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 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.     

Experimental Study on Moment Modulation of Prestressed Frames

Based on the experimental study of two prestressed frames in redistribution of Internal force, it can be concluded that the dominating influence factors on moment modulation are the relative height of equivalent compression zone, the secondary moment, the ratio of beam rigidity to column and development of cracks in the top of columns.The secondary moment is very important in modulation of frames. Especially, the secondary moment will governing the modulation when the relative height of equivalent compression zone is large enough.     

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.     

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.     

Inelastic Seismic Response of Ordinary Reinforced Concrete Regular Frames

With an inelastic dynamic analysis program developed by the authors, seismic response analysis of regular RC frames designed to Chinese codes in different earthquake fortification zones are carried out. The results indicate that the displacement responses of structures are improved due to the more rigorous limitation on the inter-story drift under frequent earthquakes in the revised codes. The frames in seismic-intensity-9 zone designed to the former codes and the revised codes form plastic energy-dissipated mechanisms mostly With beam hinges, which can satisfy the requirement of seismic performance expectably. The frame in seismic-intensity-8 zone designed to the former code forms a plastic energy- dissipated mechanisms mostly with column hinges and shows a risk of occurrence of story-sway mechanism, while the frame in seismic-intensity-8 zone designed to the revised codes exhibits a relatively improved seismic performance but still with excessive column hinges, which suggests a need to further increase the column moment amplification measures for this kind of frames. The frame in seismic-intensity-7 zone shows a somewhat improved seismic performance than the frames in seismic-intensity-8 zone, but the protection to columns by the seismic measures is sill insufficient, which indicates that the column moment amplification measures for this kind of frames should be enhanced further.     

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.     

Stability Behavior of Shuttle-Shaped Steel Lattice Columns With Bending Moment

The stability behavior of shuttle-shaped steel lattice columns subject to combined axial force and bending moment was examined through elastic buckling analysis and geometrically and materially nonlinear analysis. Firstly, the concept of section stiffness variation ratio is proposed for shuttle-shaped lattice columns and the elastic buckling behavior is discussed. Then, the effect of bending moment on the stability behavior of lattice columns is investigated, with the emphasis on the development of axial stress, bending stress and shear stress. The influence of column component spacing and diaphragm thickness on the stability bearing capacity is also analyzed. It is shown that the elastic buckling mode of the lattice column is dependent on its section stiffness variation ratio; for lattice columns with C-shaped buckling mode, the reduction in stability bearing capacity caused by bending moment is smaller than that of columns with S-shaped buckling mode; the maximum stability bearing capacity of the lattice column can be achieved by adjusting the column component spacing, and the spacing corresponding to the maximum capacity is basically consistent with the critical spacing for transformation of C-shaped buckling mode and S-shaped mode; and it is more effective to increase the thickness of columns with S-shaped buckling mode to get larger bearing capacity.     

Test and Finite Analysis to Non-strong Column and Weak Beam Concrete Frames

Through the test of two concrete frames under vertical load and nonlinear finite programme analysis,the performances of strong beam with weak column and equal strength column and beam are studied,such as ultimate load,deflection,displacement ductility,redistribution of internal force.When the reinforcement is proper,the research proved that strong beam with weak column" and "equal strength column and beam" have better displacement ductility and can realize full redistribution of internal force,the width of cracks and deflections can satisfy the rules of code for design of concrete structures.     

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.     

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.     

Experimental Research of Vertically-Loaded RC Joint of Local Transfer from Inclined Column with Different Angle to Beeline-Shaped Short Shear Wall

According to test results of two different angle specimens of local transfer RC joint from inclined column to Beeline-shaped short shear wall under vertical static loads and results of corresponding finite element analysis(ANSYS), fundamental behaviors of the joint are achieved for the change of the angle.The result indicates that there is much difference in the stress distributions of the transfer beam and short shear wall for different angles of inclined column, which shows that the larger angle, the more great tensile force and the earlier crack in the transfer beam and the lower capacity. Otherwise, the angle is smaller, the evener stress distributions in short shear wall, the later crack, the worse degenerate in the transfer beam and the higher capacity.Furthermore, the mechanical behaviors of the joint obviously followed the characteristics of a truss model.     

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.     

Seismic Assessment of RC Frame Structure Based on New Design Codes

The national structural codes GB50010-2002 and GB 50011-2001 have been modified in many aspects compared with the old ones. To verify the effectiveness of structural capacity design provisions in the new codes, firstly, two typical RC frame structures of Grade 2 in intensity-category 8 and Grade 1 in intensity-category 9 are designed according to the new codes. Then, nonlinear dynamic analyses of the two structures are carried out under excitations of several ground motions with the fortification and rare intensity levels. With the analysis results the availability of strong column weak beam is checked carefully, which is desirable with capacity design measures of RC frame in Chinese new structural design code. The conclusions drawn from the analysis are helpful to structural design and local modification of the codes.     

Influence of seismic fortification intensity for multilayer concrete structure performance

For multilayer concrete structure, the seismic ability of the ground floor column is very poor, improving the seismic fortification intensity of structure is adopted in this paper, the axial force, shear and moment of beam and column are calculated and analyzed in seven degree and eight degree seismic fortification intensity. Numerical results show that with improving the fortification intensity of the structure, the axial force, shear and moment of beam and column increase and the change of the ground floor is the most prominent. In earthquake the destruction of the structure mainly happens in the ground floor column, so this problem is solved fundamentally with increasing fortification intensity in architectural design.     

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.     

Calculation and Analysis on Critical Moment of Thin-walled Beams under Unequal End Moment

In this paper, comparing the bending-twisting model with the tension-bending one, the critical moment of the thin-walled beams under unequal end moment is derived easily by the improved CDC (column deflection curve) method based on the increment interaction equations of beam-columns.A simplified formula is presented and the calculated results show a good agreement with the numerical ones.     

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.     

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.     

A Study of Ultimate Loading Capacity of Eccentric Compressed Timber Column

In this paper, ultimate loading capacity of eccentric compressed timber column and elastic-plastic behaviour of the material of the cross section are considered.An approximate theoretic method dealing with the maximum mid-span deflection of the column when breaking is advanced.As a result, a formula calculating failure deflection of the rectangular cross section is derived. The results of theoretic calculation are well coincident with those of tests.