Mechanical Behavior and Techno economic Analysis of Twice prestressed Simply Supported Composite Beam

Excessive creep camber of prestressed concrete bridge would result in risk on the traffic safety in high speed railway. To control creep camber of presstressed concrete bridge, a new twice prestressed technology was proposed to presstressed concrete beam. Four twice prestressed simply supported box girders with different prestressed degrees were designed as an example. Its section stress, strength and crack resistance in different construction stages were analyzed. Compared the creep camber between conventional prestressed simply supported concrete beam and twice prestressed simply supported composite beam with the same prestressed steels, it was shown that twice prestressed composite beam has a smaller stress gradient. And the creep camber decreased approximately 40% to 60% with building height reduction, as well as some 10% energy saving and some amount of concrete.     

Design and Test of an Exceedingly-long Prestressed Workshop Floor

Based on the project of a prestressed concrete beam-slab structure,this paper introduces the optimum design of a four-spanned exceedingly long prestressed floor. Different schemes,such as the scheme of the prestressed major beam,the scheme of the prestressed secondary beam with the same span and the scheme of the prestressed secondary beam with different spacing,are compared and analyzed in this paper.Meanwhile,various methods of the exceedingly treatment for long prestressed reinforcement are compared.Finally,based on two prestressed beams,the prestress loss,the prestressing value at the ends of the beam and the deflection in the midspan of the beam are detected during the tension and anchorage stage in order to verify the results of the theoretical analysis.     

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.     

RESEARCH ON WALL BEAM OF PARTIALLY PRESTRESSED CONCRETE

In this Paper,multistoryed buildings of brick and RC floor slab construction are put up on frame beam of 12. 6 m partially prestressed concrete.A test and analysis is carried out on site.It provides a new scheme for multisto-reyed and highrise buildings with beam of transitive force and transfer floor.     

A forward algorithm for prestressed construction process of large-span suspendome based on the equivalent pre-tension

To accurately simulate prestressed construction process of large-span suspendome, the initial state of construction process according to practical construction sequence is established, and the construction mechanical analysis for prestressed construction process is especially studied. Features of prestressed construction process of large-span suspendome are summarized, and the insufficiencies of the application of state variable superposition method, back analysis method, birth and death element method are analyzed. Combined with nonlinear finite element analysis method, forward algorithm for prestressed construction process based on the equivalent pre-tension is proposed, and the specific application method and procedure are given. Changzhou stadium steel roof engineering is taken as an example to verify the practicability and applicability of forward algorithm for prestressed construction process. The conclusion is that, using forward algorithm for prestressed construction process based on the equivalent pre-tension, the structure state of each construction phase can be accurately tracked, and the nonlinear contact of strut and rigid framework, interactive impact of cable force, conversion of temporary structure system, and structural geometric nonlinearity can be comprehensively considered.     

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.     

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.     

Large Span Concrete Box Beam Construction Technology

Combined with the engineering practice, the method of large span post tensioned prestressed box beam construction technology was introduced, which can provide the reference for the similar project.     

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.     

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.     

多点锚固体外无粘结CFRP预应力加固RC梁的抗弯性能

在梁侧或梁底用波形齿横向张拉CFRP片材并锚固的体外预应力加固混凝土结构技术,对3根完全相同的7 m跨T形截面梁进行加固：其中2根梁侧面加固;1根梁底部加固。试验表明：多点锚固体外无粘结CFRP预应力可以依据构件的弯矩来调整各段的加固量从而更有效的利用CFRP材料的高强性能;梁底与梁侧加固对提高构件的抗弯刚度差别不大;波形齿能彻底解决预应力CFRP片材的锚固问题。以该3根加固梁的试验结果为基础,提出了梁体极限状态下塑性绞区长度的体外无粘结预应力碳纤维加固受弯构件的抗弯承载力公式,以及考虑二次效应的有效惯性矩法的挠曲变形的计算公式,通过与试验值的对比分析可知,所提出的方法可供设计参考使用。     

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.     

Analysis and Optimization of Tension Sequence of Prestressed Reinforcing Steel Bars in Concrete Beam

Post-tensioned prestressed concrete beam in tensioning of prestressed reinforcement is based on the symmetry principle to determine the tensioning sequence.Simulation of the tensioning process of a 54m span post-tension concrect beam of a Prestressed Concrete Frame Structure in Fuxin was conducted with the finite element analysis program ADINA. With two different tensioning schemes,the influence of the tensioning sequence on deformation is calculated and then compared with the tensioning one by one in order the tensioning sequence is optimized.     

