Experimental Study On The Residual Bearing Capacity Of Cross-laminated Timber Wall-to-floor Joints With Steel Angle Bracket Connections After Fire Exposure

With the acceleration of the urbanization process in China,various buildings and structures have sprung up like mushrooms,but there are many problems that need to be solved,such as huge energy consumption and serious pollution.Wood,as a renewable main building material,is far more environmentally friendly than concrete and steel in terms of energy consumption,greenhouse gas,air and water pollution,and the exploitation of ecological resources.It is recognized as a green and environmentally friendly building material.Cross Laminated Timber is a kind of building material made of solid wood sawn timber or structural composite board orthogonal assembly billet,which is usually used in multi-story timber structure.The fire disaster brings much more harm to high-rise buildings than low-rise buildings,and the flammability of wood further exacerbates this effect.In order to accelerate the development of multiple high-rise timber structures in China,it is of great significance to conduct fire resistance research on CLT structures.Many scholars at home and abroad have carried out fire resistance research on CLT structures,but few related papers have been published on CLT joint connection.Therefore,taking the platform-type CLT wallto-floor joints with steel angle bracket connections as the research object,monotonic tests at ambient environment,standard fire tests,residual bearing capacity tests after fire exposure,ABAQUS finite element simulation of above tests,the calculation method of residual bearing capacity were carried out.The main research contents are as follows:(1)The monotonic tests at ambient environment were carried out on the CLT wall-to-floor joints with steel angle bracket connections,and the basic mechanical performance parameters such as peak load,yield load,joint stiffness and ductility under different self-tapping screw lengths were obtained.The results show that increasing the length of the self-tapping screws can increase its initial stiffness and shear strength,but the ductility will be reduced.(2)The standard fire tests were carried out on the CLT wall-to-floor joints with steel angle bracket connections,and the charring rate,charring depth and temperature field distribution were obtained.The results show that the heat gained from the front face is greater than the side face,the depth of charring is greater,and the charring rate is faster;the protective measures of fireproof gypsum board and refractory cotton can greatly delay the time of CLT charring.(3)The residual bearing capacity tests after fire exposure were carried out on the CLT wall-to-floor joints with steel angle bracket connections,and the basic mechanical performance parameters such as peak load,yield load,joint stiffness and ductility after fire were obtained.The results show that after 20 minutes of fire,the initial stiffness and yield load of the CLT wall-to-floor joints are very serious.The decrease of the peak load is less than the yield load,and the ductility is improved.the use of fire-resistant gypsum board and refractory cotton can effectively improve peak load of CLT wall-to-floor joints after fire.(4)ABAQUS was used to simulate the monotonic tests at ambient environment,standard fire test and residual bearing capacity test after fire of CLT wall-to-floor joints with steel angle bracket connections,respectively,and compared with the test results,the simulation results were in good agreement with the test results.(5)Based on the calculation method of the bearing capacity of the CLT wall-to-floor joints with steel angle bracket connections at ambient environment,the calculation method of the remaining bearing capacity after fire was given.Compared with the experimental value,the calculation result was conservative,which can provide a certain reference value for engineering designers.