finite element modeling and updating method can effectively improve the model accuracy of Yingxian wooden pagoda.The structural natural period difference decreases from 10% to 3%,and the modal MAC increases from 0.7 to 0.9.(4)The wind tunnel test of large-scale towering ancient wooden buildings was carried out.The wind tunnel test on the Yingxian wooden pagoda of 1:50 rigid pressure measurement model was carried out to study the wind pressure and wind load distribution of the wooden pagoda,and compared with the wind load in field monitoring.The results show that the maximum average wind pressure coefficient appears on the middle and upper part on the windward side of the wooden pagoda.The wind pressure changes from pressure to suction on the side windward side,and the crosswind side and leeward side occur a large wind suction.The whole roof is subjected to wind suction.The wind loads calculated by the wind tunnel test are similar to those of the field monitoring,with a difference of less than 20%.(5)The computational fluid dynamics(CFD)numerical simulation process and method of the large-scale towering ancient wooden buildings were proposed.Four different turbulence models of Yingxian wooden pagoda were numerically simulated to study the effects of different turbulence models on wind pressure distribution.Furthermore,four CFD geometric models with different accuracy were investigated to study the influence of roof ridge,outer column,dougongs,and railings on the wind flow field.The results show that Realizable k-ε turbulence model can accurately predict the wind pressure distribution on the windward,crosswind,and leeward sides of the wooden pagoda,with a relative difference of about 18%.The higher accuracy of the CFD geometric model,the more accurate the prediction of wind pressure.The components that have a great influence on the architectural appearance will affect the calculation accuracy.The body shape coefficients of the Yingxian wooden pagoda are similar to those of modern buildings only on the windward surface of the bright floor.(6)The method of structural state assessment of the large-scale towering ancient wooden buildings was proposed.A multi-objective and multi-level analysis method for the state assessment of large-scale towering ancient wooden buildings was proposed based on the key parameters of the state assessment of ancient wooden buildings.The definition of the limit state of the method and its applicable scope were also studied.The structural states of Yingxian wooden pagoda under the actual situation,self-inclination,earthquake,and strong wind were assessed.The development law and failure mode of the wooden pagoda was investigated.The results show that the Yingxian wooden pagoda has reached a state of mild damage and the individual components of the second floor flat floor and bright floor have produced very serious damage.The final failure mode of the wooden pagoda under its own incline action is as follows:the incline displacement increases,resulting in damage degradation of component members and the reduction of bearing capacity.In addition,the influence of the second-order effect of structural gravity(P-Δ)finally leads to the local instability of the second flat and bright floor,which leads to the loss of bearing capacity of the structure.The wooden pagoda has mild damage and severe damage respectively under frequent and rare earthquakes,while dougong and mortise-tenon component has a certain amount of medium damage.The damage of the wooden pagoda is relatively small under extreme wind actions.The pagoda achieves mild damage and has a good bearing capacity.Under normal wind load,the wind-induced vibration of the wooden pagoda is small,and its range is at an excellent level.