Study On Temperature Effects Of Complex Steel Structure During Construction Stage And Service Stage

Due to environmental temperature and welding,there will be deformation and complex residual stress during the construction of steel structure,which may affect construction safety.The environmental temperature during the service stage will change the internal force and the structural modal parameters of steel structure,thus affecting the accuracy of damage warning.The influence of temperature on the static performance and dynamic characteristics of complex steel structures is more complicated,therefore,it is an urgent demand to research the temperature effect in the course of its construction and service.In this paper,the environmental temperature effect in construction stage,welding residual stress and environmental temperature effect in service stage of complex steel structure are studied by via field test combined with numerical simulation.The main contents and achievements are as follows:(1)A model simulating the construction temperature field of complex steel structure was established.The effective temperature of components under solar radiation was corrected based on the principle of stress equivalence,and the monitored effective temperature of components is nonlinear fitted by two normal distribution functions.So the model simulating the temperature and construction field of complex steel structure was established,which was applied to simulate the steel construction of Whitewave River Ferris Wheel.The results showed that the daily temperature difference of the effective temperature of the components was consistent with Boltmann distribution;the limit temperature should be adjusted according to the effective temperature of components when temperature effects analyzed;the simulation results based on the temperature field model were relatively well matched with the measured results.(2)The environmental temperature effect during the construction of complex steel structure was analyzed.The influence of installation temperature of components and installation process on static performance of complex steel structure was analyzed based on the construction temperature field model,as well as the influence of the healing temperature of construction on maximum stress of the structure.The results showed that both the installation temperature and the installation process of the components would affect node displacement and rod piece stress after completion.The maximum stress difference of Whitewave River Ferris Wheel was 48 MPa and 72 MPa respectively.To determine the healing temperature of construction by considering the mechanical response on different parts of the structure could reduce the maximum structure stress of Whitewave River Ferris Wheel by 40 MPa.(3)The influence caused by the residual stress of wide butt welds on complex steel structures was analyzed.The weld width was difficult to control during the process of steel structure construction.The residual stress distribution pattern of the wide butt weld in complex steel structure was tested by blind hole method and numerical simulated by SYSWELD,based on which the impact of wide butt weld residual stress on static performance of complex steel structures was analyzed,as well as the effectiveness of stress relief treatment via the ultrasonic impact method.The results showed that the peak value of welding residual stress increased with the weld width,and the maximum value was close to the yield strength of base metal.The influence of weld shrinkage deformation on the internal force of rod pieces at the joint of Whitewave River Ferris Wheel should not be neglected.The ultrasonic impact method could effectively eliminate the residual stress of wide butt weld.In the test,the peak values of transverse and longitudinal residual stress of the four welds were reduced by 22% and 28% respectively.(4)The effects of environmental temperature on static performance and modal frequency of complex steel structure were studied.The influence mechanism of environmental temperature on structural static performance and modal frequency was discussed.Comparison of numerical simulation results and measured data of Whitewave River Ferris Wheel revealed the temperature influence law of the static performance and the modal frequency of the complex steel structure.The effect of BP neural network technology to eliminate the influence of environmental temperature was studied.The results showed that the environmental temperature changed the modal frequency mainly by changing the elastic modulus of materials and the internal force and geometric state of structure.The displacement of the upper structure of Whitewave River Ferris Wheel was sensitive to temperature changes,while the stress of the lower structure was sensitive to temperature changes.The modal frequency decreased while the temperature increased,and the maximum amplitude of variation of the first 4 frequencies during the monitoring period was 3.04%.BP neural network could reflect correctly the relation between modal frequency and environment temperature.The influence of environment temperature on modal frequency of the structure could be effectively eliminated by the established frequency-temperature regression model.(5)An early warning method of damage for complex steel structure taking account of environmental temperature influence was established.The particle swarm optimization(PSO)algorithm was used to optimize the parameters of the support vector regression-time series(SVR-ARMA)combination model.The damage warning method of complex steel structure was established by mean control chart and the PSO-SVR-ARMA model.The effectiveness of the proposed method was verified by hypothesis testing method simulating different degrees of damages.The results showed that PSO algorithm could improve the generalization ability and prediction accuracy of SVR-ARMA combination model.Compared with the basic SVR model,the frequency prediction accuracy of the established PSO-SVR-ARMA model was improved by 22%.The damage warning method based on PSO-SVR-ARMA frequency prediction model could identify the abnormal changes in the frequency caused by slight structural damage and had good damage warning precision.