Force Characteristic Analysis And Criteria Of The Key Components Of Prestressed Steel Truss Under High Temperature (Fire)

Nowadays,the utilization of steel structure are based on the fire prevention design.However,there is a lack of the usage of mechanical characteristics in fire.Although relevant stardards and specifications has been compiled,there should be more research findings to support the result,and the findings can not guarantee the sufficient fire resisting.The prestressed steel trusses also face the same problem.Due to the insufficient fire resisting,the broken critical element caused by coupled thermo-mechanical have a negative influence on the stability of a trussed construction.Therefore,the research on a prestressed steel truss and key components in the effect of coupled thermo-mechanical is a popular topic in structural safety evaluation.This dissertation performed the following work based on the problems pointed out above:(1)Summing up and analyzing existing researches,both in China and abroad.The appropriate temperature curve is selected and it makes the simulation analysis of temperature field is more close to the actual situation.(2)The whole structure are systematically analyzed by a finite element analysis software for the overall thermodynamic coupling structure,and the research also uses the analysis of materials nonlinearity and geometric nonlinearity.Then the characteristic stress-strain curves of the structure,which changes over time,could be concluded based on the analysis.(3)The average stress ratio,the reliability and energy methods are applied to determine the key components of prestressed steel truss under the high temperature(fire).Then evaluating the advantages and disadvantages of the three methods.According to the research,the main results could be drawn as follows:(1)The key components of prestressed steel truss are the joints of lower chords in supported section and upper chords in mid-span section,which bear the maximal average stress,are minimum reliability and would have the greatest influence on the surrounding components if they are damaged.Hence,focused fire protection should be carried out here.(2)The critical coefficient of upper and lower chords in the prestressed steel trussare generally higher than web members.Consequently,the general fire protection should be applied on the the upper and bottom chords except the key components.(3)The web members of prestressed steel truss have little effect on performance of fire resistance.Therefore,the fire protection could be reduced appropriately.(4)The prestress loss of the prestressed cable stress is relatively small in large space fires.(5)According to the analysis and co MParison of three ways,the method of average stress ratio is suggested to be implemented in real project.The analysis and determination methods for force bearing features of the key components of prestressed steel truss under high temperature(on fire),which could provide a reference for the design and analysis of the prestressed steel truss in the future.