Study On Elasto-plastic Analysis Method And Seismic Behavior Of Hybrid Tall Building Structures

Focusing on the seismic performance of hybrid tall building structures, two aspects of study, elasto-plastic analysis method and shaking table test of frame-core tube model, have been carried out in this dissertation. The main research contents and results are as follows:1. After summarizing and comparing the Existing uniaxial stress-strain models of concrete, a model which can calculate the damage and stiffness recovery effects during cyclic loading is presented, and based on which user material subroutines UMAT and VUMAT have been developed through the interface of ABAQUS program. These two subroutines can be used in conjunction with implicit and explicit solver respectively to analyze the nonlinear behavior of beam column members with fiber model.2. The related issues and techniques in static nonlinear analysis using explicit dynamic solver have been discussed. The push-over analysis of a pseudo-static test model structure has been carried out by using the ABAQUS damaged plasticity model for concrete and the user material subroutines developed. The analysis results agree well with the loading process of test, which shows the validity in the elasto-plastic analysis of hybrid tall buildings by using the ABAQUS damaged plasticity model and the user material subroutines.3. 1:15 scale model of a 30 storey frame-core wall hybrid structure with main material mortar was designed and built. The shaking table test of this model has been carried out in the seismic lab of CABR. The similarity ratio of acceleration is 1:1,and the model experienced the action of the single-direction seismic wave with the amplitude from 70gal to 620gal. The test results indicate that the frame-core wall hybrid structure model has performed almost with a elastic behavior under the action of seismic wave of moderate earthquake with the intensity of VIII. The final failure mode of the structure is overturn, the bottom of the core-tube is pulled out. The related issues, such as dynamic response, free vibration characteristics, structure deformation and stress in member sections have been studied through the experimental results. The problems of the existing design method have been pointed out and the corresponding suggestion for design have been put forward.4. A group of members with the same section and height of the columns in the first floor of the above shaking table test model have been tested under low cyclic reversed loading with different axial compression ratio, the hysteresis loops and the relation line of ultimate axial force and bending moment have been obtained. It can be indicated from the test that the failure modes of these members can also be divided into tensile failure and compressive failure. The shape of relation line is similar to that of the prototype members. The yielding axial compressive forces and yielding bending moments with and without axial force satisfy the similarity conditions approximately.5. A stress-strain curve has been fitted for the mortar in the shaking table test model based on the material properties data. Elastic and Elsto-plastic time history analysis of the above model in the shaking table test have been done. The calculated results show that the user material subroutines realize the stress-strain relationship of the mortar and the stiffness degradation and stiffness recovery effects during cyclic loading have been well simulated. The analysis results agree well with the test results during elastic phase. The analysis ignored the damage cumulation between different analysis cases, hence the calculated displacement of the subsequent cases is less than that of the test, but the analysis results reflect the main characteristics of the loading process of the test and the calculated dynamic skeleton curve agree well with that of test.6.An overall comparison between the pseudo static test in Ref. 37 and the shaking table test above is given. It is shown that the failure modes and the characteristics of structure stress and deformation of two tests are approximately the same. The static and dynamic skeleton curves of the prototype model remain linear elastic under the action of moderate earthquake, the experimental similarity conditions agree very well during the elastic phase in both tests. In the plastic phase, the dynamic skeleton curve is higher than the static skeleton curve, the overall damage of shaking table test is slighter than that of the pseudo test. There is serious damage in the frame columns at the top of the model in the shaking table test, which is obviously different from the pseudo test.7. The base shear and the overturning moment distribution between the bottom frame and core tube have been discussed based on the static and dynamic analysis results. It is indicated that the frame carries a very little portion of base shear during elastic phase and this portion increases during the plastic phase, the frame is the second line of defense to the shear. On the other hand, the overturning moment carried by the frame is comparable to that of the core tube, whether during elastic phase or plastic phase, the frame is not only the seconcd line of defense to the overturn failure.