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.     

Finite Tension Element Analysis of Post TensioningPrestressed Concrete Hollow Slab

The prestressed tension is an important part of the prestressed concrete component construction.In order to find out the influence on the concrete hollow slab of different tension sequence,in this paper,the 30 m assembled post tensioning concrete hollow slab is simulated by the means of finite element analysis software ANSYS. The variation of the hollow slab's stress and strain are discussed according to the result of the different tensioning sequence, then, the reasonable sequence of tensioning prestressed steel wires is put forward.     

Construction Stage Analysis on Replacement of Closure Segment in Prestressed Concrete Cable-stayed Bridges

To deal with failure of wet joint between a closure segment and its neighboring segments of main girder in an existing prestressed concrete cable-stayed bridge, the technology on replacement of closure segment was presented. In order to analyze structural characteristics of this technology, its technical approaches and construction key points were introduced. Then a FEM model for a typical prestressed concrete cable-stayed bridge was established, and a construction stage analysis method was given in detail, including establishing a structural basement calculation model for replacement of closure segment and simulating its construction procedures. Based upon calculation results, variations of some structural state parameters with construction stages, such as deck deflection of main girder, longitudinal horizontal displacement at the top of pylons, cable forces, were analyzed. The results showed, this method could reflect actual change process of structural state and existing inspected results of cable-stayed bridge, and FEM results could well meet with construction monitoring results during replacement of closure segment. Thus variations of structural characteristics with construction stages could actually be revealed. This method could provide references for design and construction control of replacement of closure segment in existing prestressed concrete cable-stayed bridges.     

Establishment of Pre-stress in Flat Beam of Tube-in-tube Structure

This paper introduces the analysis and test of prestressed flat beams in tube-in-tube concrete structures at different construction stages; moreover, the corresponding structural analysis models with FEA program are set up. Through the comparative analysis between the results of construction field test and that of calculation with FEA method, it proves the reliability of the primary design method; meanwhile, it also indicates that establishment of prestressing force and prestressed effects in similar structures is a complex procedure and should be noticed.     

Numeric Analysis of the Dynamic Performance of a Prestressed Concrete Beam

The finite element of a prestressed concrete (PSC) beam is analyzed in a case of diverse prestressing forces. The mechanical model applied is that advanced by Clough for a concrete beam bearing axial force. The results indicate that the beam frequencies decrease with increasing prestressing force. A dynamic experiment of a non bonded PSC beam was carried out to validate the veracity of the finite element analysis. Test beam frequencies increase with increasing prestressing force. The analysis model thus is unfit for frequency analysis of a PSC beam. The determinant factor of frequencies is analyzed, and the dynamic model is modified according to experimental results. The modified model analysis result shows that: the calculated frequencies of mode 1 agree with the test results well; the frequencies of mode 2 posses some errors; and, the modified model can reflect the direction of frequency change along with the change of prestressing force well.     

Analysis on Longitudinal Cracks and Deflection of the Pre-stressed V-shape Slab Roof Structure

In this paper, the finite element method is used to analyze the behavior of the prestressed V-shape Slab Roof structure, especially the effect of temperature change on the stress of slab. The calculated results indicate that when the temperature changes, the tensile stress at the lower extreme fibers of the flange plate near rib exceeds the tensile strength of concrete subjected to the combined action of triaxial stresses and results in the longitudinal cracks of the flange plate. The deflection analysis is based on the mechanical model of the prestressed V shape slab with the longitudinal cracks. The calculated results are in general agreement with the field observations.     

Temperature Field Analysis of Long-span Concrete Box Girders

Taking a two-lane extra large bridge as sample,it is to analyze the real time thermal field and thermal effect on a long-span prestressed concrete box girder. The obtained data is compared with the simulation which is based on a balancing theory of temperature distributions and exchange in box girder exterior surfaces. The results show that the proposed method can emulate the actual boundary conditions precisely, it can satisfy the design analysis requirement of the practice engineering. Based on the emulation of the temperature field, with the ANSYS secondary development technology, FEM modules are developed to analyze the thermal field of the prestressed concrete box girder bridges. The present examples show that the developed modules are effective and useful.