Research On The Mechanical Performance Of The Roof Structure Of The Palace-style Ancient Buildings

Chinese ancient wooden buildings are known for their unique architectural styles,beautiful artistic modellings and excellent structural systems,especially the palaces and temples.Their far-reaching eaves and slightly uplifted roof corners are very oriental,which are major features of ancient Chinese architecture different from Western ancient architecture.Under the guidance of “Enhancing cultural self-confidence and carrying forward the national spirit”,it is of great and far-reaching scientific significance and social value to research and protect ancient wooden buildings in China.As a typical feature of the palace-style ancient architecture in China,the roof structure has not received enough attention in terms of mechanical properties,and the protection work lacks scientific guidance.Therefore,this paper has carried out research on the mechanical properties of the temple-type roof system.This paper took the temple-style roof structure system as the main object,analyzed and summarized its main structural features and roof construction techniques in the Tang,Song,Ming and Qing Dynasty.Afterwards,the representative main hall of Kaishan Temple was taken as the prototype,whose depth,width and cross-section dimensions of the rafters,king posts,oblique beams and purlins were obtained.The third-class palace-style roof structure system was designed,which laid the foundation for subsequent mechanical analysis.The mortise-tenon joint solid models were established for unidirectional loading calculation and analysis since the correctness of the modeling analysis methods and parameter selections had been verified by comparison with the experimental results.After a full-scale finite element solid model of one-story beams composed of 3-purlin beam and 5-purlin beam was established,the deformation of beams under plane and out-of-plane loads was obtained.The strain and stress of the joint region show that the Mantou mortise-tenon joint is more deformed than the Zhi mortise-tenon joint,and Mantou mortise-tenon joint is more prone to plucking damage.According to the simulation results,the hysteresis curves and skeleton curves of the beams under plane and out-of-plane loads were plotted,and the eigenvalues such as lateral stiffness,yield bending moment and ultimate bending moment were analyzed.The angular displacement formula of beam with semi-rigid nodes at both ends was derived.Then a finite element model of the truss was established,and the internal forces of beams under the action of gravity and wind were calculated.The results show that both side segments of rafters are subject to larger bending moment and shear force,which are the key parts of the rafters.Besides,the Chashou and Tuojiao have a greater reduction on the internal forces of the beams.The finite element model of the roof structure was established,and the stress and displacement under the action of gravity and wind were calculated.The results show that the stress and displacement of the lower purlins at the center and the middle purlin on the side of gable,which are weak members,are larger.In addition,the rafters and king posts have less stress.The effects of roof mass,folding,building’s width and depth on the stress and deformation of the roof structure were studied.Based on the dynamic characteristics of the roof beam system,the appropriate seismic waves were selected,and the dynamic response calculations of the roof structure were carried out.Furthermore,the acceleration,displacement and stress of the key components were analyzed,which show that the acceleration and displacement peaks of each rafter increase with the enhancement of seismic load,and the energy dissipation of the Dougong brackets and tenon-mortise joints becomes more.Besides,the horizontal displacement of the structure mainly occurs in the layer of Dougong bracket,and the relative displacement between each rafter is small.Moreover,the beam components are still in elastic state as a whole under severe earthquake.Finally,the effects of roof mass,folding and parallel elastic modulus of wood on dynamic response were analyzed.