A Study on the Test Method for Post-tensioned Prestressed Concrete Frame

A creative test method for post-tensioned prestressed frame is presented in this paper. In the test, the stationary supports at the column base are simulated and the forces at the column base can be tested while the two column bases are not connected with concrete beam. The prestressed secondary moment and the weight-produced moment are established by adjusting the support device at the column base. In this paper, the necessary conditions of the method and the basic process are recommended. It is proved theoretically that the prestressed concrete frame built by this method is equivalent to that used in practice.     

The Experimental Study on Size Effects on Axial Compression Performances of Reinforced Concrete Column under Repeated Load

The size effects on axial compression performances of reinforced concrete column under repeated load are needed. Specimens were designed and tested in accordance with the relevant similarity, whose geometric dimensions are: 400 mm×400 mm×1 200 mm, 600 mm×600 mm×1 800 mm and 800 mm×800 mm×2 400 mm. The result of the experiment, the failure characteristics, crack development process, strength, peak stress, peak strain and stiffness of various specimens were comparatively analyzed. The results show that, within size range of this test, size effect exists on performances of columns.     

Discussion on the Secondary Moment of Prestressed Frame

The secondary moment of prestressed concrete frame is different from that of continuous beam. In this paper,the principle and calculation method of equivalent load secondary moment and axial secondary moment are discussed,and the infection of secondary moment in moment modulation is analyzed,together with the suggestions of moment modulation for prestressed concrete frame with adopting the total control. The suggestions would be able to distinguish the advantageous and disadvantageous effect of secondary moment. Some helpful advises for moment modulation design are given in this paper.     

Study on the Application of Large-span Prestressed Concrete Frame in Added Floor and Rebuilding

Around the reconstruction design of the Popular Science Image Building of the Southwest Hospital, the advantage of prestressed concrete frame used in the rebuilding was approved. At the same time, the problem in the prestressed frame design was pointed out. In the end, the method to decrease the moment in the column had been put forward.     

Curvature Force Method for Nonlinear Analysis of Prestressed Concrete Frame

In this paper, based on the structure characters and load applying means, a method called as curvature force method is put forward and proved in the nonlinear analysis of bonded prestressed concrete frame. Based on the nonlinear program, the simulation calculation was carried out on test results of two prestressed concrete frames by this method. The results from calculation are identical with the experiment ones. So it may be added to the methods for the nonlinear analysis of prestressed concrete frame.     

Probability Analysis of "Strong Beam and Weak Beam" and Axial Compression Ratio in RC Frame

In the view of reliability calibration, this paper analyzes the probabilistic sense of the provisions of "Strong Column and Weak Beam' and axial compression ratio in aseismic criteria (GBJ 11 89), which demonstrates that there is much difference between different aseismic ranks of RC frame. The authors suggest that it is possible to make axial compression ratio larger by adjusting the moment capacity ratio between column and beam. Finally, the direction and method of further studies are proposed.     

Comparative Study on Plastic Hinges of Prestressed Concrete Frames Under Vertical or Horizontal Loads

In With one-storey, two-span prestressed frames, a comparative study is done between under vertical and horizontal loads. The studies include the pattern of the plastic hinges occurring and, the demanded and available rotational capability of the hinges in critical sections. The relative height of compression zone and prestressed degree are considered. The result indicates that there is much difference in the pattern of the plastic hinge occurring when each plastic hinge has enough rotational capability. The beams can finish a full redistribution of internal force under vertical loads, but not under horizontal loads. Moreover, as increasing of the relative height of compression zone, a stronger rotational capability of hinges will be demanded to finish a full redistribution under vertical loads when a weaker rotational capacity will be needed under horizontal loads.     

The Effect on the Column Moment Considering Compress of Prestressed Concrete Beam

Axial compress is produced by the tension of prestressing beam, which engenders the third moment of column. And the third moment is always ignored in design. The thesis analyses elementarily the third moment of column and finds that the third moment must be taken seriously in some condition, and it is not the same value as the manner of tensions is different . As a result, some helpful conclusion and suggestion are presented.     

