| With the shortage of land for urban construction,the existing residential areas are set up with basement parking lots or basement shopping mall buildings.In order to meet the requirements of greening and environmental protection,the top surfaces of these underground buildings are generally covered with planting soil to plant trees and flowers,and the thickness of the covering soil is generally 0.6-2.5m.The structural system of currently popular underground buildings in China usually adopts cast-in-place reinforced concrete frame structure.When the greening planting soil is installed on the roof of the reinforced concrete basement,according to the requirements of the building waterproofing regulations,in order to prevent the roof leakage from affecting the use of the building,the floor thickness of the basement roof in contact with the soil should not be less than 250 mm.Due to the large thickness of the roof of the under-covering room and the high bearing capacity of the floor,the frame beams are often set instead of secondary beams in the project,thus becoming reinforced concrete frame beam-large panel structure.Due to the rapid construction speed of this structural system,it has been widely used in the basement structure in China.The cast-in-place reinforced concrete frame-large panel structure has a thick floor,and the structural reinforcement has a big difference from the general frame structure with a thickness of about 100 mm.In addition,the ratio of the effective height of the slab as the flange to the beam is generally greater than 0.1,which exceeds the requirements of the concrete code.At present,in actual engineering structure design,one of the following two methods is usually adopted beam-slab isolation method and beam-slab composition method.The beam-slab isolation method is a traditional method of floor slab stress analysis.When calculating the design slab,the beam is regarded as a support with no vertical displacement of the floor to calculate the reinforcement,deflection and cracks of the floor.When calculating the design beam,According to the traditional two-way slab transfer mode,the load of the floor slab is simplified into a triangular distributed load or a trapezoidal distributed load on the beam to calculate the beam reinforcement,deflection and cracks.This design method ignores the joint work of the beam and the plate.The beam-slab composition method is a finite element analysis method that considers the joint work of the beam and the plate.In the structural calculation and analysis,the beam is used to simulate the beam element and the floor slab shell element.Calculation of plate reinforcement,deflection and cracks.Since the two design calculation methods are very different in the reinforcement of beams and slabs,in the first method,the floor slab does not directly transfer the load to the column,and all the loads are transferred from the beam to the column,so the beam reinforcement is large and the plate reinforcement is small;When the second method is adopted,because the thickness of the floor slab is close to the requirement of a beamless floor,the load directly transmitted through the floor to the column is large,so the load transmitted from the slab to the beam and then from the beam to the column is relatively small,so the beam The reinforcement is small and the plate reinforcement is large.Because the calculation results of the beam and plate reinforcement obtained by these two calculation methods are very different,designers often have no idea,and designers often argue over this,causing great confusion.So,the correct and reasonable design of reinforced concrete frame beam-large panel structural system with a floor thickness of not less than 250 mm is one of the engineering problems urgently to be solved in China's engineering design community.This paper analyzes and studies this issue.This paper first uses the large-scale general-purpose software SAP2000 and the most commonly used building structure design software YJK in China's engineering design to design the reinforcement of a typical basement structure with a span of 8.1m and a scale of 3x3.Among them,SAP2000 model beam adopts BEAM unit,slab adopts SHELL unit,and YJK model adopts beam-slab isolation method.By changing the thickness of the floor slab,the beam-slab isolation method and the beam-slabcomposition method are separately used to obtain the reinforcement data of the beam slab column.Then use the large-scale general finite element software ABAQUS,the concrete uses solid elements,and the steel elements use linear elements to perform elastoplastic simulation analysis to analyze the impact of the frame beam and floor slab when the beam and plate are divided and the beam and plate are combined when the thickness of the cast-in-situ floor slab is changed.Force deformation mechanism.The following conclusions are obtained:(1)The ABAQUS finite element analysis of the beam-slab-column reinforcement data obtained from the beam-slab isolation method and beam-slab composition method respectively shows that The ultimate bearing capacity of the beam-slab isolation method reinforcement is greater than that of the beam-slab composition method.(2)Under normal load,ABAQUS finite element analysis is performed on the beam-slab-column reinforcement data obtained from the beam-slab isolation method and beam-slab composition method.The results show that: the beam reinforcement stress of the beam-slab isolation method is small,and the slab support reinforcement stress is small,The stress of the steel bar in the middle of the slab is large;the stress of the steel bar of the beam reinforced by the beam-slab composition method is large,the stress of the steel bar of the slab support is large,and the stress of the steel bar in the middle of the slab span is small.Beam-slab deflection of beam-slab isolation method is less than beam-slab deflection of beam-slab composition method.(3)Under ultimate load.ABAQUS finite element analysis is performed on the beam-slab-column reinforcement data obtained from the beam-slab isolation method and beam-slab composition method.The results show that: the beam reinforcement stress of the beam-slab isolation method is small,and the slab support reinforcement stress is small,The stress of the steel bar in the middle of the slab is large;the stress of the steel bar of the beam reinforced by the beam-slab composition method is large,the stress of the steel bar of the slab support is large,and the stress of the steel bar in the middle of the slab span is small.Beam-slab deflection of beam-slab isolation method is less than beam-slab deflection of beam-slab composition method.(4)The recommended formula for the effective flange width of the frame beam span specified in "Code for Design of Concrete Structures" GB50010-2010 is only applicable to the general beam-slab structure,not to the frame beam-large slab structure.Corresponding to the ABAQUS model,the effective flange width in the improved beam span is analyzed. |
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