Study On Structure Optimization Of Bottom Slab In PBA Station

With the development of social economy and the increase of traffic volume,traffic problems are becoming increasingly prominent.In order to alleviate the increasingly serious urban ground traffic condition,the construction of underground railway has become a trend.Therefore,the construction method and construction technology of the subway station have been constantly innovating.The PBA method has been widely used in the construction of Beijing metro station,and it has been developed from the previous eight-pilot-PBA method to the single-layer-PBA method which has less disturbance to the ground.The single layer PBA method is a construction method with pile,beam,column and arch as supporting system.At present,the theoretical analysis of this construction method is not comprehensive enough.Based on the Suzhou subway station of Beijing metro line 16,a numerical model of the single-layer-PBA method and an optimization construction method without bottom stringer are established.Through the comparison and analysis of the calculation results,we draw the following conclusions:(1)The disturbance in construction process occurs in excavation of the pilot and arch stage.The ground settlement and its regularities without bottom stringer remains the same as single-layer PBA method.(2)Before the bottom stringer is cancelled,the bottom plate presents a one-way plate trend,and there is a certain stress concentration around the column after bottom stringer is cancelled.The longitudinal plate belt at the side span still presents a clear trend of the unidirectional plate,and the plate element around the middle column presents a two-way slab trend of the beam free plate.The reinforcement moment of the station floor has not changed,but it has reduced the amount of reinforcement.(3)After analyzing the model of three dimensional load structure method,the optimized plate method calculation model of bottom plate,before and after floor structure optimization,is established.The bottom plate of single layer PBA method is all composed of type 1 units.The optimized floor structure is composed of type 1 unit and type 3 unit,and the load is transferred to two directions in vertical and horizontal directions.(4)The main role of the bottom stringer in the station is the shear and torsion,but the shear and torque are small,while the torque of the bottom stringer increases,but the value is still small,the shear value increases greatly,but still in the bearing range of the concrete floor.(5)In the optimized calculation results,the optimized lateral bending moment Mx can directly use the results of two-dimensional calculation,and the longitudinal bending moment My is within the range of reinforcement.Therefore,in the future station construction process,if the ground bearing capacity is enough and the groundwater level is within a certain range,the construction method of the bottom longitudinal beam can be considered.