Study On Static Performance Of Ancient Timber Frame Under The Combined Action Of Load And Environment

The main load-bearing structure of the ancient wooden building is wooden frame.Mortise-tenon joints connections are widely adopted to combine structural members.Wood is a porous and hygroscopic biological material,easily affected by the change of temperature and humidity in the surrounding environment.In the case of changes in temperature and humidity,the wood will be greater internal hygrothermal stress.Under load and the change of environment temperature and humidity,wooden structure will appear normal creep and mechanical adsorption creep phenomenon,which makes wooden structure appear complex stress and deformation.The service life of ancient wooden structure is generally long,so ancient wooden structure is subjected to the action of load and environment for a long time,which is bound to affect the bearing capacity of the ancient wooden structure,and ultimately will affect the normal use and safety and reliability of the ancient wooden structure.In this thesis,the static performance of ancient timber frame under the combined action of load and environment is studied.The main research work and results are as follows:(1)Ancient wood was selected and manufactured wood specimens and conducted the material properties experiment of wood and adsorption creep experiment of an ancient bending beam.Wood mechanical adsorption creep rules were obtained by beam bending mechanical adsorption creep experiment.Experimental results show that the wood beam mid-span deflection fluctuates with changes of relative humidity in environment.When the environment relative humidity decreases,the mid-span deflection of beam increased.When the environment relative humidity rises,the mid-span deflection of beam decreased.Beams under load and environmental changes of temperature and humidity in interaction,its mid-span deflection showed an upward trend;and by setting the control experiment,we found that the mid-span deflection amplitude of smaller size beams is larger than the size of timber larger,mechanical adsorption phenomenon more obvious.(2)Considering the effects of normal creep and mechanical adsorption creep of wood,the Tsai-Wu criterion is chosen as the wood yield criterion,and then the elastoplastic constitutive equation of wood is deduced under the changes of temperature and humidity.Incorporating the elastoplastic constitutive equation into the finite element software ABAQUS user subroutine UMAT realize the finite element analysis of ancient wooden structure under combined action of load and the change of temperature and humidity.The results of finite element simulation are compared with the experimental results,which verify the correctness of the constitutive model.(3)Using finite element software ABAQUS established dovetail mortise-tenon joints wooden frame and through mortise-tenon wooden frame of short-term changes in temperature and humidity model and long-term changes in temperature and humidity models.Calculation and analysis show that under the combined action of short-term load and the change of environment temperature and humidity cause a greater horizontal stress in the wooden frame.Under the combined action of long-term load and the change of environment temperature and humidity,the mid-span deflection of two types of wooden frame architrave will be increased with time,causing structural damage to the wooden frame.MATLAB software is used to fit the mid-span deflection curve of ancient wooden frame architrave,and the calculation formula is proposed for the ancient wooden frame architrave under the action of load and temperature and humidity changes.