【作者】 陈才华；

【导师】 王翠坤；

【作者基本信息】 中国建筑科学研究院有限公司 ， 结构工程， 2020， 博士

【摘要】 高层建筑已经成为我国量大面广的最主要的建筑形式,而框架-核心筒结构是我国高层特别是超高层建筑最主要的结构形式。抗震概念设计要求框架-核心筒结构的框架应具备合理的刚度和承载能力,中外设计规范均有加强框架的相关规定。我国设计规范和超限审查技术要点通过控制框架分担最小剪力比(框剪比)和框架剪力放大来增强框架的刚度和承载力,已有研究成果表明,这对提高框架-核心筒结构的抗震安全性有重要的作用。但框剪比及其限值的规定基于定性化的抗震概念,定量化的研究成果不足,成为近年来国内高层建筑结构设计的一个热点问题。本文针对这一问题,从框架-核心筒结构双重体系协同工作原理和抗震二道防线出发,通过采用基于线弹性的连续化理论分析、基于弹塑性的静力推覆分析和增量动力时程分析,对框架-核心筒结构框剪比指标的物理意义、分布规律、影响因素、变化规律以及对整体抗震性能的影响等开展了系统的研究。主要工作内容和结论如下:1.基于双重抗侧体系协同工作原理,采用连续化方法推导建立框架-核心筒结构等刚度条件下考虑弯剪耦合效应以及变刚度条件下的基本微分方程组并求解,借助有限元分析结果验证了方程推导正确、求解结果准确。连续化分析结果表明:为了保证框架-核心筒结构双重抗侧体系充分发挥协同工作效应,必须保证框架具备一定的刚度;框剪比指标可以定量反映框架与核心筒之间相对刚度的大小,规范采用“框剪比”这一指标是合理有效的,其本质为限定框架与核心筒相对刚度的比值(刚度特征值)不宜过小。高层尤其是超高层框架-核心筒结构刚度沿高度变化,导致框剪比曲线沿高度分布呈现“中部大、两端小”的特点,可采用“最大框剪比”来限定框架与核心筒的相对刚度,放松顶部楼层框剪比限值。2.基于整体抗侧刚度相近的原则,分别设计了9个和12个外框与核心筒具有不同刚度比(框剪比)的模型,利用Perform3D软件进行静力弹塑性分析,对比研究不同模型的塑性发展过程和框剪比变化规律。分析表明:随着结构进入塑性,内力会在核心筒剪力墙和框架之间重分布,框剪比曲线的变化存在两种模式,且仅由框架与核心筒弹性状态的刚度比(框剪比)决定;当弹性分析的最大框剪比大于5%时,其变化规律为“先增大后减小”,当弹性分析的最大框剪比小于5%时,其变化规律为“一直增大”;前者内力重分布的过程体现了双重体系的优势,二道防线作用充分发挥,后者二道防线作用有限,整体性能接近于单重抗侧体系。从抗震二道防线角度,框架-核心筒结构双重抗侧体系的框架应具备一定的刚度,本文的算例模型分析结果表明,“弹性分析的最大框剪比大于5%”可作为框架的最低刚度要求。3.基于整体抗侧刚度相近的原则设计了5个不同框剪比的框架-核心筒模型(含一个单重抗侧体系),利用ABAQUS软件进行增量动力时程分析(IDA),对比不同模型的动力推覆曲线、塑性发展和损伤、框剪比与框架倾覆力矩占比变化、刚度退化、倒塌概率和倒塌储备系数,研究框剪比对整体抗震性能的影响。分析表明:相同输入条件下,双重体系的抗震性能优于单重体系;框剪比越大的模型,其墙体损伤越小,刚度退化越缓慢,延性越好。在设防大震下,经过合理设计的单重抗侧体系和不同框剪比的双重抗侧体系均可以到达预定的性能目标要求;但随着地震强度的进一步增加,当峰值加速度超出设防烈度大震较多时,双重体系结构具有更高的抗震冗余度;且框剪比越大的模型抗震冗余度更高。结构倒塌储备系数随着框剪比增大而增大,单重抗侧体系的倒塌储备系数明显低于双重抗侧体系。4.IDA分析表明,随着峰值加速度增大,框架分担的倾覆力矩占比逐渐增大;且框剪比越大的模型框架倾覆力矩占比增长越多。在设防大震下及超设防大震作用下,单重体系模型倾覆力矩基本由核心筒承担,双重体系模型外框分担的倾覆力矩增大较多,发挥了重要的抗倾覆作用,从而延缓整体结构的刚度退化。单重体系模型的平均框剪比曲线和平均框剪比最大值均呈现“一直增大”的状态,双重体系模型呈现“先增大后减小”的状态,框剪比的变化模式反映了单重体系和双重体系的区别。基于底层框架倾覆力矩占比以及框剪比的变化模式,本文的算例模型分析结果表明,弹性分析时最大框剪比大于5%的框架-核心筒模型,其框架刚度可以满足双重抗侧体系抗震二道防线的要求。5.提出了框架-核心筒结构基于动力作用下刚度退化的整体抗震性能评价指标——“刚度退化系数”,其定义为结构各阶平动刚度的加权平均刚度退化率,并通过两个实际工程缩尺模型振动台试验进行验证。利用该指标对5个框架-核心筒模型进行抗震性能评价和比较,结果表明:模型的刚度退化系数随着峰值加速度的增加而增加;在设防大震及超设防大震作用下,单重体系模型的刚度退化系数明显高于双重体系模型,且框剪比越大的模型刚度退化系数越低;证明双重体系的抗震性能优于单重体系,框剪比越大的模型抗震冗余度越高。6.弹塑性动力时程分析表明,大震下框架-核心筒结构发生内力重分布,框架应具备一定的强度(承载力)承接从核心筒转移的地震力。以四个双重体系框架-核心筒模型为例,对现行中美规范的框架剪力调整方法进行了比较分析,并分别基于弹塑性时程分析和基于等效线性化分析提出了两种实用的框架剪力调整方法。更多还原

【Abstract】 High-rise buildings have become the most common building form in China,and framecore tube structure is the main structure form of high-rise buildings,especially super high-rise buildings.The seismic conceptual design requires that the frame should have reasonable stiffness and bearing capacity in the frame-core tube structure,and it also should be strengthened according to Chinese and foreign design codes.The stiffness and bearing capacity of the frame are enhanced by controlling the minimum frame-shear ratio and the frame shear amplification according to Chinese design code and technical points of expert peer review.The existing research results show that this plays an important role in improving the seismic safety of frame-core tube structures.However,the regulation of frame-shear ratio and its limit value is based on the qualitative seismic concept rather than the quantitative research results,which has become a hot issue in the structural design of high-rise buildings in recent years.Aiming at this problem,base on the cooperative working principle of dual system and the secondary aseismic system,the physical significance,distribution law,influencing factors,variation rules of frame-shear ratio and its influence on the