The Effect of Slabs on the Failure Mode of Reinforced Concrete Frame Structures

A majority of reinforced concrete frame structure failure patterns resulting from the May 12, 2008 earthquake in Wenchuan County, P. R. China were analyzed. It was found that the main failure mode of frame works was “strong beam, weak column”, which conflicts with the design criteria of “strong column, weak beam”. The cause of this failure pattern was analyzed. A new concept is put forward that should be considered in design work. The over strength caused by slabs connected monolithically to the beams is analyzed. The joint types, transverse beam stiffness and lateral drift influence the reinforcing effect of the sla, Moreover, a reinforced concrete frame model was simulated using the program ABAQUS. The slab reinforcement stress distributions at different lateral drifts were analyzed and the effective flange width value proposed.     

Experiment and FEM Analysis on the Joint of Inserted Steel Beam

A new composite structure which is composed of steel beam and concrete girder is introduced in fuel electric plant construction. With different height of concrete girders with or without anchor bar, two scale models from an actual project were designed and tested. It is shown that the maximum restraining moment of ends of steel beams is approximately 60kN*m; influence of anchor bar is little; the one with 600mm high concrete beam is damaged by shear, and the others steel beam is damaged by bending failure. Finite element models were built for supplementary analysis, and the result indicates that critical value of the height of concrete beam of different failure modes is 700mm; stiffness of shear key and thickness of floor have great influence on the structure; size of anchor bar has little influence; and width of the end of the steel beam has certain influence.     

Discussion on Negative Flexural Strength of Beams Including Slabs

In this paper, the provisions in different design codes and some tests on the identification of the negative strength of beams including slab-bars are compared and analyzed. The results of analysis demonstrate that the effective width of slabs is a converted width for calculation. It isn't the actual working width of the slab or the yield slab width. According to the maximum storey drift, the frames can reach, an effective width of slabs can be defined as six times the slab-thickness width on each side of the web. Considering the participation of reinforcement in slab into resistance of the beam against negative flexure, the anchorage of tension bars and the transverse reinforcement placement in slab should be taken into account to ensure the effective work of longitudinal slab bars.     

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.     

Analysis of Failure Mechanism of RC Structures with Specially Shaped Columns Affected by the Diaphragm

With the flexibility-based fiber model,the seismic behaviors of RC structures with specially shaped columns,designed according to the current code,are analyzed under unidirectional rare earthquakes using nonlinear dynamic analysis method.The beam strength is calculated with or without consideration of the diaphragm and its reinforcement.The results are compared and the conclusion has been drawn that the bending capacity of beams would be increased due to the effect of diaphragm and its reinforcement,and which would change the failure mechanism of RC frames under rare earthquake,especially in high intensity areas.Therefore the influence of the diaphragm should be considered during the seismic design of the type of structure.     

Mechanical Characteristics of Earthquake-Resistant Reinforced Concrete Frame Joints

On the basis of analysis and induction of experimental results on earthquake-resistant frame joint both at home and abroad, it is clearly pointed out that the mechanical characteristics of the joint in which shear failure may occur after yielding of longitudinal rebars at the beam end or at the column end are classified into three types, i. e ., diagonal tension, diagonal compression and a combination of diagonal tension and diagonal compression. A region of these three types of mechanical characteristics in the coordinates composed of relative shear force and relative ratio of transverse reinforcement is given, and the variation law and the corresponding reasons for the mechanical behaviors with the relative transverse reinforcement are analysed.     

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.     

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.     

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.     

Effects of Infill Walls in Frame Structures under Frequent Earthquake:Revelation from Wenchuan Earthquake

Based on a three-story RC frame, the analysis of the structure with various layouts of infill walls under frequent earthquake was conducted. The results indicate that when the infill walls and their different layouts are incorporated into the structural model, the seismic performance, such as dynamic properties, characteristics of regularity, and internal force distributions would change significantly. It should be also mentioned that because of the constraint of infill walls, the sum of moments at column ends is much larger than that at beam ends at the frame column-beam joints. It is suggested that infill walls should be adequately considered in the mechanical models during seismic analysis.     

