Study On Dynamic Response Of Submerged Floating Tunnel Structure Considering Traffic Load

The submerged floating tunnel(SFT)is an innovative traffic structure that crosses the deep waters after the sea-crossing bridge and the submarine immersed tunnel.It is an important alternative to solve major traffic engineering problems such as the fjord crossing and deep sea passage in the future.In recent years,it has been accepted by experts and scholars from all over the world.Meanwhile,a large number of related research were carried out.The dynamic response of SFT structures under various loads has always been the focus of this research field.In addition to focusing on the wave and current loads outside the SFT structure,the internal traffic loads are also worthy of further study.In order to study the dynamic response of SFT under traffic loads,this paper analyzes the composition and influencing factors of traffic loads in SFT,proposes appropriate traffic load simulation expressions,and reveals the dynamic response law of SFT under traffic loads through numerical simulation and model tests.The research work carried out mainly includes:(1)This paper analyzes the load classification of SFT at first.According to the formation mode and the action characteristics,the load types of the SFT can be mainly divided into environmental load,permanent load,functional load,deformation load and accidental load.Traffic load is the main functional load that the SFT is subjected to during the operational phase.(2)By comparing the characteristics of the traffic load of the SFT with the ordinary highway bridge and tunnel,the composition of the SFT traffic load is determined to include the fixed load and the additional dynamic load.The additional dynamic load consists of internal incentives and external excitation.The main factors of the SFT traffic load are:vehicle structure,road surface roughness,driving speed and external excitation load.(3)The vehicle load in highway traffic is selected as the research object of the SFT traffic load,using the moving vibration load to simulate the vertical force of the vehicle load.The simulation expression of the SFT traffic load under stochastic fluctuation conditions is proposed,after combining with the research results of the highway traffic load,and considering the influencing factors of the SFT traffic load.The simulation expression is closely related to the vehicle structure,road surface condition,driving speed and external excitation load,it can simulate the SFT traffic load in a certain extent.(4)Taking the dynamic load ratio as the evaluation index,the influence of the calculation parameters of the SFT traffic load on the calculated value of traffic load is analyzed.The analysis results show that the increase of the axle load of the vehicle makes the amplitude of the dynamic load ratio fluctuation curve decrease,the period is prolonged,and the dynamic load ratio is relatively reduced.As the driving speed increasing,the amplitude of the dynamic load ratio fluctuation curve is increased,the period is decreased,and the dynamic load ratio is relatively increased.The pavement roughness and the external excitation load affect the amplitude of the dynamic load ratio fluctuation curve,but the period is constant,and the amplitudes are proportionally changed.(5)The numerical analysis model of the SFT dynamic response is built by means of the numerical analysis software ANSYS.Based on the numerical model,the influence on the SFT dynamic response due to the simulation method,the loading method,the calculation parameters,the impact action,the limit conditions are analyzed.The numerical analysis results indicate that the moving vibration load in the traffic load simulation method is more suitable for simulating the SFT traffic load than the fixed uniform load and the moving concentrated load.The increase of the number of vehicles and the shortening of the vehicle spacing will promote the increment of the SFT dynamic response.The vehicle structure,road surface roughness and driving speed in traffic load calculation parameters have little influence on the SFT dynamic response,while the wave load in the external excitation load has obvious influence.The impact action of traffic load will be promote the increase of the SFT dynamic response,and the dynamic increments of different sections are inconsistent.The different loading modes under the traffic load limit conditions have different effects on the SFT dynamic response,but the relative displacement at the joint of the pipe section must be ensured within the control range.(6)In order to quantitatively analyze the influence of traffic load on the SFT dynamic response,the influence degree and influence weight of the traffic load on the SFT dynamic response are analyzed by orthogonal test and analytic hierarchy process respectively.The results reveal that the influence degree and influence weight of the wave current load are the largest,whether it is the vibration displacement or the upstream cable tension of the pipe section.(7)Through the large-scale SFT model test,the influence of traffic load on the dynamic response of the SFT structure and the influence of external wave load on the vertical load of the test vehicle are monitored.The test results show that the internal traffic load has a restraining effect on the cross-flow displacement and anchor cable tension of the pipe section model,and promotes the pressure around the pipe section.The external wave current load causes the test vehicle to act slightly on the vertical load on the upstream side and the back-flow side of the road panel.For the influence of vertical load,the wave in the external wave current load is more obvious than the water flow.(8)Comparing the numerical simulation results with the model test results,it is found that there are similarities and differences between the two results.The same point is:the wave current load has similar effects on the SFT dynamics response,it proves that the main design of model test is accord with numerical simulation;the different point is:the variation of the SFT dynamic response increment is inconsistent,which is due to the fact that the anchor cable materials of the two methods cannot be completely similar.