Numerical Study On Temperature Distribution And Mechanical Performance Of Inclined Steel Roof Under Typical Smoke Exhaust Conditions In Fire Disaster

The safety of long-span steel roof under fire disaster is important for fire resistance design of steel structure.Obvious discrepancy of temperature distribution under fire between flat and inclined roof indicates that strain and stress distribution on inclined roof cannot be correctly estimated by former design codes for flat roof.The influence of roof inclination on temperature distribution is investigated through the ceiling jet flow and FDS simulation,and the differences of mechanical properties of steel structure are analyzed when structure is under different temperature distribution.The main contents of this paper are:(1)The existing calculation formula of large space temperature field and design method of smoke extraction are introduced.Several simulation methods of slope ceiling are introduced and compared in FDS.(2)As for the condition that smoke extraction is not restricted,an approximate method is proposed to estimate the temperature variation with inclined angle ranging from 10° to 30° which based on the temperature computation model of unconfined ceiling jet.The stress and displacement are compared.The results show that the temperature of inclined roof decreases on the underside of projection and increases by 7% on the upside of projection,and the stress and displacement of inclined truss has not changed much under different temperature distribution,the difference is within 1.5%.(3)As for the condition that smoke extraction is restricted,an approximate calculation method is proposed to estimate the temperature variation with inclined angle ranging from 5° to 30° which based on FDS simulation.The stress and displacement of inclined truss are compared.The results show that the temperature of inclined roof increases in the local areas of the upside of projection and decreases in other areas.Temperature of inclined roof increases by 12% when the area of smoke extraction near the ridge satisfy requirements of the design code(2% of floor areas),and the stress and displacement of inclined truss has not changed much under different temperature distribution,the influence of roof angle on temperature distribution can be ignored.Temperature of inclined roof increases by 43% in the case of no smoke extraction near the ridge,the stress and displacement of inclined truss has changed much more,the stress and displacement difference are 50% and 20%,the influence of roof angle on temperature distribution should be considered.