Experimental Analysis of Pre-cracked RC Beams Strengthened with EB-FRP and HB-FRP

On the basis of the crack characteristics of aging RC beam bridges, the cross-section of RC simple beams with different pre-cracking levels were strengthened by the externally bonded FRP（EB-FRP）and the FRP-bolt hybrid bonding（HB-FRP）respectively to check the strengthening characteristics of HB-FRP. The flexural test with symmetrical loading on two points was conducted to study the mechanical behavior and failure mode of pre-crack beams strengthened with EB-FRP and HB-FRP. The influence of pre-cracking level on the FRP initial debonding load and FRP utilization ratio was assessed respectively. The test results show that the flexural capacity of pre-cracking beam strengthened with HB-FRP can be improved by 30%~44% compared with the one with EB-FRP. The failure mode has been changed from FRP brittleness debonding of beam strengthened with EB-FRP to obvious ductility failure of beam strengthened with HB-FRP. Furthermore, the crack distribution of RC beam has obvious influence on the FRP initial debonding load, the FRP utilization ratio and the failure mode of strengthened pre-crack beams.     

Lateral Bearing Capacity and Simplified Equations of Dry Stack In filled Reinforcement Concrete Frame Structure

The mechanism and lateral bearing capacity of reinforcement concrete (RC) frame with dry stack in filled panel (DSIP) were investigated using quasi static experiments and finite element models. According to the parallel model and equivalent strut model, the lateral bearing capacity of RC frame and DSIP were researched separately. Results show that: 1) The plain stress element and interface element are applicable in finite element (FE) model analysis. According to the FE model, the failure of RC frame with DSIP is caused by the damage of frame; 2) Lateral bearing capacity of DSIP is mainly from the friction between bricks in the panel, which can be divided into 3 stages: constant stage, increasing stage and ultimate stage; 3) Equations for lateral bearing capacity of DSIP were proposed and verified by FE model results.     

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.     

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.     

Several Matters to be Noticed During the Moment Modulation Design of Prestressed Concrete Frame

The moment modulation of prestressed concrete frame has some differences compared with that of continuous beam.Based on the analysis of ratio of column linear rigidity to beam one,form of load,second moment and plastic hinge in column,this paper is intended to get some helpful advise for moment modulation design.     

Experimental Analysis on Shear Strengthening Capacity of Secondary Dapped end Beams

Because section steel can only be extended to the edge of the support, when a simple support RC beam is reinforced by bonded section steel, a notch comes into being at the end of the beam which is called a secondary dapped end beam, making the stress state of the beam more complex. Through experimental analysis on 21 dapped end beam specimens shear reinforced by steel plate bonded, the deformation process, performing characteristics and failure mechanism of the specimens were investigated. The result shows that two steel bonded forms, including horizontal steel plate and oblique steel plate with angle 45° bonded, delay the appearance of cracks significantly and improve the maximum bearing capacity by 102% and 93%. Due to the impact of stress concentration at the notch, the main modes of damage include concrete tensile or shear failure with the result of bonding failure of a steel plate. By changing the width of steel plates and analyzing different reinforcement effects, formula of bearing capacity of shear reinforcement was proposed based on the method of truss analogue, which provides a reference for engineering application.     

Experimental Research on Steel Tube Confined Concrete Column Ring Beam Joint with Shear Ring under Direct Shear

In this paper,through direct shear tests on 3 steel tube confined concrete column ring beam joints with shear ring,the ultimate capacity,the mechanical mechanism,the sliding of ring beam relative to steel tube and the ultimate failure mode of ring beam were analyzed.The results showed that the ultimate failure mode and the calculation of capacity of ring beam joint awaited further tests and analysis.     

A Group Quantitative Method for Adjusting the stock structure of Products

Products in enterprises are various in specifications. In order to get better benefits, it is essential for the managers of these enterprises to make right decisions for adjusting the stock structure of products. This paper develops a new modil system, which includes a series of interactive models, such as quatitative analysis, balance and evaluation models etc, and provides a frame for using these models to support the decision-making of product structure adjust.     

Experimental Investigation of Steel Frames with Infill Prefabricated Reinforce-Concrete Shear Walls

In order to improve seismic performance of steel frame with prefabricated reinforce-concrete infill shear walls (SFCW), the ear bar device was used in the connection between the steel frame and the infill wall. Two one-bay, two story and one-third scaled models of SFCW were tested with low cyclic load. The working performance of ear bar connection, the cracks development in infill walls and deformation performance of SFCW were investigated. And the failure mode, hysteretic behavior,stiffness degradation,deformation and ductility and energy dissipation of composite structure were analyzed. The comparison study of steel frame with prefabricated, cast-in-place and silt reinforce-concrete infill shear walls was carried out. The results show that no failure occurs in the connection between the steel frame and the infill wall because ear plates below and up the beam-to-column connections are added in the specimens, and the connection device of ear plate presents good working performance. The properly designed SFCW has good ductility.     

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.