Research On Frictional Prestress Loss In Curving Hole Of Long-Span Prestressed Concrete Bridges

With the continuous development of prestressed concrete technology,the longspan prestressed concrete bridges,such as continuous beam bridges and rigid frame bridges,are widely used in practical engineering.Influenced by various factors,including bridge design and construction methods,load and temperature conditions,as well as concrete creep and shrinkage,the diseases of bridges in service have been increasingly highlighted,which are mainly manifested in the continuous deflection at mid-span and cracks on concrete box girders,etc.Since they would endanger structural safety and working life mainly due to the loss of effective prestress.Prestress loss,caused by frictional resistance,in curving hole of prestressed concrete bridges was systematically studied and discussed on the combination of theoretical analysis,finite element simulation and experimental research in this paper,and the main research contents are as follows:Firstly,Hertz elastic contact theory and the contact characteristics between prestressed tendon and curving hole were applied to analyze the irrationality of code formulas used to calculate the prestress loss in curving hole,in which the concrete is considered to be rigid,so the contact boundary between tendons and concrete remains unchanged,and the contact pressure is assumed to distribute uniformly.Furthermore,experiments were conducted to determine the irrationality of formulas employed to calculate the multi-curve prestress loss according to the superposition principle of curving hole angle.Tests on Polyurethane specimens were carried out under different conditions to investigate the contact between tendon and concrete curving hole.Then the CT scanning technology was adopted to obtain horizontal and vertical displacement variations in the corresponding control points of loading section,and these variations were then applied in the finite element model to explore the variation law of specimens normal stress with the effect of three main parameters,including contact angle,radius of curvature and tension.Meanwhile,we discussed the variation of contact stress curves under different conditions and the effect of factors mentioned above on contact stress,distributed pressure hypothesis in different forms were also proposed to calculate the prestress loss in curving hole.The reliability and practicality of formulas proposed in this paper were verified in comparison to code formulas.Finally,a series of strain gauges were attached to prestressed tendons in a practical bridge engineering,in which tendons were tensioned uniformly under multi-leveling loading.By comparing the recorded effective prestress,calculated value derived from code formulas and proposed formulas,the accuracy and practicality of proposed formulas were verified,general good results suggest that the proposed formulas could be utilized to calculate prestress loss in curving hole with relatively large angle and multi-curve,since they could yield good prediction.Moreover,super-long prestressed tendons and curving hole with multi-curve should be prudently employed in design of prestressed concrete structures,in order to avoid large prestress loss caused by frictional resistance.