NUMERICAL ANALYSIS OF BOND-SLIP BEHAVIOR IN RC BEAMS BASED ON OPENSEES

粘结滑移性能的数值分析是钢筋混凝土结构研究的热点,该文在总结现有粘结滑移本构关系的基础上,采用分离式思想在OpenSees中建立粘结滑移精细化分析模型,并通过拉拔试件与RC梁构件的数值分析研究梁中钢筋与混凝土的粘结滑移作用,同时考虑箍筋量对构件滑移分布的影响。经过该文分析可知,该数值分析模型具有一定的合理性,能较准确的反映出粘结应力、滑移等分布的规律;通过梁构件数值分析可知,其整体性能受到粘结性能、钢筋滑移量大小及箍筋配置等的影响,箍筋的配置对构件局部滑移会产生一定的影响,但对滑移的整体分布影响并不显著。Many scholars have done a lot of research on bond-slip behavior in reinforced concrete structures. Besides experiments, numerical analysis is also important. In this paper, on the basis of summarizing bond-slip models nowadays, a refined model in OpenSees according to the method of discrete model is built and then the bond-slip behavior between rebar and concrete is studied through analyzing a pull-out specimen and RC beam component. The influence of stirrup on bond stress and slip distribution is considered. From the analytical results, it is found that the numerical model is reasonable to reflect the bond stress and its change law. At the same time the phenomena of beam simulation show that many factors have effects on its whole performance such as the bond stress, slip of rebar and ratio of stirrups which can affect the bond-slip distribution. The stirrups affect the slip in part of the beam but in general it has little effect.国家自然科学基金项目（51261120376,91315301-12

ELASTOPLASTIC NUMERICAL SUBSTRUCTURE METHOD OF REINFORCED CONCRETE FRAME STRUCTURES

大型复杂土木工程结构在地震作用下失效破坏可能由部分关键构件严重损伤破坏导致,而大部分构件仍处于弹性或小变形状态。该类结构的地震损伤和破坏全过程分析涉及超大规模系统强非线性动力分析,目前尚缺乏能很好兼顾效率和精度的计算理论,基于此,该文提出一种新型高效且实用的弹塑性数值子结构理论和计算方法,将大型复杂结构系统的大规模非线性计算问题转化为整体结构适度规模的线弹性分析和数量与规模均较小的局部隔离子结构非线性分析,其中,线弹性整体结构刚度矩阵的集成及LU三角分解仅需进行一次,大大提高计算效率;少数屈服构件的子结构非线性分析采用精细化有限元模型或不同类型单元模型,精确模拟构件局部损伤破坏机理,有效提高结构整体的计算精度。最后通过对一榀平面钢筋混凝土框架结构进行地震动力弹塑性数值子结构方法分析,验证其高效性与精确性。During the seismic process of earthquakes, larger-scale civil engineering structures might fail due to the serious damage to some key structural members, whereas most structural components might remain elastic and experience small deformation. It is a challenging task to simulate the behavior of such structural systems due to the trade-off between computational efficiency and numerical accuracy. This paper presents an efficient and practical elastoplastic numerical substructure method, in which the whole structural seismic analysis is divided into linear elastic analysis of a master structure and nonlinear analysis of limited numbers of small-scale substructures, to balance the computational efficiency and numerical accuracy. During the linear elastic analysis of the master structure, the formation and LU triangular decomposition need to be done only once as the equivalent stiffness matrix remains constant, resulting in high computational efficiency of the master structure. Rational or refined models can be used in substructure systems to model the local damage mechanism, improving the numerical accuracy of the whole structure. Seismic analysis of a reinforced concrete frame structure is performed to verify the novel numerical substructure method.国家自然科学基金项目(51261120376;91315301-12

考虑P-⊿效应的框架结构弹塑性数值子结构分析

几何非线性是土木工程结构在强震作用下动力时程分析过程中必要的考虑因素。该文基于数值子结构方法,结合平面Euler-Bernoulli梁柱单元的几何大变形理论,将平面框架结构的非线性分析转化为线弹性主结构的弹性分析,并提出材料和几何非线性修正力项,作为等效为外荷载项施加于主结构以考虑结构的双非线性。最后,对一平面钢框架结构进行地震动力时程分析,分析结果表明考虑了双非线性的数值子结构方法具有良好的精确性与高效性;同时,几何非线性对结构动力响应具有重要影响。国家自然科学基金项目(51261120376;91315301-12

