TENTATIVE INVESTIGATION OF THE BEHAVIOR OF REINFORCED CONCRETE FRAME CORNER JOINTS UNDER LOW CYCLE LOADING

In this pager, four full-scale corner joint assemblies of reinforced concrete frame beam and column with different detail structure are tested under low cycle loading, The process of damage development and the characteristics of break of the assemblies in the course of alternately increasing positive and negative bending deformation are learned Strength, stiffness and ductility of assemblies and the various regulations of energy consumption are also studied. Compared with these properties, the anti-seismic behavior is tentatively commented. Besides, the test results of the strain distribution of beam and column longitudinal bars and stress state of joint stirrups are analyzed.     

THE DETERMINATION OF A CRACK IN STEEL FIBRE REINFORCED LIME-SAND CONCRETE

This paper studies the determination of a crack in steel fibre reinforced lime-sand concrete and its precision by acoustic emission(AE).The main AE paramters which influencethe precision of the determination of a crack are introduced,The properties of the lime-sand concretecan be increasted greatly with the steel fibre,The result in this paper can be used in the study of fi-bre re inforced cement concrete.     

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.     

RESEARCH ON THE SECTION GEOMETRY RELATIONSHIP OF REINFORCED CONCRETE SLENDER MEMBER

By using Hellinger-Reissner's calculus of variations,this paper presents the usual method with which the section strain distribution state of reinforced concrete member can be derived from the basic balance equation.This method is suitable for any difinite form of strain distribution of the compressional zone of concrete.It is made clear by calculation that if the compression zone of concrete has linear strain distribution in the deformation process,the strain of tension bar and the distribution mentioned above can satisfy the assumption of plane section multaneously.     

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.     

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.     

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.     

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.     

Study on the Seebeck Effect in Steel-slag Concrete

The Seebeck effect of steel slag reinforced concrete was studied in this paper.The effect of steel slag content and curing period on Seebeck effect were focused on especially.The experimental results show that Seebeck effect of steel slag reinforced concrete was discovered,and a good linear relationship was observed between thermoelectric force(TEP)and temperature differential on the specimen;The linear relationship was from enhancing to weakening with increasing steel slag content;As the curing period extends,the Seebeck effect of steel slag reinforced concrete was better,and TEP became steady.     

A PRACTICAL METHOD FOR SELECTING STEEL USING COMPUTER AIDED DESIGN(CAD)SYSTEM FOR REINFORCED CONCRETE FRAME

How to select automatically the disposition of steel bar in a computer aided design(CAD)system for reinforced concrete frame structure is aproblem relatedt ot he practicality and increasing capacity of the CAD system.This paper suggests a practical method for selecting steel bar of beam in framestructure with the application of knowledge and experience of the experts forreasoning and judging.The method is convenient for calculation.The results ofcalculation are in agreement with detailing requirement and usual engineeringpractice.The method has great practical value.     

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,     

Research on Deformation Equation and Dynamic Properties of Hybrid Structure

Based on the principle of interactive analysis,the deformation equation of hybrid structure which contains rigid character value is established using the analysis of the frame - shear wall structure for reference, considering the rigid zone between concrete beam and concrete - tube, the shear deformation of concrete - tube, axial deformation of steel frames and semi - rigid connection between steel columns and concrete beams. Assuming the hybrid structure to be a continuous elastic structure with infinite degree of freedom, a free vibration equation has been built and the formula for calculating free vibration period has been deduced. The influences of various parameters to the coefficient of free vibration period relating to rigid character value are discussed according to some diagrams. It is shown that the rigid zone can lessen the free vibration period but the shear deformation of concrete - tube, axial deformation of steel frames, and the semi -rigid connection between steel columns and concrete beams can enhance the free vibration period.     

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。     

EXPERIMENTAL RESEARCH OF THE MOMENT MODULATION INFLUENCE ON CRACKING AND DEFLECTION OF CONTINUOUS REINFORCED CONCRETE BEAMS UNDER SERVICE LOADS

Through the static tests of five two-span continuous beams with a relatively small steel ratio, the regularity of redistribution of internal forces of continuous beams with moment modulation is studied, and the moment modulation influence on cracking and deflection of continuous reinforced concrete beams under service loads is analyzed in detail. The conclusions obtained may be used as reference materials for drafting of design code considering redistribution of internal forces.     

