The Research On The Macroscopic Finite Element Theory Applied To The Steel Reinforced Concrete Frame Structure

Due to the high rigidity, high bearing capacity, superior seismic performance and otheradvantages, SRC composite structures become the preferred structures used in the high-rise,long-span, heavy-load and towering structures in high intensity security areas. Because theexperimental data collected from tests generally has larger discreteness and is not enough tohave statistical significance, the research method combining theoretical analysis and numericalsimulations to explore the relevant scientific problems is feasible recently. Considering thecomplexity of the numerical simulation modeling process based on the microscopic element,the high computation cost and the strict requirements to computer hardware, the finite elementnumerical analysis on the nonlinear mechanical behavior of large complex structures is hard toconduct. Under the help of macroscopic element, the effective control of computation cost canbe realized with the finite element numerical analysis in the premise of ensuring calculationaccuracy, which is popular in the large number of research workers.To meet the needs of the research on the macroscopic mechanical behavior of SRC framestructure, the numerical simulation of the bond-slip between materials is realized by modifyingthe strain of steel fiber in the fiber level, based on the fiber element model theory and combinedwith the research results from the previous performance test of the bond-slip between steel andconcrete in our team. The strongly nonlinear mechanical behavior of components is reflectedmore accurately. At the mean time, the shear block model used to simulate the sheardeformation of the SRC joints is proposed. And combined with the latest2D element theory atpresent, the SRC joints element is built. Based on the platform of OpenSEES software, themacroscopic finite element calculation model applied to SRC frame structure is established andis verified well. The main research work and research conclusion are as follows:1. The numerical simulations analysis on the seismic performance of SRC columns using macroscopic element and microscopic element is conducted respectively. And combined withthe measured data of tests, the advantages and disadvantages between the macroscopic finiteelement numerical simulation and the microscopic finite element numerical simulation in theelement principle, the material constitutive, the meshing means, the load control, the simulationresults and other aspects are explored. The refined modeling method applied to beam-columncomponents based on the macroscopic element is put forward, which lays the foundation toimplement the research on the macroscopic finite element theory applied to the SRCbeam-column components in deep.2. The previous research results in our team show that the bearing capacity of componentsis changed a lot after the bond slip of SRC components have occurred. Based on the fiberelement model theory, the numerical simulation of the bond slip between materials is realizedby modifying the strain of steel fiber in the fiber level, according to the bond-slip constitutivemodel of steel concrete and the variation rule of bond slip along the section height proposedpreviously in our team. The significance of this method lies in that the nonlinear mechanicalbehavior of SRC components is reflected accurately.3. In order to detect the delivery mode and the distribution of the inner stress in SRC joints,the insufficiency that the distribution patterns of the inner stress in joints cannot be observedthrough the test is made up with the simulation of microscopic finite element. The sheardeformation of the middle joints, side joints, corner joints and middle joints on the roofinvolved in SRC plane frame is analyzed. It is showed that the inner stress in joints is mainlydistributed in the steel webs of the joint core area, the oblique compression concrete columns inthe steel flange and the inclined concrete columns area restrained with stirrups out of the corezone, which provide the analysis basis to establish the shear transfer formula.4. The shear block model used to simulate the shear deformation of SRC joints is putforward. And combined with the latest2D element theory at present, the SRC joints element isbuilt. According to the construction features of SRC joints, the delivery mode and thedistribution of the inner stress, it is considered that the shear of SRC frame beam-column jointis beard with three parts as steel webs of the joint core area, the internal oblique compressionbar and the external oblique compression bar. Combined with the nonlinear constitutive modelof main construction materials, the shear transfer formula of SRC joints is proposed. Thecoefficient to adjust the width of the oblique compression bar is obtained with the test. The shear block model used to simulate the shear deformation of SRC joints is established finally.Then the shear block model to be called by2D joints element is compiled into the calculatingprograms with C++computer language. Then the numerical simulations of SRC joints elementis realized.5. Combining the method that simulate SRC beam-column by using fiber element with theSRC beam-column joint element, the macroscopic finite element calculation model of SRCframe is established based on the platform of OpenSEES software. Comparing the test resultswith the simulation results, it is showed that the mechanical response of SRC frame subjected tocycle loading is simulated well with the SRC frame model set up in the paper.