Identification Of The Effective Prestress In Prestressed Concrete Beam Considering Second-Order Effect Of Axiel Compressive Load

Prestressed concrete beam is a common type of our country bridge,owing to effects of load,environment,aging and corrosion of materials,etc,structure will inevitably produce accumulative damage and structure disease,decreasing load capacity,happen and even sudden accidents.Therefore,technical conditions of existing bridges need to be tested and evaluated regularly.Detection and assessment of existing prestressed concrete beam bridge mainly focused on visual statistics of cracks,Measurement of deflection and strain of structure by static loading test,evaluation of overall working condition of the structure by dynamic loading test.However,working condition of prestressed reinforcement in prestressed concrete beam bridge can not understand exactly by the methods for detection and assessment.The existing detection of prestress loss can only by burying sensors in structures during construction period and breaking test.These methods are expensive and risky.A non-destructive and economical testing method which can detected the existing effective prestress of prestressed concrete beam bridge accurately is needed.Considering the effect of shrinkage and creep and structural stiffness on the long-term deflection of beams,this paper derived a method for calculatingthe existing effective prestress based on measured deflection difference by starting from derivation process of deflection equations considering second-order effect of axiel compressive load of prestressed reinforcement.The evaluation method of effective prestress in this paper is verified by the solid finite element model.The main contents and results of this thesis are as follows:(1)Deflection analysis of prestressed beam considering second-order effect of axiel compressive loadPrestressed simple-supported girders are considered to be members under bending and axial compression,considering second-order effect of axiel compressive load of prestressed reinforcement,this paper derived deflection equations of prestressed simple-supported girders under working conditions of “self-weight” and “self-weight+ concentrated loads at midspan”.The correctness of deflection equations are validated based on engineering examples.The results show second-order effect of axiel compressive load of prestressed reinforcement increases the deflection of structure,deflection considering second-order effect of axiel compressive load at the key sections is about 6 per cent larger than that not considering,and the result is unsafe when bending down the structure.second-order effect of axiel compressive load of prestressed reinforcement is positively correlated with bridge span pretress,negatively correlated with the structural stiffness,independent of the external load on the beam.Secondorder effect in the middle of the span is less than the second-order effect in the quarter span under the same prestress level.(2)Identification of effective prestress in prestressed concrete beam considering secondorder effect of axiel compressive loadConsidering the effect of shrinkage and creep on the long-term deflection of prestressed concrete beams and second-order effect of axiel compressive load of prestressed reinforcement,the deflection equations of a certain moment under working conditions of “self-weight” and “self-weight+short-term concentrated loads at midspan” is derived.The effect of shrinkage and creep on the long-term deflection of prestressed concrete beams is eliminated by subtracting the vertical deflection under working conditions of “self-weight” form the vertical deflection under working conditions of “self-weight+short-term concentrated loads at midspan”.The relationship of deflection difference and effective prestress is established.Identification and calculation model of the existing effective prestress of prestressed simple-supported girders and continuous girders is established,and the possibility of identification model of effective prestress is verified by solid finite element model which according to engineering examples.(3)Identification of effective prestress in prestressed concrete beam considering structural damageBy introducing the theory of step stiffness,considering the effect of structural stiffness on the long-term deflection of prestressed concrete beams and second-order effect of axiel compressive load of prestressed reinforcement,the deflection equations of prestressed damaged simple-supported girders and damaged continuous girders under working condition of “concentrated loads at midspan” is derived.Calculation model of the existing effective prestress of prestressed damaged simple-supported girders and damaged continuous girders is established,and the possibility of identification model of effective prestress which considering stiffness damage is verified by engineering examples.