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 Research on the Seismic Behavior of the Interior Joint with High Shear - Compression Ratios in the Frame

The reversed cyclic loading tests of 5 nearly full-scale beam-column assembly specimens with high shear-compression ratio under different axial loads in reinforced concrete plane frames have been completed,which cover the shortage in the field of high shear-compression parameter among seismic joint experiments in the world.Based on relatively complete measuring and analyses of the law for the bond and slip of the beam bar through the joint,the stress of the level stirrup legs and hysteretic dissipated energy and the change of rigidity,the characteristic of shear transfer mechanisms and damage development and comprehensive seismic behavior of the assembly are proposed in this paper.It makes it possible to improve design codes and to establish relatively reasonable analytic modes and hysteretic modes in inelastic dynamic response analyses of the frame.     

INFLUENCE OF PLASMA TREATMENT ON SURFACE ENERGY OF UHMW-PE FIBRES

The fibre-resin adhesion has been reinforced by plasmatreatment on ultra-high molecular weight polythlene(UHMW-PE)fibres.This paper reports a study of the mechanism of the adhesion from thechanging of the surface energy.The experimental results show the surfaceenergy of the fibres has been greatly increased for plasma treatment andthus meets the prerequisite of fibre-resin adhesion.The fibres are comple-tely rinsed in the epoxy matrix.     

Experimental analysis of strengthening effect of corroded reinforced concrete beams strengthened with bolted steel plates

In order to study the mechanical behavior of corroded reinforced concrete beams strengthened with bolted steel plates, this paper designed 12 reinforced concrete beams. These beams were corroded by using accelerated electrochemical corrosion method with a designed corrosion ratio of 10%. The pre-compression experiments were performed for all RC beams before strengthening and the maximum crack width was controlled as 0.2 mm. According to the thickness of concrete cover, the beams were divided into 3 groups. Each group was composed of one comparative beam and three tested beams strengthened by steel plates bolted with study according to the thickness of steel plates which were 3 mm, 4 mm and 5 mm, respectively. It was shown that the strain distributions along the height of the strengthened beams at middle-span were in good agreement with the plain section assumption basically. The serviceability performances of corroded RC beams were significantly improved and these ultimate bearing capacities increased obviously. The steel plate bolted with stud effectively reduced the crack width and the extension height of reinforced concrete beams. It was indicated that an increase of steel plates with 35 mm resulted in a decrease of deflection by 13%51% when beams had the same thickness of concrete cover and corrosion ratio. Influence of the thickness of concrete cover on the ultimate bearing capacity was not obvious.     

Composite Steel- concrete Frame Beam with Reinforced Negative Bending Regions

Considering the large negative bending moment at the end of frame beam and low tensile strength of concrete,a new composite steel-concrete frame beam(CSCFB),reinforced by a T shape steel beam at the negative bending regions,was brought forward.Through two full-scale of single-layer CSCFB frame models experiment,the load-displacement curves of CSCFB and strain distribution at cross section were obtained.Compared with the ordinary composite beam,the T shape reinforcing section can enhance the beam stiffness effectively,and make it distribute reasonably.The segment flexural rigidity method is presented and validated.     

Partial Pressure Problem About Continuous Rigid Frame Bridge Anchorage Zone of Thin Concrete Box Girder Webs Carrying Large Tonnage

With continuous rigid frame bridge span increasing,cantilever construction of large tonnage anchor are also becoming more common,but local stress distribution is complicated on prestressed anchorage zone of thin concrete box girder webs by the large tonnage,which reveals its distribution of post-tensioned concrete bridge structure to be solved in the future.Based on the theory,some key points such as pressure factors,destruction and the reasons for the compression type crack were discussed in the paper.By using the North Approach continuous rigid frame concrete bridge of Yangtze River Bridge project example,the local compression strength,crack resistance and the smallest protective layer thickness of the first segment of one continuous rigid frame box girder bridge under design value Rally 4882.5 kN of No.T2 tendom,according to the local pressure formulas of Code for Design of Highway Reinforced Concrete and Pre-stressed Concrete Bridges and Culverts of China(JTG D62-2004) and Finite Element Method,were checking.Both the results verify that meets the standard requirements.The results reveal that the design of a web-Laced with horizontal steel mesh sealed off side stirrup can solve the partial pressure problem.