Study On Fire Resistance Of Jointed Wooden Beams In Village And Town Buildings

Wood is one of the natural materials given to people by nature.As a kind of green building material,it is widely used in practical engineering.In the traditional timber structure of our country,when the size of the timber can not meet the requirements,the method of combining small pieces with large pieces is often adopted to solve the stress problem of the long-span members.However,in the traditional jointed method,only two wooden beams are placed on top of each other without any connection between the contact surfaces,so the two wooden beams cannot realize the cooperative force.Moreover,due to the large gap of the contact surfaces,the fire area of the wooden beams are increased,so that the fire resistance of the nonjointed wooden beams are low.Therefore,this paper proposes the method of jointed wooden beams for improvement.The jointed wooden beam is made of the upper and lower wood beams closely jointed by screws.Jointed wooden beam can obviously improve the bearing capacity and stiffness of component,reduce the fire area of the component,thereby improving the fire resistance of the components and reducing the casualties and economic losses caused by the fire.Therefore,this article is of great significance to the research on the fire resistance of wood structure buildings.In this paper,jointed wooden beam and non-jointed wooden beam are taken as the research objects.Based on the finite element software ABAQUS,the bending performance and fire resistance of each group of specimens are studied.The main contents can be divided into three parts:(1)As the time exposed to fire increases,the closer to the fire surface,the faster the temperature rises.The variation trend of measured temperature on the fire surface is close to the standard and natural heating curves.The temperature distribution of the wood cross section is divided into two regions with the center line of the vertical screw as the dividing line.(2)The slippage of jointed wooden beam on the contact surface is significantly smaller than that of non-jointed wooden beam at room temperature;The deformation range of the end screw is obviously larger than that of the mid-span region.The ultimate load of jointed wooden beam is at least 43% higher than that of non-jointed wooden beam.The ultimate load of jointed beams increases with the increase of screw diameter and screw length.The ultimate load obtained by the screw partial oblique insertion(45°)is greater than that obtained by the whole vertical insertion(90°).(3)When the load holding levels are all 20%,the fire resistance of D8,D10 and D12 are3 times,3.3 times and 3.6 times higher than that of non-jointed wooden beam,respectively,that is,the fire resistance of jointed wooden beam is significantly higher than that of non-jointed wooden beam.The fire resistance of jointed wooden beam increases with the increase of screw diameter and screw length.Reducing the load holding level can greatly increase the fire resistance limit of jointed wooden beam.The fire resistance time obtained by partial oblique insertion(45°)of the screw is greater than that obtained by full straight insertion(90°).The fire resistance limit of jointed wooden beams under standard heating condition is slightly higher than that under natural heating condition.