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The Prestress Tensioning Time Research of Cast-in-place Prestressed Concrete Continuous Beam Bridge

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Tutor: YuDeHu ZhangTongBo
School: Qingdao Technological University
Course: Structural Engineering
Keywords: cantilevered concreting method,prestressed tensioning,tensioning time,bridge for
CLC: U441.5
Type: Master's thesis
Year:  2010
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Nowadays, long span continuous beam bridges are always constructed with cast-in-place cantilever construction technology, which could be finished in a compared short time without lower support beams, but has some possibilities of accidents because of unreasoned prestress tensioning. Therefore, we should keep on theory researching of prestress tensioning in construction cantilevers long span continuous beam bridges, to make sure construction schedules of prestress tensioning in different air temperature, to find out the rule of time influencing on prestress tensioning, to reinforce the control of bridges¡¯. This is the background of this research.First, based on maturity grade theory, established the relationship of concrete compressive strength and maturity. According with different curing temperature in different construction condition, this article gave estimating formulas of early concrete strength, to lay a foundation of theoretical analysis and numerical calculation of subsequent chapters.Second, introduced the basic concept of prestressed concrete, described types of construction load in prestressed reinforced concrete structure¡¯s cantilever construction period, explained internal force analysis method of stress system of bridge, established calculation model of familiar prestressed continuous beam bridge, to lay a foundation of load effect analysis in subsequent chapters.Third, according to strength failure criterion, in add to considering design condition of prestressed concrete beam bridge in construction period, worked out a method to determine concrete strength while prestressed tensioning, with an engineering example to calculated. Then this article analysis the rule of the form of prestressing tendons to influence tension strength.Forth, considering factors that make prestressed tensioning time uncertain, according to reliability theory, this article pointed out instead of take strength only into account, which was not safe enough, we should consider reliability index and strength all together. Then work out prestressed tensioning time determination method, to coach engineering practice.At last, beginning with calculation method of concrete vertical deformation and summing-up of project experience, to find out main factors influenced concrete vertical deformation. Then illustrated these main control factors with practical engineering project of Xuluote bridge in passenger dedicated line from Shijiazhuang to Wuhan.
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