| In recent years,with the rapid development of China’s construction industry,the forms of building structures have become increasingly diversified.Modern wood structures have once again become a hot spot in the construction field with their advantages of environmental protection,energy saving,and comfort.At the same time,Cross Laminated Timber(CLT)have emerged as a new type of wood structure material.According to statistics,the fire accidents in China’s buildings are on the increase year by year,and the use of wood as a combustible material requires special attention.The CLT structure is also inevitably facing the threat of fire.At present,only some foreign scholars have conducted relevant experiments and theoretical studies on the fire resistance of CLT structures.However,China’s research on the fire resistance of CLT structures is still at an exploratory stage,far from meeting the needs of CLT structural development and application.At present,there are NDS 2018(National Design Specification for Wood Construction 2018 Edition)and North America CLT manuals for foreign countries on the CLT fire protection design specifications.However,due to the lack of relevant research in China,there are no CLT-related regulations and standards.In summary,the research on the fire resistance of CLT structures has important scientific and engineering significance.In this paper,the domestic Cross Laminated Timber(CLT)slab is taken as the research object,and the charring rate test and the thermo-mechanical coupling analysis based on the finite element software ABAQUS using the cohesive elements are carried out.The main contents can be divided into the following parts:(1)From the viewpoints of wood charring mechanism,CLT charring rate and its calculation method,and CLT layer delamination mechanism were summarized and reviewed in terms of foreign scholars’ research achievements in the field of fire resistance of CLT structures and domestic scholars in the field of structural mechanical properties of CLT.(2)The material properties of the sawn timber used for the CLT floor were tested.In addition to the conventional timber property tests,the timber properties including adhesives were tested.(3)Using finite element software ABAQUS as a platform,a thermo-mechanical coupling analysis method for delamination of CLT floor based on cohesive elements was established.The “Model change” method was used to consider delamination to the temperature field.The delamination of CLT and the change of charring rate after delamination were analyzed to obtain the charring rate of the CLT accurately.The validity of the finite element calculation method was verified by an example.(4)Experiments on charring rate of CLT floors were carried out,the influence of fire time and delamination was observed.The results show that the CLT pressed by the PUR adhesive has the phenomenon of delamination,and the longer the time of fire,the higher the charring rate;for the CLT with the phenomenon of delamination,the charring rate depends on quantity and thickness of lamination,with the same total thickness,the fire resistance of the 3-layer CLT is better than the 5-layer CLT;which the original wide vertical seam of CLT is one of the reasons that affect its fire resistance.(5)Simulation of CLT floor exposed to fire was conducted and the differences between experiment and simulation were compared.Based on this,the effects of fire time and tree species on the charring rate of CLT with delamination were analyzed.The results show that the finite element calculation results after considering the delamination are in good agreement with the tests.For CLT with delamination,the fire resistance is reduced with smaller strength.(6)Combined foreign timber structure design code,the criteria for determining the delamination of CLT based on the charring rate test are proposed,the model of charring depth considering delamination is improved,which provides reference for engineering designers to carry out CLT structural fire protection design. |
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