Analysis On The Seismic Performances Of Super High-rise Structures Affected By Strength Of Concrete In Joint Core

During the seismic design of super high-rise structures, the huge differences ofconcrete strength grade between beams and columns is inevitable. In order to ensure thecapacity of the core joints, the concrete strength of core joints must be the same as theconcrete strength of columns, however the traditional construction method is easy tomake quality problem in the construction, so that the capacity of core joints can’t meetthe requirement of design. If use the construction method of sandwich joints, notonly can guarantee the quality of joint core area construction but also can save time. Butwhen the concrete strength of core joints is the same as the concrete strength of beamslower than concrete strength of columns, the super-high rise concrete structures weathermeet the requirements of "no damage in small earthquake, repairable under moderateearthquake, no collapse under rare earthquake" seismic fortification goal is not clear. Soit has important theoretical value and practical significance by research on the seismicperformances of super high-rise structure affected by strength of concrete in joint core.In this paper, using the finite element analysis software MIDAS/GEN, establish themodel that the concrete strength of core joints is the same as the concrete strength ofbeams (model1), simulates the super-high rise concrete structure that use theconstruction method of sandwich joints, establish the model that the concrete strength ofcore joints is the same as designs (model2), simulates the super-high rise concretestructure that use traditional construction method. Response spectrum analysis, pushover analysis and the theoretical analysis of the seismic bearing capacity of core joints.The main contents of this paper are:(1) Through response spectrum analysis, read the results of the two models likefirst6vibration, the period, cycle ratio, the ratio of stiffness to weight. The resultsindicate that the two models. but the model1indicators are higher than model2, showsthat after the concrete strength of core joints decreases, the vibration the period, cycleratio, the ratio of stiffness to weight will increases a little. So the concrete strength ofcore joints has little effect on the seismic performances of super-high rise structure.Read stress and shear stress of the core joints of the response spectrum analysis, If theconcrete strength of core joint decreases, bottom floors which under the largeraxial pressure, floors that column section changes have the condition that the compressstrength and the shear strength of the column changed floor are not enough. (2) Analyzed the elastic and plastic action of the model under seldom occurredearthquake. Read the displacement, base layer shear, inter story displacement angle,plastic hinge state in the performance point from these two model. The results show: theinter story displacement angle at performance point from the model1and model2canmeet the limits value of the standards requirements; but as the grade of core areaconcrete decreased, inter story displacement angle will increase, base shear force willdecrease slightly. If the concrete strength of core joints decreases too much, it will leadthe plastic hinge of failure state occur in the structure.(3) According to the formula in the standard or the reference, combined with thecolumn axial force analyzed from the response spectrum analysis in the third chapter,this paper calculated the compression capacity and horizon shear capacity of the typicalnodes, analyzed the impact of changes of concrete strength on the bearing capacity ofsuper high building structure nodes. The result indicate that the changes of the concretestrength grade has a significant impact on axial compression capacity and horizon shearstrength capacity, the more strength grade decreased, the more axial compressioncapacity and horizon shear strength capacity decreased.