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.     

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。     

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.     

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.     

Spatial Calculation Methods of Three Main Trusses Continuous Plate truss Composite Bridge

According to the structural features of three main trusses continuous plate truss composite bridge, two composite beam methods are presented by constructing the displacement mode of composite beam elements and deriving the stiffness matrix of composite beam elements. The characteristic of composite beam method one is that the bridge slab is taken as the top flange of the chord of main truss and combined with the chord of main truss to form a steel concrete composite beam; the characteristic of composite beam method two is that the bridge slab is taken as the top flange of longitudinal and traverse beam and form a steel concrete composite beam with longitudinal and traverse beams. And as for the conventional plate beam composite method, the slab is characterized by forming bridge slab system with continuous isotropic sheets and longitudinal and traverse beams to bear load. Also, the comparison between theoretical results and experimental ones verifies the effectiveness of the above three methods.     

FEM Dynamical Analysis of the Reinforced Concrete Beam with Bonding Steel Plate

In order to researchmechanical capability of the reinforced concrete beam with bonding steel plate, adopting separatemethod to establish finite element model of the reinforced concrete beam with bonding steel plate, using FEM to study dynamical characteristics of the model, have got good results which can not be easily got using traditional resolution method, which can give referenceto study dynamical characteristics of the reinforced concrete beam with bonding steel plate.     

Interaction Working Behavior About the Internal and External Wall of Foam in place Cavity Wall

In order to study the stability of foam in place cavity wall, the capacity of reinforced concrete strip ear and tie involving in cavity wall deformation, the broken shapes and mechanical performance of the cavity wall, the effective measures was seaked to improve deformation capacity and overall performance of the cavity wall.13 patches of cavity wall and 1 patch of solid wall were built and seismic tests of which were carried out.The lnfluence of some constructional measures on mechanical behavior and deformation properties of the wall and vertical pressure and insulation layer thickness on the relative displacement difference of the internal and external wall of foam in place cavity wall was analyzed.Finally, the capability of reinforced concrete strip ear and tie working interactively between the internal and external wall of foam in place cavity wall was analyzed.It is found that deformation capacity of the cavity wall is improved efficiently with constructional column and the high bonding strength, shearing strength and pressure strength of foam in place insulating mortar have certainly a positive influence on the bearing capacity of the wall.The reinforced concrete strip ears play the leading role in reinforcing connection of the internal and external wall of foam in place cavity wall and guaranteeing out plane stability of the external wall.When walls crack seriously, the ties can play an important role in supporting and drawing the wall and preventing wall collapse.Furthermore, the reinforced concrete strip ears and ties which are the main construction measures to coordinate the internal and external wall work together perform a great variety of tasks.Therefore, the reinforced concrete strip ears and ties should be designed rationally to guarantee playing their respective roles.     

新型组合梁板连接中板的抗弯性能

在高层建筑结构设计中，由于上部荷载较大或梁的跨度较大，使得梁的截面高度较高，通常会影响建筑的有效层高和建筑的总体高度。为了减小各层梁板结构高度，有效增大各层净高，提出了一种钢箱梁嵌入现浇板的新型组合梁板连接方式。针对这种新型连接方式，对6个钢箱梁混凝土板组合连接区域进行了板承受支座负弯矩的单调加载试验，对比分析了采用钢箱梁嵌入混凝土板组合楼盖与传统栓钉连接组合楼盖中板抵抗支座负弯矩的性能差异；并利用ABAQUS对试件进行了有限元分析。试验与有限元分析结果表明：采用钢箱梁嵌入板连接组合方式，其混凝土板抵抗支座负弯矩的能力与传统连接方式板抵抗支座负弯矩能力没有明显差异。     

An improved method for and error evaluation of modal pushover analysis

Based on evaluation of the basic principle and error of the modal pushover analysis method, an improved method is suggested by selecting rational values of stiffness reduction parameters of beams and columns in a reinforced concrete frame corresponding to the global target displacement ductility ratio. A 10 story and a 16 story reinforced concrete plane frame are designed as examples to investigate the influence of higher modes. Nonlinear seismic responses of the two frames under excitations of seven earthquake waves of varying earthquake intensities are selected to be the reference points for a comparison study. The changing rules of the results of modal pushover analysis and modified modal pushover analysis with respect to various natural fundamental periods and different earthquake intensities are studied. Research results show that the error of modal pushover analysis and modified modal pushover analysis will not increase with a larger fundamental period, which implies that modal pushover analysis can cover the effect of higher modes reasonably. When the degree of nonlinearity of the structure is more severe, the modified modal pushover analysis we suggest could decrease the error of normal modal pushover analysis to a certain extent.     

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.     

Impact of Temperature in Air-conditioned Room on Blood Rheological Characteristics

Based on the reversed cyclic loading tests of 21 nearly full-size interior joints in completed reinforced concrete frames,the law of bond deterioration of beam bars crossing the joint is tested and analyzed,which is influenced by the axial load ratio,shear-compression ratio,reinforced bar strength,concrete strength and the relative length of beam bars crossing the joint. By the nonlinear fitting method, the formula of the bond stress r between steel crossing interior joints and concrete under different loading step is obtained. According to the loading approach, the propositional formula of the relative length of beam bars crossing the joint hc/d is presented, which is influenced by axial load ratio, shear-compression ratio ,reinforced bar strength and concrete strength.     

