The Components Design For Addition Basement In Existing Building

With the acceleration of urbanization,efficient and reasonable utilization of underground space resources is the requirement of the era.Not only could it cope with the issues concerning parking problems as well as traffic jam in an effective way,but could also serve as a civil air defense project to improve civil air defense preparedness and disaster prevention and mitigation capabilities,therefore,the study of the underground addition of existing buildings is of great significance.Replacement piles and support beams are the key components of the underground layer of existing buildings.With the excavation of the basement,the exposed length of the pile body rises while the stability of the pile decreases.As a conversion member that connects the top and bottom,the support beam plays an important role in the success or failure of the support project.Ansys finite element analysis software was applied in this paper,to make an analyses of the bearing capacity of pile replacement and support beam in the basement of an existing building,and proposed a calculation formula and component design.Lastly,by monitoring the actual engineering,we testified the reliability of the design method,increaseing the safety reserve of the structure.(1)In accordance with the pile arrangement way of supporting pile in the middle of the upper vertical members,finite element analysis has been carried out on reinforced concrete precast square piles by changing the ratio of reinforcement,eccentricity of vertical load as well as the setting lateral support in the middle of pile body.The ultimate bearing capacity as well as stability coefficient of pile accelerates with the enhancement of reinforcement ratio.The bearing capacity is significantly improved after the lateral support is set in the middle of the pile body.Therefore,after the earthwork excavation reaches the corresponding design level of the beam plate,the beam plate should be constructed as soon as possible as the lateral support of the pile body to assure the the pile replacement of its stability.(2)In terms of the pile arrangement approach of supporting piles around the vertical components,we formed a three-dimensional finite element analysis model concerning steel pipe piles and the excavation depth,support addition position,support stiffness and number of supports around the pile were changed in turn,and the change law of bearing capacity of buckling stability of micro steel pipe piles has been researched,with the results demonstrating that,the ultimate bearing capacity of buckling stability gradually decreases with the rise of excavation depth.After the lateral supports are set,the extramural stability capacity of the pile increases with the increasing number of supports and stiffness.When the support is placed in the middle of the excavation depth around the pile,the buckling limit load is maximized.In terms of the results of numerical analysis,the stability calculation formula of pile foundation based on virtual fixed point method is proposed.(3)The three-dimensional finite element analysis model concerning steel pipe piles was established in terms of the pile arrangement approach of supporting piles around the vertical components and changing the excavation depth,support addition position,support stiffness and number of supports around the pile in turn,the change law of bearing capacity of buckling stability of micro steel pipe piles has been researched,with the results demonstrating that the ultimate bearing capacity of buckling stability gradually decreases with the rise of excavation depth.After the lateral supports are set,the extramural stability capacity of the pile increases with the increasing number of supports and stiffness.When the support is placed in the middle of the excavation depth around the pile,the buckling limit load is maximized.In terms of the results of numerical analysis,the stability calculation formula of pile foundation based on virtual fixed point method is proposed.(4)Component design was carried out for the seven-story concrete frame structure to add two basement floors downwards.In the construction phase,the wind load value is also reduced without considering the seismic load.In the normal use stage,seismic loads and wind loads need to be considered,and the values cannot be reduced.Based on the bending moment,shear force as well as axial force envelope diagram,the reinforcement of the vertical members and support beams in the basement and the structural measures of beam and column joints are obtained.(5)Stress monitoring of pile replacement was carried out for an underground layer enhancement project in the commercial port area of Jinan City.From the monitoring results,it can be seen that the maximum stress of the steel pipe on site is 32.2N/mm~2,which is less than the calculated stress of 46.4 N/mm~2,and less than the design value of steel strength of 215N/mm~2.This shows that the finite element numerical analysis results are safe and reliable.