| China’s urban rail transport mileage has reached 4152.8 km by the end of 2016,where the subway accounted for 76.3%.The rail transit line under construction is 5636.5 km,and the planning transit line is 7305.3 km.The number of subway stations increased to 2671 with the construction of the subway,and there were 437 transfer stations which accounted for 17.1% of the total subway stations.China locates in the two largest earthquake belts in the world,thus the earthquakes occurred frequently.A large number of personnel and economic losses has been brought by earthquakes.In June 2016,China has abolished the act of non-seismic fortification zones in the new China earthquake motion parameter zoning map,and increased the seismic fortification of the engineering structures under the action of the extra-large earthquake.With the increasing number of large and complex underground structures in China,the seismic problems are extremely striking.Taken the Daikai subway station as an example,the ultimate seismic capacity of underground structures is studied from two perspectives: the deformation and bearing capacity of structure itself and the seismic action.The main innovations include:(1)The failure mechanism of shallow underground structure frame structure is firstly concerned.The horizontal deformation capacity and vertical bearing capacity are analyzed.Then the ultimate deformation state and ultimate state are determined based on the characteristics of Daikai subway station in the failure process.Furthermore,the damage ratio of the horizontal and vertical direction of the structure is defined based on the limit state.It is used as the evaluation index to reflect the seismic performance of the structure.The horizontal failure ratio is related to the axial compression ratio,which reflects the influence of axial compression ratio on the structural deformation capacity.The magnitude of the failure ratio reflects the deformation capacity and the bearing capacity of the structure.It is concluded that the structure is destroyed when the failure ratio is greater than 1,while it is not damaged when the failure ratio is less than 1.(2)For the shallow underground structure framework,the method to analyze the seismic capacity of the structure limit of two aspects from the state structure itself and external conditions is proposed: the structure of the ultimate deformation capacity of the envelope,the vertical ultimate bearing capacity value judgment standard as structure limit state.The evaluation index which reflects the degree of structural response is defined by the criterion of judgment,which is the ratio of horizontal to vertical failure.Calculation of structural response under different loading conditions,obtained in each seismic conditions under earthquake loading structure limit,the limit value of the comprehensive seismic response state in the partition structure of horizontal and vertical ground motion under the condition of PGA,I,II and III three interval.The local vibration PGA conditions in the I range,the structure is not damaged;the local vibration PGA conditions in the III range,structural damage;local vibration PGA conditions in the II range,the destruction of the structure and characteristics of earthquake related.The II range is the ultimate aseismic capacity of the structure.(3)The earthquake response,seismic weak components and possible failure reason of the double frame structure of Daikai subway station are analyzed in this paper.The failure mechanism of the shallow buried frame structure and the rationality of the analysis method of ultimate seismic capacity are verified.Finally,several suggestions are put forward to guide the earthquake-resistant design of structure: in the horizontal direction,the deformation capacity of structural column is higher than that of the side wall,the side wall has sufficient stiffness to resist lateral deformation;in the vertical direction,the vertical bearing structure must has enough capacity to bear the effect of overlying soil. |
PDF Full Text Request