A Comparative Evaluation of Model Pushover and the Influence of Higher Modes

Three reinforced concrete plane frames with total heights of 6, 10, and 16 stories, respectively were taken as examples. Nonlinear dynamic responses of three frames under excitations of seven earthquake waves with varying earthquake intensities were selected as the datum mark of a comparison study. The changing rules of the responses analyzed by four kinds of ordinary Pushover Analysis and Modal Pushover Analysis were studied by reviewing the inter story drift ratio and rotation at beam and column ends. Results show that the error of inter story drift ratio analyzed by Modal Pushover Analysis essentially is invariable when the total frame height increases, while the error of ordinary Pushover Analysis is added corresponding to a larger fundamental period. This indicates that Modal Pushover Analysis can cover the influence of higher modes more reasonably. When nonlinear responses of frames were more severe, the inter story drift ratio errors of Modal Pushover Analysis and ordinary Pushover Analysis also increase correspondingly. The errors of rotation at upper story beam ends and the majority of column ends analyzed by Modal Pushover Analysis are smaller than those of ordinary Pushover Analysis.     

Improved Modal Capacity Spectrum Method for Estimating Seismic Performance of Structures

Performance-based seismic design involves how to confirm inelastic displacement demand of structures under earthquake in concise and reasonable way. Two shortages need to improve in analyzing the elastic-plastic seismic responses of structures if the traditional capacity methods are employed. The shortages are the uncertainty of equivalent high damp of elastic-plastic structures and the limitation of the higher order vibration mode effect being not taken into account. To solve these problems, the authors propose the concept and analyzing process of improved capacity spectrum method based on modal pushover analysis and the elastic seismic responses spectrum modified by strength reduction coefficient and ductile coefficient. The example of analyzing the performance of frame structure is shown which may be a simple and effective method used in engineering. This method has application potential in Performance-based seismic design.     

A Model Analysis to Beam Bar Slippage of Seismic Structure Joints

Many experimental results indicates, beam bar slippage within joints is a frequent local nonlinear response of reinforced concrete structures under the rare earthquakes. For the sake of modeling and evaluating seismic behaviors of reinforced concrete structures entirely and rational, the model way of the quantity and hysteresis order of beam bar slippage within joints, which was found in the elasto plastic earthquake response of structures, is discussed thoroughly. And the personal characteristics of several structure analysis ways to model the beam bar slippage within joints are evaluated respectively. Based on the results already gotten, a hysteresis model of beam bar slippage within frame joints is advanced, and the relative issues are also discussed. The beam bar slippage model suggested is convenience to the elasto plastic dynamic response analysis of whole reinforced concrete structures.     

Effects of the Adaptable Distribution for Lateral Forces Considering modes Coupling on Structural Pushover Analysis

Two high and flexible RC frame structures are analyzed;the paper explains the rise in the structural damping ratio and the base mode's drifting,and the modes coupling is caused by the greatly rising damping ratio.The paper also proposes that the modes coupling need be considered in the pushover analysis of the high and flexible RC frame structures.A CQC adaptive distribution for lateral forces in considering the modes coupling at every load step is given,and is compared with the traditional SRSS one.Meanwhile,some practical engineering suggestions are given.     

the rationality of plane model simplifying three dimension frame in seismic response analysis

A finite element model based on the flexibility method and a fiber section model of nonlinear beam column elements was adopted within the OpenSees framework. A typical multistory reinforced concrete 3D frame designed in accordance with the Chinese building code and a representative plane frame parallel to the X axis were used as examples. The relationships of the responses obtained from the plane and 3D models were studied by comparing global and local seismic responses of the frame, and by taking the responses of the 3D model under unidirectional earthquake action as a medium for comparison. Because the results show the global responses of the plane model are similar to those of the 3D model, it is reasonable to replace the 3D model with the plane model when examining global seismic responses. The local responses are evidently different. For the plane model under unidirectional action, numerous plastic hinges develop at the beam ends. Many more plastic hinges at column ends exist than in beams for the 3D model under bi directional action. Column ductility demands obviously exceed those of beams. The frame tends to develop a column sway mechanism, implying that simplified plane analysis model significantly underestimates the seismic responses of the 3D frame column.     

Experimental Investigation of "Column with Weaker Beam" Frame and "Column with Equally Strong Beam" Frame

By the way of experiment and analysis of two "one story and one bay" reinforced concrete frames, namely a "beam with weaker column" frame and a "column with equally strong beam" frame, the features of internal force redistribution are investigated and an elementary comparison about bending moment redistribution of three kinds of frames namely the "column with weaker beam", "beam with weaker column" and "column with equally strong beam" is given. Through this comparison, the objective existence of such "three kinds of frame" is proven, the moment redistribution is different for each frame and for the moment modulation, the elastic moment diagram and the difference of the internal force redistribution in different frames should be considered together.     

