Research On Hurricane Wave Force And Fragility Of Superstructure Of Coastal Bridge

With the large-scale construction of expressways and high-speed railways,as well as the extension of China's medium and long-term railway network from inland to islands,more and more bridges have appeared in the coastal areas of China.Different from bridges in inland areas,coastal bridges are vulnerable to complex marine dynamic environments such as typhoons,giant waves and even tsunamis,which leads to different degrees of structural damage and serious economic losses.It is of great significance for the safety of coastal bridges to accurately predict the wave force on the bridge girder and the damage probability of superstructures under the influence of storm surge and hurricane wave.At present,there are few researches on the wave force acting on box girder,a common cross-section form of offshore bridge in China,and there is a lack of corresponding analysis on the damage mode and damage probability of the whole bridge structure.Therefore,it is necessary to study the wave force on box girder superstructure and the structural vulnerability under hurricane waves.This paper studies the damage probability of the coastal box girder bridge under the action of hurricane waves.The main research contents are as follows:(1)The 1:30 scale wave hydrodynamic test of box girder model is carried out to study the wave force acting on box girder under regular waves with various submerged depth,wave heights and periods.The results show that the wave force on the superstructure includes quasi-static and slamming component.When the submergence coefficient is small,the slamming force component is large,which has a significant impact on the peak wave force.In addition,the current flow influence of the interaction of current and waves on the flow field and the force law of bridge structure are analyzed.And under different submergence coefficients,the variation law of wave current force with velocity is different.(2)A two-dimensional wave force calculation model of submerged box girder structure is established by using potential flow theory.The velocity potential of the whole river basin is solved by feature expansion matching method,and the wave force acting on submerged bridge slab is calculated by using Bernoulli principle.The correctness of the wave force calculation model is verified by compared with the experimental results.Based on this method,the effect of various dimension parameters of box girder structure on wave force is studied.The results show that the increase of the relative height of the upper flange and the relative width of the web will lead to the decrease of the vertical wave force and the increase of the horizontal wave force.The influence of various dimension parameters should be considered comprehensively in the structural safety design for hurricane wave action,(3)Random wave tests of box girder superstructure are carried out to study the influence of effective wave height,effective period and submerged depth on random wave force,and the characteristics of random wave force in frequency domain and time domain are analyzed.It is found that the distribution of wave force in frequency domain is similar to that of wave surface power spectrum,and it is transferred to high frequency and low frequency.Based on the potential flow theory method and the wave linear superposition method,the potential flow theory random wave algorithm of box girder structure is established.According to the experimental data,the correlation correction coefficients are analyzed by comparison,and the empirical calculation model of random wave force of submerged box girder structure based on the potential flow theory method is obtained.(4)Vulnerability analysis of coastal box bridge is carried out based on potential flow theory and structural dynamic analysis.The stochastic wave force history on the superstructure is obtained by the potential flow theory method,and the structural demand samples are obtained by the finite element dynamic time history analysis.The vulnerability curves corresponding to different damage indexes are obtained by using the assumption of normal distribution and regression analysis.The effect of different support types and connection modes on the structural vulnerability of coastal box bridges under the action of hurricane waves is studied.The vulnerability analysis shows that the bridge structure connected with ordinary rubber bearings is prone to damage under the action of random waves due to the lack of horizontal and vertical constraints,and the main form of damage is the horizontal slip between the beam and the bearings.The support and connection forms in the study have a certain effect on reducing the vulnerability probability of the box girder structure.The connection mode with vertical pullout resistance has a better effect on reducing the risk of hurricane waves.In particular,the bolt connection proposed in this paper is easy to install and design.It is suggested that the protective measures should be added in the future design of coastal bridges.