overall seismic performance of frame-core tube structure are systematically studied by using the continuum analysis,static pushover analysis and incremental dynamic time history analysis.The main contents and conclusions are as follows:1)Based on the cooperative working principle of dual system,the basic differential equations of frame-core tube structure with uniform stiffness considering bending shear coupling effect and nonuniform stiffness are established by using continuum analysis method and solved by numerical method.The derivation and solution of the equations are verified by finite element analysis.The results show that: the frame should have reasonable stiffness to ensure adequate cooperative effect of dual system in frame-core tube structure;the frame-shear ratio index can quantitatively reflect the relative stiffness between the frame and the core tube,and it is reasonable to adopt the frame-shear ratio in Chinese design code.The essence of this limit is to ensure the relative stiffness ratio(stiffness characteristic value)between frame and core tube should not be too small.For high-rise especially super high-rise frame-core tube structure with nonuniform stiffness,the distribution of frame-shear ratio curve along the height presents the characteristics of "large in the middle and small at both ends".The "maximum frame-shear ratio" can be used to ensure the relative stiffness of frame and core tube,and the limit value of frame-shear ratio on top floors can be reduced.2)Based on the principle of equal stiffness,9 and 12 frame-core tube models with different stiffness ratio(frame-shear ratio)were designed.The static pushover analysis of these models were carried out by using perform3 d software,and the plastic development process and variation rule of frame-shear ratio were compared.The analysis shows that: the internal force redistributes between the core tube and the frame with the plastic development of the structure,and the change of frame-shear ratio curve exhibits two modes which determined by the stiffness ratio(frame shear ratio);when the initial maximum frame-shear ratio is greater than 5%,the change rule is "first increase and then decrease",and when the initial maximum frame-shear ratio is small than 5%,the change rule is "always increase";the former reflects the advantages of the dual system which give full play to the secondary aseismic system in the process of internal force redistribution,and the overall performance of the latter is close to the single system without the secondary aseismic system.From the point of secondary aseismic system,the frame should have reasonable stiffness in frame-core tube structure,and the initial maximum frame-shear ratio must be greater than 5% base on the results of models in this paper.3)Based on the principle of equal stiffness,five frame-core tube models with different frame-shear ratio(including a single system)are designed.The incremental dynamic time history analysis(IDA)is performed by ABAQUS software.The dynamic pushover curves,plastic development and damage,variation rules of frame shear ratio and frame overturning moment ratio,stiffness degradation,collapse probability and collapse margin ratio of different models are compared and the influence of frame-shear ratio on the overall seismic performance is studied.The results show that: under the same input conditions,the dual system exhibits better seismic performance than the