Deformation Analysis of Thermo Elastic Plastic on ReinforcedConcrete Structure Subjected to Fire

To investigate the mechanical behavior of reinforced concrete structure subjected to fire, the incremental thermo elastic plastic creep constitutive equations of steel and concrete in consideration of temperature and creep deformation were obtained based on different yield rules and the elastic plastic theories. The nonlinear analysis for reinforced concrete simply supported slab was carried out with consideration the variation of the mechanical properties of steel and concrete with temperature. The effectiveness and applicability of the constitutive equations were verified with the test results from relevant literature. The nonlinear analysis was employed for one bay one storey reinforced concrete frame under fire and the variation of displacement at partial nodes was analysed. It was found that the reinforced concrete structure at a high temperature would have a significant deformation. And the displacement change curves of beam column joints of reinforced concrete frame were not monotonous trend and there were inflexion points. The vertical displacement values of beam column joints were less than those at midspan of cross beam.     

Seismic performance of first floor corner joints of high-rise reinforced concrete frame structure

Crushing risk of corner column will increase substantially due to first floor corner joint shear failure of high-rise reinforced concrete frame structure under bi-directional loading and high axial compressive load caused by earthquake action. Therefore,     

Modeling and Its Application of Reinforced Concrete Columns Considering Nonlinear Shear Effects

A fiber beam-column element in conjunction with zero-length elements attached to its ends was proposed to simulate the flexural and shear mechanism respectively. Based on the Limit State Material model and the Shear Limit Curve model provided by OpenSees, the nonlinear shear effect of reinforced concrete column and its coupling with the flexural effect were defined. The reliability of the proposed model was validated by means of comparisons with existing test results. Finally, a plane frame from in-situ pushover test was simulated. It is shown that the proposed method, by taking the nonlinear shear effect into account, produces satisfactory results for frame columns with shear strength and stiffness degradation, while the conventional fiber beam-column element can hardly simulate actual flexure-shear failure mechanism for columns characterized by insufficient transverse reinforcement. The proposed method is applicable for nonlinear analysis of reinforced concrete frame structures with shear deficiencies.     

Inelastic Seismic Response of Reinforced Concrete Frame Structures Reinforced with HRB500 Steel Bars

To achieve sustainable development of construction industry, the application of HRB500 reinforcement with high strength and high ductility in RC structures is being promoted in civil and structural engineering in China. But few studies focus on seismic behaviors of RC structures reinforced with HRB500 bars. In this analysis, three RC frame structures on the Zone of Fortification Intensity 8 (0.3g) in China reinforced with HRB500, HRB400 and HRB335 bars respectively, are designed confirming to the latest draft of the revising Code for the Design of Concrete Structures. Then inelastic seismic response analyses of the three frames with multiple inputs of ground motions are conducted. The seismic response rules and seismic performances of the RC frame reinforced with HRB500 bars are compared with those frames reinforced with HRB400 and HRB335 bars. The analytical results indicate that under ground motions in rare earthquake level, the maximum displacements of the frame reinforced with HRB500 bars are roughly the same as those of the frames reinforced with HRB400 and HRB335 bars, while the rotation ductility demand of elements in the former structure is smaller than those of elements in the latter structures. It is also found that the frame reinforced with HRB500 bars develops a plastic energy dissipation mechanism that is dominated by beam hinges under major earthquake, and the maximum inter storey drift of the frame can satisfy the requirement in the Code for the RC Frame Structures.     

体育馆大跨度预应力次梁楼盖竖向振动模态分析

以重庆市铜梁县新城核心区小学建设项目3^#楼（体育馆）工程为背景，对其大跨度预应力次梁楼盖竖向振动模态进行模拟分析，并与实测结果相比较，评价其控制竖向振动舒适度的效果。根据建模思路精确建立的该大跨楼盖有限元模型，其模态分析结果与模态实测结果接近，相对误差约为5%；模拟分析及工程实测结果表明，该大跨楼盖前三阶振型均以竖向振动为主，结构自振基频满足我国现行相关规范的要求，竖向振动舒适度符合标准；与无底板的大跨次梁楼盖相比，增加底板后，其增幅最小的一阶频率增长了19.9%，表明增加底板可有效地控制大跨度预应力次梁楼盖的竖向振动。     

Seismic Tests and Pushover Analysis of Spatial RC Frame-Shear Wall Structures

Pseudo-static tests of three one-storey spatial RC frame-shear wall structures with floor slabs were conducted to investigate their failure modes and hysteretic behaviors. The test results were compared with those of pushover analysis. It is shown that: 1) damage of the frame beams occurs later and is less than that of the shear wall and the frame columns; 2) damage of the floor slabs under lateral loading is significant in regions close to the shear wall, and tensile stresses of slabs' steel bars in these regions are much larger; 3) in comparison with the case that the floor slabs are neglected, the maximum lateral load that a frame-shear wall structure can bear is larger in the case that the floor slabs are taken into account, and the contribution ratio of the shear wall also increases; 4) shear forces carried by the frame columns with identical cross sections and reinforcement details but located at different positions are close to each other on the whole.     

