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.     

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.     

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.     

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.     

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 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.     

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。     

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.     

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 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.     

Analysis Theory of Unbonded Prestressed Concrete Continuous Beams

In this paper, the energy method has been used to study the change of the secondary moment of unbonded prestressed concrete continuous beams and it has been contrasted with bonded prestressed beams. The question, whether the secondary moment changes or not while loading, was answered. It shows that the primary secondary moment does not change when increment method is adopted to study the beams, but the total secondary moment will change while the force in prestressed reinforcement changes.     

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.     

Study on the Key Construction Techniques about the Prestressed Transform Beam of Chongqing People''s Mansion

In order to ensure the construction quality of the massive prestressed transform beam, to prevent and control the cracking before tensioning ,the technology of casting ,methods of temperature and crack controlling are carefully analysed and theoretical calculation is carried out as well as the temperature inspection during construction ,all of which have effective results. Some prestressed construction points of transform beam are also introduced in this article, and reference advices are given at last.     

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.     

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.     

The Effect of Axial Compression on the Prestressed Concrete Frame under Vertical load

For prestressed frames, the axial compression ratio will affect not only the ductility of structures but also the structural internal force.Based on the computer-calculation for four groups of 24 prestressed frames combined with the references, in this paper, the effects of axial compression ratio on the prestressed frames are studied and discussed through three aspects: the second-order effect, the axial deformation of frame-columns and the comparison with ordinary concrete frames.The study results show that the effects of axial compression ratio on the prestressed frames and the ordinary concrete frames are basically consistent, but there are some self-born characteristics.As a whole, the effect of axial compression ratio on the prestressed frames is more notable than that on the ordinary concrete frames, but under common situation the effect is small.     

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.     

体育馆大跨度预应力次梁楼盖竖向振动模态分析

以重庆市铜梁县新城核心区小学建设项目3^#楼（体育馆）工程为背景,对其大跨度预应力次梁楼盖竖向振动模态进行模拟分析,并与实测结果相比较,评价其控制竖向振动舒适度的效果。根据建模思路精确建立的该大跨楼盖有限元模型,其模态分析结果与模态实测结果接近,相对误差约为5%;模拟分析及工程实测结果表明,该大跨楼盖前三阶振型均以竖向振动为主,结构自振基频满足我国现行相关规范的要求,竖向振动舒适度符合标准;与无底板的大跨次梁楼盖相比,增加底板后,其增幅最小的一阶频率增长了19.9%,表明增加底板可有效地控制大跨度预应力次梁楼盖的竖向振动。     

Finite Element Simulate Analysis of Small Span-to Depth Ratio Coupling Beams with Special Reiforcement

Test investigations show that the reinforcement scheme with adding diagonal and rhombic bars to traditional reinforcement in the foundation is an ideal way, for the seismic performance of small span-to depth ratio coupling beams with this scheme is better than that of traditional reinforcement. Because the regions in the small aspect ratio coupling beam belong to D-regions, in which the Bernoulli hypothesis of plane strain distribution is invalid, the traditional bending theory can not be used. This paper simulates the coupling beam through non-linear finite element analysis program, and contrasts the analysis result of the bar's stress distribution with test result. The contrast results confirm that it is a valid way to analyse the bar's stress distribution in this coupling beam through non-linear finite element analysis program.     

施工阶段大跨径预应力混凝土刚构桥腹板开裂机理

进行了大跨径预应力混凝土刚构桥腹板开裂机理研究,基于弹性力学平面问题分析方法,推导了集中荷载作用下的板件应力函数表达式,绘制了不同受压边长与集中荷载长度比（d/a）下的横向应力曲线,拟合了集中荷载作用下构件的横向应力求解函数,构造了混凝土刚构桥腹板在预应力集中荷载作用下等效压力矩形的选取方法,并基于平面应力的表达式提出了在三维情况下沿预应力轴线的横向应力计算方法。通过建立某预应力混凝土刚构桥0~3#段实体有限元模型,分析施工过程中刚构桥混凝土腹板在不同等级预应力作用下的开裂情况。结果显示：有限元裂缝模拟与实桥腹板开裂范围一致,有限元应力分析结果下限值与推导的横向应力求解函数计算结果接近,变化趋势一致,印证了横向应力函数求解方法的正确性。