Structural Response And Residual Capacity Prediction In Multi-chamber(Cabin) Fire

Steel structure is widely used in multi-chamber(cabin)structure fields such as ships,fast-installed buildings,logistics and warehousing due to its advantages of light weight and fast construction.However,the high temperature caused by fire will degrade the mechanical properties of steel,resulting in structural thermoplastic deformation and loss of bearing capacity.The spatial characteristics,fire source types and material characteristics of multi-chamber(cabin)structure are different from those of other building structures,which makes the fire spread and temperature transfer more quickly,leading to more serious local deformation and even collapse.Therefore,it is necessary to study the spatial temperature field and structural response of multi-chamber(cabin)structure in different fire scenarios.The change of residual bearing capacity of multi-chamber(cabin)structure in fire is further explored to provide reference for the safety assessment of multi-chamber(cabin)structure in fire.Based on the large eddy simulation algorithm of fire dynamics and the structural thermal-mechanical coupling response method,this thesis realized the fire-thermal-structural coupling calculation of multi-chamber(cabin)structure in real fire.Taking the typical ’I-shaped’ cabin as an example,the fire spread characteristics and time-varying law of spatial temperature field of multi-chamber(cabin)structure under fire were studied.On this basis,the three-dimensional spatial temperature field was used as the thermal boundary condition of the structure to obtain the structural temperature distribution,and then the time-varying distribution law of the temperature field and stress field of the multi-chamber(cabin)structure under real fire was studied.The failure characteristics and failure modes of multi-cell structure in different fire power and different fire positions were further studied,and the prediction model of residual bearing capacity of multi-chamber(cabin)structure after fire was proposed.The main following work were carried out:The effects of different fire power and fire location on fire spread characteristics and spatial temperature field distribution of multi-chamber(cabin)structure were studied.The results show that the spatial temperature transfer of the fire source layer is obvious,and the fluid state at the door can be divided into the lower air entrainment zone(below 1m),the central stable zone(1m–1.4m)and the upper flue gas overflow zone(above 1.4m).The smoke in the corridor produces backflow phenomenon.The smoke in the side chamber forms a backflow at the corridor,while the smoke in the middle chamber forms two backflows at the corridor.The boundary between the upper and lower layers of the backflow layer is roughly 1.6m.Compare with 2500 k W,the height of smoke layer at 5000 k W downstairs decreased by 26.7%.The chimney effect at the stairs caused by the side chamber fire accelerates the temperature transfer process in the upper space.The time-varying distribution of temperature field and stress field of multi-chamber structure under fire was studied.The results show that the high temperature region of the structure is mainly concentrated in the door of the ignition cabin and the nearby web beam.Due to the small specific heat of steel,the structural temperature under fire increases by 21.6% compared with the ambient temperature.The intervention of temperature load and the constraint between components lead to the stress redistribution of the whole cabin and the stress level increases.When the fire power is 4000 k W,the stress of the deck under thermal coupling increases by nearly 66.7% compared with that under working load,and local buckling occurs.Due to the reduction of material properties at high temperature,the yield strength of the material at the longitudinal bone of the deck decreased by 42%.The failure mode and residual bearing capacity of multi-chamber(cabin)structure under different fire power and fire location were studied.The results show that when the fire power is below 3000 k W,the damage location of the cabin gradually expands from the sagging plane to the two ends.In 4000 k W,the failure path gradually expanded from the fire source side to the sagging plane;the proportion of failure parts near the fire source side in the failure path is greater than that in the sagging plane at8000 KW.In addition,the residual carrying capacity of cabin in fire is related to the fire power.In this thesis,the mathematical models of the ultimate strength reduction coefficient of catin in different fire positions(side chamber and middle chamber)with the change of fire power are established,which can predict the residual carrying capacity of catin in fire from 2500 k W to 8000 k W,and realize the simplification of the model.The research results of this thesis have a reference value for fire safety assessment and fire resistance structure design of multi-chamber(cabin)structure.