Study On Fire Performance Of Cross-Laminated Timber Panels Based On Reduced-Scale Model

With the continuous development of low-carbon building and urbanization in China,middle and high-rise wooden structure will have a broad development prospect.Cross-laminated timber（CLT）is a new type of wood structure product.Due to the concern of CLT’s own flammability,the wide application of CLT in middle and high-rise wood structure is largely limited.Further study on its fire performance is needed.At present,the most direct way to study the fire performance of wood structure is to conduct the fire test of full scale structure,but the full scale experiment tend to have set the difficulty big,test process is difficult to handle,poor repeatability,using similarity theory as a tool,based on the structure of the prototype design of scale model fire test is helpful to solve the difficulties of full scale test.In this paper,the similarity theory of thermal-mechanical response of CLT floor was studied.In this paper,thermal-mechanical response similarity theory of CLT floor is derived firstly.Then,the flexural performance tests and temperature field similarity theory verification tests of CLT floor slabs with different scale ratios（1:1,2:3,1:2）are carried out successively.Based on the tests results,finite element simulation and similarity analysis of fire resistance limit are carried out.The research content is mainly divided into the following parts:（1）The research status of wood size effect,fire resistance of wood structure and fire resistance test of scale model are introduced.In terms of wood size effect,there is no study on the size effect of CLT floor bending strength in the existing public literature.In the aspect of fire resistance of wood structure,there are many researches on the fire performance of wood structure under standard fire,and the researches on the fire performance of wood structure under non-standard fire are gradually carried out.At the same time,the calculation method and simulation method of fire resistance limit of wood structure under non-standard fire are lacking.In terms of scale model fire resistance test,the main test methods originated from abroad.In recent years,some domestic scholars have carried out the fire resistance test of concrete structure and steel structure,but there is no public literature to carry out relevant research on wood structure.（2）The similarity theory and scale model test are introduced,and the similarity theory of thermo-mechanical response of CLT floor fire resistance limit test is derived.In the derivation of similar loading conditions,the size effect on the improvement of the flexural strength of the reduced scale specimen is considered.The ratio"S_F,b"between the flexural strength of the reduced scale model and the prototype is used to modify the load holding value of the reduced scale model,and the relative stress coefficient"K"is introduced to compare the similarity of the stress distribution of the midspan section between the prototype and the reduced scale model;In the derivation of the similar conditions of temperature field,due to the lack of mathematical model that can accurately simulate the mechanism of wood pyrolysis and the lack of temperature field simulation means under the temperature rise curve other than standard fire,this paper ignores the influence of the increase of heating rate on the thermal parameters of scale model specimens and wood pyrolysis（3）In order to study the size effect of flexural strength of CLT floors with different scale,and obtain the ratio"S_F,b"between the flexural strength of scale model and prototype,three groups of flexural performance tests of 9 CLT floors were carried out.There are three specimens in each group,"A11 group"specimens are prototype specimens,and"A23 group"and"A12 group"specimens are scale model specimens.The effects of scale ratio on the flexural ultimate bearing capacity,flexural elastic modulus,flexural strength,failure mode,load displacement curve and other flexural properties of CLT floor slab are studied.（4）In order to verify the applicability of temperature field similarity theory to CLT floors when ignoring the influence of heating rate increase on thermal parameters of scale model and wood pyrolysis,three groups of temperature field similarity verification tests of three CLT floors were carried out.Based on the temperature field similarity conditions in the second chapter of this paper,the temperature rise curve of the scale model is deduced,and the similarities of the delamination time,temperature field distribution,carbonization depth,carbonization rate,carbonization depth and smoldering rate in the temperature rising section of the prototype and the scale model are compared.（5）Based on the above test results,the fire resistance limit of CLT floors with different load holding levels（20%and 30%）were simulated with ABAQUS finite element simulation software under the two conditions of considering and not considering the delamination.Due to the lack of effective simulation means of wood temperature field under non-standard fire,and the similar conditions of carbonization depth in wood smoldering stage need to be further studied.In the finite element simulation of fire resistance limit of CLT floor,the prototype specimen adopts standard temperature rise curve.The similarity analysis of the simulation results of temperature field distribution,mid span section stress distribution,carbonization depth,carbonization rate,mid span displacement and fire resistance limit between the prototype and scale model are carried out to verify the correctness of the thermal stress response similarity theory of CLT floor fire resistance test in Chapter 2 of this paper.