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.     

Contrast Analysis of Mechanical Behavior of Confined Concrete with Stirrups and CFRP Under Axial Compression

Aiming at confined concrete with stirrups and carbon fiber reinforced plastic(CFRP) respectively, the major influence factors of mechanical behavior of confined concrete under axial compression were studied based on reported experimental data. The equations for calculating the peak stress, peak strain and ultimate strain were proposed respectively for confined concrete with stirrups and CFRP. Contrastive analysis shows that the behavior of confined concrete with stirrups is better than confined concrete with CFRP in low characteristic value, whereas the conclusion is contrary in high characteristic value.     

Stress-Strain Model of FRP-Confined Concrete Column under Axial Compression

Stress-strain mathematical model of FRP-confined concrete plays an important role in civil engineering, and it should be well understood. Based on first region slope, turning point coordinate and third region slope, the development of stress-strain curve of FRP-confined concrete column is analyzed, and conditions which ideal mathematical model need to meet are point out. A new composite exponent-line model is proposed, which overcomes the weakness of conventional model and is available for both hardening and softening type stress-strain curves. Approaches to determine parameters of the proposed model are presented. Finally, the capability and accuracy of the proposed model in predicting the complete stress-strain process of FRP-confined concrete under axial compression are demonstrated through comparisons between predictions of the proposed model and test results.     

Experimental Study on a Prestressed Frame of Two Spans Under Unsymmetric Load

By the experimental study on a full-dimensioned prestressed frame of two spans, the relative factors are analyzed such as relative height of equivalent compression zone in critical section, secondary moment, ratio of beam rigidity to column and development of cracks in the top of columns etc., which influence the moment distribution of the post-tensioned prestressed concrete frame from the side of internal force redistribution. It is believed that that the factors of relative height of concrete equivalent compression zone and secondary moment influence the moment modulation in most degree, and ratio of column rigidity to beam also plays a part in the moment modulation to some extent. Second, the plastic joints of frame with excessive spans exit in the span which endure the whole load, at last the whole frame is destroyed because of the destruction of the loading frame, the influence to the non-loading span is little.     

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.     

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.     

A Study on the Test Method of Post-tensioned Prestressed Concrete Continuous Beam

A test method of post-tensioned prestressed concrete continuous beam is presented in this paper.In the test,the prestressed secondary moment is established by adjusting middle support height.The prestressed concrete continuous beam built by the method is equivalent to the beam in practice.     

Microcracking and Chloride Penetration of Concrete under Uniaxial Compression

A non-destructive method of evaluation of specific crack area was used to characterise microcracking in concrete prisms during uniaxial compression loading and unloading. Chloride profiles were also measured after the same concretes were exposed to chloride environment. The relation among microcracking, stress-strength ratio and chloride penetration of concrete were analysed based on the experimental results. Under compressive load, the apparent chloride diffusion coefficient decreases until about one third of the ultimate load. Further increase of compressive load improves the chloride diffusion coefficient again. There is a close link between microcracking and stress-strength ratio. The index of specific crack area can be used to indicate the microcracking and study chloride transport behaviour into concrete under the influence of microcracking.     

Suggestion for Moment Modulation of Prestressed Concrete Continuous Beams

Based on the information from China and overseas,a design suggestion for moment modulation of post-tensioned prestressed concrete continuous beams with bond has been put forth in this paper. The result calculated by the suggestion is consistent with the result of varying rigidity method.     

Measurement and Analysis of Prestressed Concrete Flat Beam- Waffle Slab System During Prestressing

During the pre - stressing of the unbonded prestressed concrete wide flat beam - waffle slab system, the displacements and strains of slab and the prestressed concrete beams were site - measured and the results were analyzed. The prestressing construction was simulated by finite element program. The prestressing efficiency of the unbonded prestressed concrete wide flat beam - waffle slab system was discussed. It indicates that the prestressing efficiency was affected by the in -plane stiffness of slab.