Study On The Effects Of Story Height Variations To Seismic Performance Of High Rise Reinforced Concrete Frame-Core Wall Structures

Over the past twenty years, China has become the main areas of the construction of high-rise buildings in the world. Accompanied by the rapid growth of the number, the somatotype and function of high-rise buildings are getting more complex and more diverse. Even in a same high-rise building, floor height along the building height direction would change due to the requirements of the functional layout of buildings. The lateral stiffness of irregular phenomena caused by local floor height mutation becomes very common and prominent for high-rise building structure.In this dissertation herein, the study was carried out by focusing on the effects of local story height variations towards the frame-core wall structure, one of the most popular structural systems for high rise buildings in China. The measurement method and control indicators of lateral stiffness regularity for frame-core wall structure, the impacts of story height variation towards structural deformation morphology, force patterns, yielding mechanism and failure mode under intensive earthquake acting were emphasized to investigate and discuss. The main research work and creative results were as follows:1) The increasing of local story height will decrease the lateral stiffness of the corresponding story and whole structure, lead to forces and deformations amplified and concentrated at individual story, change the stress pattern, yielding mechanism and failure mode of structural members and harm structure aseismic performance in consequence.The results of numerical analysises and large scale shaking table tests research show that:the higher magnitudes and the more sudden changes in story height would cause greater amplification and heavier concentration of story displacement, inter-story drift angle, shear force and overturning moment at the corresponding story. And such amplification and concentration will increase in nonlinear relationship as the ground motion increasing. Moreover, the story height increase would reduce frame’s the lateral stiffness and the its relative ratio to core wall’s, decease the seismic action undertaking proportion of frame, the bearing capacity redundancy even the yielding mechanism and failure mode of structural members.2) The rule of control the lateral stiffness regularity of structure is one of the key measurements to guarantee the seismic safety of structure. Base on the study of this thesis, the author recommended adopting the relative ratio of story shear to inter-story drift angle to adjacent story as the measurement method for evaluating the regularity of story lateral stiffness for frame-core wall structure. The author also proposed the story stiffness ratio limitation indicators for different locations of story, the first story should not be less than1.5and shall not be less than1.4; the other stories should not be less than1.1, should not be less than0.9when the story height is over1.5times larger than the below’s.3) When adopting the recommended method and proposed limitation value for evaluating the regularity of story lateral stiffness for frame-core wall structures, the seismic forces of structural members should be enlarged with no less1.25to improve their bearing capacities. The reinforcements should be enlarged directly when amplifying seismic forces cannot increase the reinforcements effectively.4) The results of numerical analysis and shaking table test showed the tension effect in structure bottom; especially the core wall is heavily for high rise frame-core wall structure under intensive earthquake acting. The increase of story height would aggravate such situation. The core wall would tend to be tension-flexural failure mode. The structure designer should pay more attentions on keeping the continuity of the member and the reinforcement and the validity of anchorages.5) The member bearing capacity redundancy method proposed in this dissertation gives the explicit expression of the internal connections between the story lateral stiffness, the member force and the yielding mechanism (failure mode) and reveals the essential characteristics of the effects of local story height increase towards the yielding mechanism, failure mode of structure members and the overall structure aseismic performance.6) The time history dynamic analysis shows that the increases of upper story’s height will increase the high mode effects and the story shear force, overturning moment and inter-story drift angle would be larger than those of response spectrum analysis. Additional time history analysis should be taken for cover the deficiency of response spectrum analysis.