Nonlinear Finite Element Analysis of Reinforced Concrete Transferring Joints with Inclined Columns

A nonlinear finite element analysis using ANSYS is applied to the vertical mechanical behaviors of three specimens of reinforced concrete transferring joints with inchned columns, which are used in high - rise buildings. A comparison is made between the analytical achievements and the test results, including the mechanical behaviors, load - transferring path and the failure modes, and a good agreement is obtained. The reliability of the software ANSYS in the nonlinear analysis of such reinforced concrete structures is verified and developed.     

改性竹筋混凝土受弯构件力学性能试验研究

针对竹筋混凝土结构存在的问题,提出了多种对竹筋的改性方法。在此基础上,对12根采用不同配筋和不同改性方法的受弯构件(11根竹筋混凝土梁和1根钢筋混凝土梁)进行了试验研究,分析了不同改性方法和不同配筋率竹筋混凝土受弯构件的力学性能、破坏形态及其影响因素。研究结果表明：竹筋能有效提高混凝土受弯构件的承载能力;经过适当方法改性后的竹筋能确保竹筋和混凝土之间的有效粘结,其正截面强度计算可以采用平截面假定;竹筋混凝土受弯构件的破坏均为脆性破坏,其破坏形态与其截面配筋率有关。     

BEHAVIOR OF THE REINFORCED CONCRETE FRAME CORNER JOINTS SUBJECTED TO CLOSING LOADS

In this paper, experimental results on the tests of 15 full-scale reinforces concrete frame corner joints subjected to closing loads arereported. The primary variables are the compressive strength of eoncrete, thesteel ratio and the ratius of main bar bend. In order to investigate the stressdistributiens of the concrete in the cores of the joints, a nonlinear finiteelement analysis of the frame corner jonts is carried out. Possible damage andfailure modes of the frame corner joints are discussed herein. Based on observedand computed results, the formulae in terms of the steel ratio and the ratius ofmain bar bend and the corresponding useful recommendations are made for thedesign of the frame corner joints.     

THE STUDY OF ANTI-SEISMIC BEHAVIOR OF THE TOP CORNER JOINTS OF REINFORCED CONCRETE FRAME WITH THE INCLUSION OF STEEL FIBRES

This paper first discusses the limited effect of steel fibre reinforcement on plain concrete and reinforced concrete. Then, making a comparison among the test results of three full-scale top corner joint assemblies of frame, in which only two of them are added with steel fibres in joint zone. The advantageous and disadvantageous influence in anti-seismic aspect is investigated after adding steel fibres in the joint zone. Finally, this paper gives an overall comment on the application future of using the steel fibres in every kinds of joint of anti-seismic reinforced concrete frame.     

A Study on the Effect of Horizontal Strengthened Story to Super High- rise Steel Braced Frame

The Effect of horizontal strengthened story to the seismic response of super high - rise steel braced frame is analyzed in this paper through the finite element software ANSYS. By comparison of six different schemes of a 32 - story building, further research is presented on the influence of the quantity of strengthened story to the lateral stiffness, the inner force of components under earthquake and the distribution of shear force among inner tube and outer frame. According to the study, the Wuhan International Securities Mansion, which is a super high -rise steel structure, is described as verification. The response of the building is analyzed in small earthquake. The study can serve as the references of super high - rise structure with horizontal strengthened story design.     

CALCULATING SYSTEM FOR SECOND-ORDER EFFECT IN THE COLUMNS OF REINFORCED CONCRETE FRAMES

This paper makes an analysis and comparison of the calculatingsystem for second-order effect in columns of reinforced concrete frames proposedby scholars at home and abroad,and the systems adopted by codes of manycountries.The focus is on explaining the conceptual error and deficiency in somemethods.After expounding the basic law of the second-order effect in framecolumns with different restraints,this paper suggests an improvement of thecalculating system for second-order effect in frame columns for China's DesignCode of Concrete Structures.     

Optimization of Energy Dissipation Braces in Frame Structures

In this paper, the complex method of the nonlinear programming is used to optimize the parameters of energy dissipation bracing in energy dissipation braced frame. This method is realized with computer program and proved to be efficient. A 6-story reinforced concrete frame is used as a demonstrative example.     

Analysis on the Force-Transferring Mechanism of the Earthquake-Resistant Reinforced Concrete Frame Joints

On the basis of a summary of achievements from a large quantity of experimental studies both at home and abroad, in combination with the authors'experience in the experimental works on the reinforced concrete frame joints, their force-transferring characteristics are fully studied. The important fact that there is also a confined mechanism besides the inclined compressive strut and the truss mechanisms,is clearly pointed out. The influences of the three mechanisms upon the mechanical behaviors of the joint core concrete, the transverse and the vertical reinforcements,as well as upon the failure characteristics of the joint are also explored. Mechanical behaviors of the inclined concrete compressive strut and the factors causing its failure are specially discussed. These analyses provide theoretical bases for establishing more rational earthquake-resistant design criterion for reinforced concrete frame joints.