Experimental Study On Mechanical Properties Of New And Old Wood Used In Timber Structure Building Under High Temperature

Wooden structure is the mainstream system of ancient architectural forms in my country,and its unique structural form and artistic attainments enjoy a high reputation in the world.Many magnificent wooden structures in ancient my country carry long historical and cultural information and are an important part of cultural heritage.However,because the wood used in the structure is inherently flammable,the wood structure building has defects in fire resistance and is extremely prone to fire.In the process of restoration of ancient wooden buildings after fire,the principle of “not destroying the value of cultural relics” in the restoration of cultural relics should be considered.In most cases,the wooden frames that are not affected by the fire will be kept,and the wood has experienced the high temperature in the fire Later,its mechanical properties will change.Therefore,on the basis of experimental research,it is very important to grasp the law of wood mechanical properties under high temperature.In this paper,based on the standard specimens of new and old wood of poplar and pine,the mechanical tests of compressive,tensile and shear properties are carried out,and the main mechanics of the new and old wood of poplar and pine in the two directions along the grain and the transverse grain are studied.The performance is affected by temperature and constant temperature time.At the same time,the differences and rules of the mechanical properties of different kinds of wood and old wood are compared and analyzed.Draw the following research conclusions:（1）High temperature effects（temperature gradient of 100℃,200℃ and 250℃,constant temperature time gradient of 15 min,30min,45min）have different degrees of mechanical properties such as compressive strength,tensile strength,shear strength and elastic modulus of wood Impact.With the increase of temperature and constant temperature time,the whole shows a different degree of decrease.（2）According to the experimental research data,the mechanical properties of wood subjected to high temperature are systematically studied through a variety of data processing methods such as variance analysis method and multiple regression analysis method,mainly focusing on the influence of temperature and constant temperature time on the mechanical properties of wood Discussion summary.The study found that the influence of temperature is more significant than that of constant temperature time.（3）When the type of wood is certain,after high temperature treatment under the same conditions,the mechanical properties of the new wood are mainly better than the old wood,especially the difference in tensile strength between the new and the old wood is obvious.（4）The wood is old and new to a certain degree.After undergoing the same high temperature treatment,a comparative analysis of poplar and pine wood found that the overall mechanical properties of poplar are better than pine,and there is a significant gap between pine and poplar in terms of cross-grain shear resistance.（5）On the basis of experimental research,the constitutive model of cross-grain compressive resistance of old poplar wood after high temperature,the compressive constitutive model of new pine wood along the grain and the tensile constitutive model of old pine wood along the grain were established.And refer to the model curve and the fitting effect of the test data to verify the reliability of the model.