Experimental Study On Fire Performance Of Typical Components Of Traditional Timber Structure

Plaster protection is a common surface modifying technique in Chinese traditional timber buildings,which prevents timber structural components from decaying and worm.However,it is unclear how plaster layer affects the performance of wood structural members under fire.To learn the fire resistance and residual bearing capacity of typical components of traditional timber structure,fire tests were carried out on timber beams and columns which were protected by craftwork with one hemp fiber and five plastering application.In addition,the numerical simulation method was adopted to provide contrast.The main conclusions are listed as follows:(1)The relationship between the fire resistance and loading ratio,sectional dimension and surface treatment was studied.It was found that the fire resistance increased with the increase in the sectional dimension and reduced with the increased in the loading ratio.After the craftwork with one hemp fiber and five plastering application was applied on the surface,the fire resistance improved apparently and the larger the loading ratio,the stronger this improvement.(2)The char layer formed on the surface of wood under fire.The residual cross section of wood column was circular when the initial cross section was circular.However,the residual cross section of wood beam was in the shape of ‘U’ when the initial shape was rectangular due to the effect of increased charring at corners.The charring rate of the bottom side was higher than those of lateral sides.After the craftwork with one hemp fiber and five plastering application was applied on the surface,the charring rate decreased obviously.(3)The approximate formula was programmed for the fire resistence of timber columns based on strength reduction method.The calculated results were in good agreement with the experimental ones.(4)The VUMAT subroutine was encoded for wood which was an anisotropic material and performed differently under tensile and compressive stress.The stressstrain relation,model of thermal properties,failure criteria and damage evolution model were defined.(5)The VUMAT subroutine was incorporated within ABAQUS finite element software for thermo-mechanical coupled analysis.The results of the numerical simulation method agreed well with the experimental data.(6)The residual bearing capacity of timber beams and columns were studied.It was found that the residual bearing capacity and initial stiffness decreased apparently after exposure to fire and the descent degree decreased after the craftwork with one hemp fiber and five plastering application was applied on the surface.(7)The power function relationship between the charring rates and the exposure time was found and a approximate formula was presented.(8)Based on the strength reduction method,a theory formula was obtained to calculate the residual bearing capacity of short columns.Values of reduction coefficient were calculated for timber columns with/without the craftwork with one hemp fiber and five plastering application.