REFINED ASEISMIC ANALYSIS OF LOW-DUCTILITY RC FRAME BUILDING BASED ON NUMERICAL SUBSTRUCTURE METHOD

该文以钢筋混凝土低延性框架结构为分析对象,总结该类结构及相关构件数值分析研究现状;基于桁架模型研究柱及节点组合体等关键构件的精细模型化思路与方法,并分别采用试验予以验证;以此为基础,借助在Open Sees软件中开发的数值子结构方法及平台,以汶川地震中严重受损的多层钢筋混凝土框架结构为对象建立精细化数值子结构模型,通过局部构件的精细分析研究其在强震作用下的抗震性能及失效模式。经该文研究表明采用桁架模型建立易于发生脆性破坏的柱及节点组合体等关键构件的精细化模型合理且准确;选择数值稳定且更适用的精细化模型与数值子结构平台分析涉及不同类型且易发生脆性破坏的低延性结构更具优势;针对低延性框架,不宜采用位移角限值作为结构性能评估的唯一判断依据,在分析中需考虑未达到目标位移前结构可能发生的脆性破坏模式。This paper firstly provides a short summary on the current research status on the numerical studying of low-ductility reinforced concrete （RC） frames and their related components, such as columns and joint subassemblages. Then detailed numerical modeling approaches of these key components using a truss model are provided and evaluated using several experiments. Finally, a numerical substructure method （NSM） developed in OpenSees is employed to build the detailed substructure model for analyzing a damaged RC frame subjected to Wenchuan Earthquake, and its aseismic performance and failure mode are studied in a detailed way according to the local performance. This study indicates that： the truss model performs well in simulating the nonlinear behaviors of columns and joints, especially to predict the brittle failures; numerical substructure method has great advantages, such as good numerical stability and applicable refined models, to study the performance of low-ductility RC structures; from the analytical results ofdarnaged RC frame, it can be found that displacement or inter-story drift should not be the only criterion to evaluate the low-ductility structures, and instead the possible brittle failures must be considered in the aseismic analysis.国家自然科学基金项目（51261120376,91315301-12

Numerical substructure method for structural nonlinear analysis

结合震害调研及数值分析可知,结构最终失效可能仅由部分关键构件破坏引起,大部分构件仍处于弹性或小变形状态。因此为提高计算效率,在结构全过程分析中一致采用非线性单元建模并非必要,同时为准确考虑关键构件的非线性响应,本文提出一种新的数值子结构建模策略。进入弹塑性状态后,针对一般钢构件或钢筋混凝土构件采用动态替换子结构方法在单元或截面层次将其替换成非线性单元或非线性截面,并基于OPEnSEES平台开发了两类新单元予以实现;针对可能发生严重损伤的关键构件,采用隔离子结构方法将其隔离并建立精细化分析模型,考虑主、子结构间不同尺度边界耦合,并推导了切线刚度的传递关系,采用ClIEnT/SErVEr技术在OPEnSEES平台开发了一类新的接口单元予以实现主、子结构之间的信息传递。为验证新开发单元的合理性,分别以钢及钢筋混凝土平面框架结构为例,采用纤维单元、动态替换子结构方法以及隔离子结构方法建模进行静、动力分析。计算结果表明,采用本文提出的动态替换子结构方法与常规建模方法的计算结果完全吻合并且可大幅缩短计算耗时,随着荷载水平的增大,结构中受到动态替换的构件比例急剧增大,计算效率提高程度略有降低,但仍远高于常规模型;采用本文提出的接口单元可准确传递主、子结构间的界面信息,为隔离数值子结构方法在结构弹塑性分析中的应用提供了基础。According to seismic damage analysis of structures,the whole structure might fail due to the serious damages of some key structural members.In spite of this,it was observed that most structural members might keep elastic and experience small deformation during the process.Thus it is unnecessary to use nonlinear models for the whole structures during the entire process of seismic analysis.A novel modeling methodology,named numerical substructure method,was presented considering the demands of computational efficiency and accuracy,including dynamic replacement substructure method and isolation substructure method.In the first method,once the elastic structural members(e.g.steel members and reinforced concrete members)yielded,they were replaced in the element and section levels by nonlinear models.In the isolation substructure method,the key members were isolated from the master structure,and refined FE models for the members were built in other platforms.The data transfer(e.g.displacement,force and tangent stiffness)between master structure and substructure was achieved by using CS technique.The above numerical substructure methods were implemented into a general finite element framework,OpenSees.To verify the newly developed numerical substructure method,two steel frames and a RC frame subjected to both static and dynamic loading conditions were taken as application examples.The analysis results using dynamic replacement elements model agree well with that using normal fiber elements model,while the computational time greatly reduced,although this advantages become less remarkable with increasing number of members yielded and replaced;the data transfer between master structure and substructures are efficient and accurate,enabling isolation substructure method to be potentially used in large scale structural elastic-plastic analysis.国家自然科学基金(51261120376;91315301-12)资助项