内框架箱型混凝土结构施工活荷载实测分析

施工期早龄期钢筋混凝土结构与模板支撑系统组成临时承载体系为时变结构,其承担的荷载主要有新浇筑混凝土自重与包括施工人员和设备荷载以及混凝土浇筑时产生的冲击和振捣荷载在内的施工活荷载。将多层连续施工时变结构体系模拟成一组弹性支撑连续板,根据该模型分析了施工期现浇钢筋混凝土结构的受力特性。根据现场实测数据,以构件有效承载面积为统计对象,计算了混凝土施工荷载的统计参量,并参考相关研究成果,以95%的置信度对施工期活荷载标准值进行反演,建议施工活荷载标准值取2.5 kN/m 2。     

Low-cyclic Fatigue Behavior of Reinforced Concrete Column Subjected to Symmetric Displacement Cycling

Under seismic action, the damage of critical regions in ductile reinforced concrete structures can be regarded as combined results of cumulative damage caused by positive/ negative displacements with different displacement levels after yielding. On the basis of symmetric low-cyclic fatigue experiments on eight half-scale RC columns under different displacement levels, the development of cumulative damage and relationships between low-cyclic fatigue life and symmetric displacement amplitude are investigated. It is hoped that on this ground, more rational damage criteria for RC structures can be put forward.     

Nonlinear Stiffness Matrices of Plane Beam Element Including Initial Stress and Strain Item

There were often happened cases for beam elements with initial stress or initial strain while the geometrically nonlinear analysis was performed for the plane structure. The deduction of stiffness matrices was awfully difficult because the nonlinear stiffness matrices included node displacement vectors and extensive matrix operations. Based on the nonlinear geometric equation of plane beam element and general elastic relationship of stress-strain including initial stress and initial strain,the tangent stiffness matrix was derived. All explicit formula of stiffness matrices including initial stress and strain item have been developed by use of the MATLAB Mathematical Tools. The results are of great significance to the nonlinear finite element programming for plane beam elements.     

基于内聚力模型的锈蚀砼梁抗弯刚度

粘结性能退化是导致锈蚀钢筋混凝土构件力学性能下降的主要因素之一，基于锈蚀构件粘结性能实验研究成果与内聚力模型，建立了有厚度的双线性内聚力单元与分离式钢筋混凝土梁分析模型，引入粘结界面层，研究了粘结性能退化对锈蚀钢筋混凝土梁抗弯刚度的影响。结果表明，双线性内聚力单元可以有效模拟钢筋与混凝土之间的粘结机制，而根据锈蚀深度确定的有厚度的粘结单元能合理描述锈蚀程度对粘结性能的影响。数值分析结果与实验及经验公式对比，表明了文中方法的有效性和合理性。     

Test Analysis on Prestressed Frames with Three Kinds of Beam-column Section Strength

"Strong column with weak beam","strong beam with weak column" and"column & beam with equal strength"can be existed in one-storey prestressed concrete frames and the top storey of mult-storey prestressed concrete frames.Through the test of four prestressed concrete frames under vertical load,three kinds of prestressed concrete frames performances are studied,such as ultimate load,deflection,displacement ductility,redistribution of internal force.When the relative height of equivalent compression zone is smaller enough,the test proves that three kinds of prestressed concrete frames can realize full redistribution of internal force and have better displacement ductility,the width of cracks and deflections can satisfy the rules of code for design of concrete structures.     

塑性铰区采用FRC柱试验研究及正截面承载力分析

采用简化的纤维增强混凝土应力应变关系,根据截面变形的平截面假定和截面力的平衡方程,推导出塑性铰区采用纤维增强混凝土柱在不同极限状态时的曲率。根据各极限状态点曲率,求得截面上各分布力,对截面形心轴取距,到塑性铰区采用FRC柱的开裂、屈服、峰值和极限点的弯矩表达式。与试验结果对比表明,计算值与试验值吻合较好。     

Simulation Analysis of Flexural Performance of Reinforced Concrete Beam in Salt-frost Environment

Considering the damage of concrete mechanical properties and bonding behavior between the steel bar and concrete after the freezing and thawing function in the numerical simulation, the nonlinear analysis on flexural performance of reinforced concrete beam which experiences different salt-frost cycles is conducted, and the evolution law of resistance performance of reinforced concrete beam is studied. It is shown that, in the salt-frost environment, the decrease of concrete mechanical properties is the main reason that causes the degeneration of RC beam on flexural performance, while the reduction of bonding property has an unobvious effect on the beam resistance performance. When the salt-frost cycles reach a certain level, the beam failure pattern would change from the under-reinforced failure to over-reinforced failure. The freeze-thaw damage of bonding property in the beam-ends anchorage zone has a certain effect on the beam resistance behavior, especially for the more serious freeze-thaw degree, the resistance performance of the beam reduces about 4% than the perfect anchor beam.     

Experimental Analysis for Steel Box Concrete Composite Beam of Arch Bridge

A new steel concrete composite structure was proposed which composed of steel box beam, PC beam and PBH Shear connection. Bend test was carried out for the performance study of deformation and stress. It was found that Material advantages of steel and concrete were fully used and crack of concrete and local instability of steel box were avoided. And the deformation between steel box and concrete can be smoothed with PBH shear connection. As the calculated values showed good agreements with the test results, the proposed formulas can be reliably applied to the practice analysis. With the different parameters analysis, mechanic performance of the composite was obtained.     

Seismic Load Tests on Reinforced Concrete Beam-Column Sandwich Joints with High Shear Stress

Seven reinforced concrete Beam-Column sandwich joint specimens were tested under cyclic load. The performances of these specimens consisting of loads resistance, deflection, ductility, displacement, energy dissipation could satisfy the requirement of structures for seismic design. The phenomena that concrete in joint region was crushed by axial load or eccentric load were never observed,and final failure for a multitude of specimens occurred by shear force. Though a few of performances such as beam bar anchorage capacity were not as well as those of traditional joints ,it is feasible for sandwich joints used while establishing structures.