single system;the model with larger frame-shear ratio exhibits smaller wall damage,slower stiffness degradation and better ductility.Under the precautionary rare earthquake,the single system and the dual system with different frame-shear ratio can reach the predetermined performance requirements;however,with the further increase of earthquake intensity,the dual system has higher seismic redundancy and the model with larger frame-shear ratio exhibits higher seismic redundancy.The collapse margin ratio of the structure increases with the increase of the frame-shear ratio,and the single system has significantly lower collapse margin ratio than the dual system.4)The IDA results show that: with the increase of peak acceleration,the proportion of overturning moment shared by the frame gradually grows and increases more for model with larger frame-shear ratio.Under the precautionary and over precautionary rare earthquake,the overturning moment of the single system model is basically born by the core tube,and that shared by the outer frame of the dual system model increases more,which reveals the outer frame plays an important role in anti-overturning,thus delaying the stiffness degradation of the whole structure.The change of the curve and the maximum value of average frame-shear ratio exhibits two modes with "always increase" for single system and "first increase and then decrease" for dual system,which reflects the difference between the single system and the dual system.According to the change mode of the proportion of overturning moment shared by the frame of the bottom floor and the frame-shear ratio,the frame stiffness with the maximum frame-shear ratio greater than 5% can meet the requirements of the secondary aseismic system of the frame-core tube structure base on the results of models in this paper.5)The overall seismic performance evaluation index of frame-core tube structure based on the stiffness degradation under dynamic action is proposed as "stiffness degradation coefficient",which is defined as the weighted average stiffness degradation rate of the horizontal dynamic stiffness of each order of the structure,and is verified by shaking table tests of two scale models.Five frame-core tube models are evaluated and compared by that index,and the results show that: the stiffness degradation coefficient increases with the increase of the peak acceleration.Under the precautionary and over precautionary rare earthquake,the stiffness degradation coefficient of the single system model is significantly higher than that of the dual system model,and the model with larger frame-shear ratio has lower stiffness degradation coefficient.It’s proved that the dual system exhibits better seismic performance than the single system,and the model with larger frame-shear ratio has higher seismic redundancy.6)The elastic-plastic dynamic time history analysis shows that the internal force of the frame-core tube structure redistributes under the strong earthquake,and the frame should have a certain strength(bearing capacity)to undertake the seismic force transferred from the core tube.Taking four dual system frame-core tube models as examples,this paper compares and analyzes the frame shear adjustment methods in current Chinese and American codes,and puts forward two practical frame shear adjustment methods based on elastic-plastic time history analysis and equivalent linearization analysis respectively.更多还原