Identify The Slab Enhancement Effect To Reinforced Concrete Beams By Elastic And Inelastic Analysis

Chinese seismic code uses principle of "capacity design” to ensure the seismicperformance in stronger earthquake of structures that were designed according to thefrequent earthquake action. The "strong column weak beam" which is one of the seismicmeasures is one of the applications in engineering design of the principle of "capacitydesign”.The "strong column weak beam" is to guide frame structures to form stabileplasticity energy dissipation mechanism after yielding which owns good seismicperformance, and to avoid forming layer lateral sway system which is resulted in all thecolumns in same floor with plastic hinge in its end. However, the actual seismic hazardshowed that almostall the RC frame structures which were suffered from differentdegree of damage or destruction formed plastic hinge in columns’ end.Cast-in-placeslab’s reinforcements which parallel to the longitudinal beam will be involved inresistance to the negative bending moment, this makes the currentdesign method whichdoesn’t contain slab in analysis badly underestimate the beam’s actual ability to resistnegative bending moment at its end, and this is one of the important reasons that the"strong column weak beam" can’t achieve its purpose.Many researchers at home and abroad put experiments or simulation analysis onthis issue, they put forward that the effective flange width can be used to quantize slabenhancement effect to reinforced concrete beam,but the suggestions of effective flangewidth are not the same. Some of these studies were about experiments or simulationanalysis of beam-column-slab connections,however, connection doesn’t have theboundary constraint of slab in actual frame structure, so these researches are unavailablefor quantizingslab enhancement effect to beam. Amongthe studies of frame structure,only a small number of researchers using test or elaborate inelastic simulation analysisby three-dimensional entity element,but the suggestions of effective flange width weremade by these researchers are not considerate, because they didn’t consider enoughtypes of connection or influence of factors such as beam span and section height. Atpresent, the effective flange width for engineering design is not unified, the problem isstill in research stage.With the actual situation, this paper adopts elaborate elastic and inelastic method toanalyze frame structure which is subject to horizontal load with three-dimensional entity element (simulated concrete) and three-dimensional truss element (simulated reinforced)on the basis of reading a large amount of reference.Main work and achievements of thispaper are briefly as follows:①The elastic analysis of one-story and single span space RC frame structures withand without slab have been conducted utilizing ABAQUS, and the contrast of the resultshas been made.The results show that the cast-in-place slab enhances the ability of framestructure to resist horizontal displacement, and enhances the longitudinal beam’sbending rigidity and bending strength. Change the slab thickness, the concrete strengthgrade, the longitudinal beam stiffness and transverse beam stiffness of the framestructure with slab, then comparing slab reinforcement strain with original structure tostudy influence of these factors. The conclusionis that longitudinal beam stiffness is thelargest degree of influence on floor participating in resisting negative bending moment,followed by the transverse beam stiffness, again is the thickness of the floor slab, finally,the concrete strength grade (only improve one level), and the way of influence of thesefactors are also different.②The inelastic analysis of one-story and single span space RC frame structureswith and without slab have been conducted utilizing ABAQUS, and the contrast of theresults has been made.The results show that the cast-in-place slab enhances the abilityof frame structure to resist horizontal displacement, and enhances the longitudinalbeam’s bending rigidity and bending strength, particularly, enhances the flexuralstrength of beam in hogging moment area, and this enhancement effect is moreobviousat the time when the inelastic degree of structure is deeper.So, the impact ofCast-in-place slab on beams and the whole structure cannot be ignored.③For one-story and single spanspace frame structure with slab, put detailed studyon transverse distribution of slab reinforcement stress under different horizontaldisplacement of structure.The conclusion is that the stress of slab reinforcement isdecreasing with the distance being far from longitudinal beam,the stress of slab topreinforcement is larger than slab bottom reinforcement as a whole,the stress of slabreinforcement on the whole increases with the growth of structure’s horizontaldisplacement, when the interlayer displacement angle of structure is1/35, the stress ofslab reinforcement on the whole tends to be stable.④The analysis work has began with the space frame structure of one-story with asingle span, then developed to a space frame structure of one-story with two spanswhich contains much more kinds of joints, and lastly to a space frame structure of two-story with two spans including all kinds of joints, then get the distributionregularities of slab reinforcement stress of different kinds of joints in differentstructures.The contrast of theseregularities shows that the type of joints is greaterinfluence on the stress value and distribution of slab reinforcement, that is to say, thetype of joints is bigger influence on the effective flange width, so theanalysis modelshould be selected for the structure which includes comprehensive type of joint.⑤For space frame structure of two-story with two spans, the longitudinal beam’sspan and height of the cross sectionis altered to study they impact on effective flangewidth. Results indicate that the effective flange width increaseswith the growth of thelongitudinal beam span; the impact of longitudinal beam’s section height on effectiveflange width is not regular. So, the longitudinal beam span is selected as a basicparameter to describe the effective flange width of each joint when the interlayerdisplacement angle of structure is1/35.