ANALYSIS OF MECHANICAL PROBLEMS OF TAI-HE PALACE IN THE FORBIDDEN CITY BEFORE RENOVATION

摘要

Before renovation of Tai-he Palace in the Forbidden City,it was found during survey that some mechanical problems occurred on its wooden members,which included:(1)deflection of middle part of its western eave purlin was overlarge;(2)sinkage of tenon of face beam in its 3rd part was overlarge;(3)sinkage of the central caisson ceiling was obvious;(4)sinkage of tenon of its side beam was overlarge,but the beam had been strengthened by wooden supports.To protect Chinese ancient wooden buildings,these problems were studied by theoretical as well as simulation methods.Causes of the problems as well as strengthening methods were also discussed.Results show that:(1)main cause for overlarge deflection of the eave purlin is aging of wood material,which leads to decrease of elastic modulus,however the purlin is still safe enough;(2)overlarge sinkage of tenon of the face beam relate closely to overlarge tension,bending and shearing forces at the location,by steel-wood components the beam can be effectively strengthened;(3)main cause for sinkage of the caisson ceiling is crack of groveling beam above it,by iron band wrapping method the problem can be solved;(4)sinkage of tenon of the side beam relate closely to overlarge forces at the location,by additional supports the beam can be effectively strengthened.