Study On Structural Response Analysis And Safety Assessment Method Of Bridges In Bohai Sea Under Dynamic Ice Loads

The Bohai Sea is the sea area with the most serious ice situation in China.As a special load of bridge structure in Bohai Sea,dynamic ice load may cause strong vibration,affects the normal operation of the structure,and even could cause fatigue damage of the structure.However,at present,there is a lack of evaluation methods for fatigue damage and driving safety of bridge structure under dynamic ice load,which makes the bridge anti-ice design lack of basis.Therefore,this paper aims at the problem of ice induced bridge structure vibration in Bohai Sea.Based on the study of two dynamic ice load modes,which are random ice force and self-induced ice force.The analysis model of bridge structure response under random vibration and steady vibration caused by ice is established.The fatigue damage assessment method of bridge structure under the action of random ice force and the driving safety assessment method under the action of self-induced ice force have been pushed forward,which provides a foundation for the anti-ice design of bridge in Bohai Sea.The main research contents and conclusions are as follows:(1)Based on the regression analysis of the ice force data measured in the field,the effective ice pressure calculation formula considering the ice velocity effect is given,which effectively improves the calculation accuracy of the local extreme ice force on the structure.For vertical ocean circular ice structure,considering the influence of incident angle and tangential ice force,the total ice force spectrum matrix is constructed.The calculation method of the total ice force of the structure synthesized by the local extreme ice force is given,and the simulation of the random ice force process of the vertical ocean wide structure is realized.By comparing with the ice force data of the lighthouse structure,it is found that the simulated extreme ice force of the lighthouse structure is close to the field measured result,which verifies the correctness of the method.Using this method,the random ice force process of the structure can be simulated in a large scale,and the statistical characteristics of the extreme ice force required for the anti-ice design of the structure can be provided.(2)By considering the elastic deformation,fracture length and the nonlinear relationship between ice strength and stress rate,a simulation method of self-induced vibration of ice induced structure based on negative damping effect is established.By using this method,the steady-state vibration response and self-induced ice force of ice induced structure can be simulated,and the frequency locking phenomenon in the process of ice structure interaction can be reproduced.Through the comparison and analysis with the scale model test and the field measured ice vibration data,it is found that the simulated ice force and structure vibration are basically consistent with the measured results,which shows that the method has high simulation accuracy.(3)Based on the typical geological,hydrological and ice force conditions in Bohai Sea,considering the joint influence of the hydrodynamic force and the non-linear of the soft foundation,the bridge structural response analysis models under the action of random ice force and self-induced ice force are established respectively.Taking the typical feasible scheme of bridge in Bohai Sea as an example,the random vibration and steady vibration of bridge structure caused by ice are studied respectively,and the dynamic response law of bridge structure under different foundation and water depth conditions is obtained.The results show that the dynamic response of bridge structure is greatly magnified by the soft foundation and deep water condition.When the structure vibrates in steady state,the main frequency of self-induced ice force is controlled by the vibration frequency of the bridge structure.The dynamic response of the bridge structure largely depends on the speed of ice,which reveals the coupling mechanism of ice and bridge structure when the bridge vibrates in steady state.(4)Random vibration caused by ice has high frequency and long duration,which should be considered in fatigue damage analysis of ice induced structures.Therefore,using the statistical model of ice parameters in Bohai Sea,the joint probability distribution of ice parameters in Bohai Sea is given,and the fatigue damage assessment method of ice induced bridge structure considering the combination probability of ice parameters is proposed.Based on the rain flow cycle counting method and Palmgren-Miner method,the cumulative fatigue damage of ice induced bridges under different water depth and foundation conditions is analyzed.The results show that both the soft foundation and the deep water condition will increase the cumulative fatigue damage of the bridge structure,that is to say,reduce the fatigue life of the structure.Based on the stress analysis of the steel pipe pile section of bridge,the cumulative fatigue damage distribution law of the stress points of the section is obtained,which provides a reference for the fatigue design of bridge caused by ice.(5)The occurrence probability of ice induced steady state vibration is low,but the amplitude is large,which may seriously affect the driving safety on the bridge.In this paper,the contact relationship between wheel and bridge deck is defined by penalty function method,and vehicle bridge coupling is realized by the contact force between vehicle and bridge.Then,the dynamic analysis framework of the vehicle,bridge and ice interaction system,the system is established by using the self-induced vibration simulation method of the ice induced structure proposed in this paper,and the evaluation method of the driving safety and comfort of the bridge under the steady state vibration of the ice-induced bridge is proposed.The results show that the interaction between the vehicle and the bridge is affected by the ice force and the vehicle speed.With the increase of the ice force and the vehicle speed,the vehicle’s side slip resistance is significantly reduced.Under the most unfavorable conditions proposed in this paper,the vehicle does not slip,but is close to the side slip state.In the case of no ice,the driver’s driving comfort is not affected,but with the increase of ice force and speed,the driving comfort decreases.Through the calculation of the bridge type in this paper,it is found that there is a problem of driving comfort,which is extended to other bridges.If the vehicle,structure,ice force and other calculation parameters will change,it may affect the evaluation results of driving comfort.