Analysis And Research On The Design Of A Frame Core Tube Structure With A Large Opening In The Floor Slab

With the expansion of buildings,land resources have become scarce,so high-rise buildings are not uncommon in large cities,which not only satisfy the efficient use of land resources,but also become a symbol of the city.The typical frame-core tube structure is one of the most common high-rise building structural systems,and its significant practical advantages determine its wide application.In order to meet the requirements of the building,many high-rise buildings have opened holes in their bottom floors to obtain greater clearance,which is very likely to cause the structure to become an over-limit high-rise structure that does not meet the requirements of the specification.This paper takes the actual project of a frame-core tube structure with a large opening in the bottom equipment mezzanine floor as an example,using PKPM and SAUSAGE software to make the original design plan of the structure(the mezzanine floor is a cast-in-place reinforced concrete structure,that is,the floor and the wall columns are just connected)The seismic performance analysis and various evaluations have been carried out.The calculation results show that the lateral stiffness of the bottom of the structure is irregular due to the large opening of the sandwich floor and the sudden change in the shear bearing capacity of the sandwich layer has become a weak layer defined by the code.The original plan is not advisable.Two solutions are proposed for this problem.Option 1: The mezzanine floor adopts a lightweight composite beam-slab structure,and the light-weight composite beam-slab structure floor is hingedly connected with the vertical wall column components.Option 2: Improve the shear bearing capacity of the interlayer of the original design structure.PKPM software was used to analyze and evaluate the plan one,and the results showed that it was feasible.However,due to the limitation of the software,PKPM adopts the method of direct merging calculation in the analysis.This method does not consider the stiffness contribution of the sandwich floor in the plane and the transmission of the horizontal force.This is different from the actual situation.Really simulate the hinged connection between the mezzanine and the wall column.In order to obtain more accurate and true analysis results,considering the contribution of the in-plane stiffness of the mezzanine floor,in PKPM,the hinged mezzanine is directly established for the composite beam and slab floor in the simplified method of equal stiffness,but the analysis result is still not good.Based on the above situation,in order to obtain more accurate,reliable and true analysis results,it is necessary to adopt more accurate and effective three-dimensional finite element analysis software to ensure that the plan is accurate and feasible.In the actual design analysis,there are three different calculation methods for Scheme 1: 1.Directly and layer calculation;2.Combine and consider the horizontal inertia force at the mezzanine elevation;3.Calculation of the hinged connection between the mezzanine floor and the wall column.Aiming at the problem of sandwich structure,most scholars currently mainly choose the direct layered calculation method to analyze the influence of the sandwich on the structure,which is the same as the method used by the PKPM software for the simulation analysis of Scheme 1.From the above analysis,this method is not the most accurate and effective method in Option 1,and the accuracy of the PKPM software calculation is not good.Based on this,this article will use the non-linear finite element analysis program VFEAP based on the theory of three-dimensional virtual laminated degenerate elements to further demonstrate that the first option is feasible,deeply analyze the three different calculation methods in the first option,and compare and select the best Calculation method.Therefore,the non-linear finite element analysis program VFEAP based on the theory of three-dimensional virtual laminated degenerate elements is introduced,and four groups of refined finite element simulation models are established according to the three different calculation methods of the original scheme and scheme 1.The simulation model performs elastoplastic analysis under the horizontal load in the weak axis direction.By comparing the four sets of model load-displacement curves,stiffness degradation,and shear redistribution,the following conclusions are drawn:Based on the VFEAP program,the three calculation methods of Scheme 1 can all solve the irregular lateral stiffness of the original structure and the shear bearing load of the sandwich.For the problem of sudden force changes,the calculation method that considers the articulation of the mezzanine and the wall column(that is,the calculation method 3 in Scheme 1)is the most accurate and reliable calculation method,which is the most consistent with the actual situation,and is the optimal calculation method.For the second option(improving the shear bearing capacity of the original structure sandwich),PKPM modeling was used for analysis and evaluation,and the results showed that it was feasible.In order to improve the reliability of the structure and supplement the analysis of weak parts,based on the elastic floor analysis of the mezzanine floor,the nonlinear finite element analysis program VFEAP based on the three-dimensional virtual laminated degenerate element theory,considering the space synergy effect of beams,slabs,columns and walls,is established and Scheme 2 The corresponding finite element analysis model and elastoplastic analysis are carried out.Through the analysis of the stress development and deformation effects of the internal reinforcement of the sandwich beams and frame columns,the weak position of the sandwich floor is analyzed,which provides a basis for proposing strengthening measures,and is targeted strengthen.