Experimental Study Of Full-Scale RC Hollow Floor With Beam Web Openings Under Normal Service Limit State

At present,scholars at home and abroad have conducted a lot of experimental and theoretical studies on the mechanical properties of concrete hollow floors and concrete beams with openings,and they have been widely used in engineering.However,there are few studies on the mechanical properties of concrete hollow floors with beam web openings,especially on the cross-sectional geometric properties(moment of inertia and effective tensile concrete cross-sectional area,etc.),cracking properties,strain and deformation of concrete hollow floors with beam web openings under normal service limit state.Therefore,this thesis carries out experimental studies on the mechanical properties of full-scale steel mesh box hollow floor(SMB floor)and concrete assembled box hollow floor(CAB floor)under short-term load under normal service limit state,and carries out related finite element simulation and theoretical studies,mainly as follows:(1)The mechanical performance tests of SMB and CAB floors were carried out to obtain the crack distribution,maximum and average crack widths,concrete strain and displacement of the two hollow floors under short-term load,and to compare and analyze the results with the related test results at home and abroad.The results show that the maximum crack width of each member of SMB and CAB floors exceeds0.20 mm,while the mid-span displacement of the floors does not reach 1/250 of the calculated span;the crack distribution at the bottom of the slab of both concrete hollow floors with beam web openings is "cross-shaped",and there are obvious diagonal cracks at the rectangular holes at the bottom of the slab.Comparing the test results of the two hollow floors,it can be seen that increasing floor thickness or the height of the edge beam can effectively reduce the crack width and the span displacement of the floor.(2)Based on ABAQUS software,a computational model of concrete hollow floor with beam web openings was established and compared with the test results of displacement,crack and strain of hollow floor under normal service limit state,and the influence law of hole height,hole eccentricity,rib spacing,edge beam height(beam slab stiffness ratio),floor thickness(span height ratio),rib beam width(aspect ratio)and the thickness of the cast-in-place layer at the top of the slab(cast-in-place layer at the bottom of the slab)on the mechanical mechanism of concrete hollow floor with beam web openings was studied.The results show that the hole height,hole eccentricity,edge beam height(beam slab stiffness ratio)and floor thickness(span height ratio)have a significant impact on the local tensile damage and stress-strain of the bottom of the slab,the edge beam with openings.The height of the opening should not exceed 0.43 times the height of the beam.The opening should be located in the compression zone,with a rib spacing range of 0.15～0.18 times the calculated span,and the number of rib beams should be even.The stiffness ratio of beams to slabs should be between 1.5～3.0,and the span to thickness ratio should be between 18～23.(3)Based on the proposed slab method,cross-beam method and table check method,etc.,considering the influence of the hole on the flexural stiffness of the rib(edge)beam section and the effective tensile concrete cross-sectional area,the calculation unit of the rib(edge)beam section form in the concrete hollow floor is established,and three calculation unit analysis conditions are proposed and compared with the span displacement,rib(edge)beam crack width of the test hollow floor.The results show that the calculated displacement of the proposed plate method agrees better with the test results compared with the cross-beam method and the table check method,in which the T-shaped(inverted L-shaped)section should be used for the calculation unit of the flexural stiffness of the abdominal open rib(side)beam section.In addition,when analyzing the crack width of the hollow floor abdominal open rib(side)beam,the lower chord is selected as the calculation unit,and its effective tensile concrete cross-sectional area calculation should consider the influence of the lower flange,and the stress of the tensile reinforcement should be calculated according to the eccentric tensile member.This thesis has 81 figures,13 tables and 96 references.