Study On Bearing Capacity Degradation Of In-Service PC Plate Beam In Seasonal Frozen Area Based On Crack Calculation

As a common structural form of bridse ensineenns,prestressed concrete beams are mostly used for medium and small span bridges in highway networks.During the service of the prestressed reinforcement concrete bridge in seasonal frozen area,the components of the bridge will gradually deteriorate under the influence of natural factors such as climate and environment The increasing load of automobile makes the mechanical properties of the bridge members attenuate,and the difference between the desisn load of the early bridge design code and the current code leads to the working of the prestressed concrete bridse in the stage of crack.The existence of cracks directly affects the safety and durability of bridges,and the structure should be repaired and reinforced.Before the decision of the bridge reinforcement it is necessary to make a scientific evaluation on the working state and the remaining service life of the cracked prestressed concrete in order to detennine the maintenance plan and the priority of the maintenance.Therefore,it has important engineering application value to evaluate the bearing capacity of the cracking prestressed concrete beams and the remaining service life.Based on Transportation Science and Technology Project of Heilongjiang Province Transportation Hall of China "Evaluation Of Existing Bridge Bearing Capacity And Reinforcement Technology Research(201512)"and "the Fundamental Research Funds for the Central Universities(2572017AB01)",The experimental study on the degradation mechanism of the nexural capacity and shear capacity of ten prestressed concrete hollow slab beams in this paper,which has been in service for 20 years in the frozen area.Based on the bending and shear static load tests of the beams,the variation law of stress response of prestressed concrete test beams,bending and shear bearing capacity,the variation law of the width of the bending crack,the influence of vertical cracking in bending area on deformation of sectional bending stiffness.the variation law of the width of the diagonal crack and the influence of diagonal cracking in shear compression zone on deformation of sectional shear stiffness have been analyzed.Tlie special inspection,material mechanical performance and bearing capacity of prestressed concrete hollow slab test beams for 20 years in the frozen area were carried out.Based on these data of material mechanical performance,the ANSYS finite element model is established.By comparing the measured value of the load test with the calculated value of the finite eleiment,the stress response state and bearing capacity of the prestressed concrete hollow slab test beam for 20 years in the frozen area are evaluated;Considered the stress redistribution between different types of reinforcements in the beam and introduced the stress distribution coefficient,the numerical model of the calculation of the bending crack width of the prestressed concrete beam is established based on the bond slip theory;Combining with the theory of cross section nonlinear analysis and calculation,the variation law of the bending stiffness of the prestressed concrete beams during the whole process from the section cracking to the failure stage is studied.The calculation method of bending stiffness loss of prestressed concrete beams with crack characteristics as the parameters i5 proposed;The influence of different shear span ratios on the development of oblique cracks in the shear zone of prestressed concrete hollow slab beams is analyzed.The calculation formula of the diagonal crack width of prestressed concrete beams with the shear span ratio is established;Based on the existing shear stiffness degradation model and the calculation formula of the diagonal crack width,an analytical model for calculating the effective shear stiffiiess of prestressed concrete beams with the maximum width of diagonal crack is established.The effect of the crack on the shear stiffness is quantitatively analyzed;According to the environmental characteristics of the frozen area,a calculation model for the performance degradation of concrete and prestressed reinforcement are established.Combined With the principle of structural design,the calculation model of time-varying resistance degradation of prestressed concrete beams is given.The time dependent reliability is analyzed on the basis of operating load,and the prediction of remaining service life of prestressed concrete beams in China's frozen area is also carried out.Based on the experimental research and numerical analysis of the prestressed prestressed concrete beams in seasonal frozen area,the calculation formula and model are established in this paper,which provides the basis for the design checking calculation,reinforcement and maintenance and the maintenance and management strategy of the prestressed concrete beam bridge in seasonal frozen area.