| Due to the internal defects of materials,environmental impact,external load and so on,the existing concrete bridge is in the stage of cracked work.The crack of beam body is relatively stable under the action of ordinary vehicle load,but the crack situation will be greatly different under the action of unconventional overloaded customized transport vehicle(hereinafter referred to as CTV)load.CTV load is a kind of special vehicle load whose axle number,wheelbase and load capacity exceed the bridge design code.When CTVs load acts on the bridge with cracks,it will have a great adverse effect on the crack performance.In order to explore the development performance of existing cracks in typical medium and small span bridges under the load of CTVs,and to provide suggestions for the management,reinforcement and maintenance of relevant departments of large transport,this paper studies the cracks of concrete bridges with cracks based on the finite element software.Firstly,based on the theory of concrete fracture mechanics,the appropriate fracture model and calculation method of stress intensity factor are selected,and according to the test data of relevant scholars and Bazant size effect rate,the initiation fracture toughness and instability fracture toughness of typical medium and small span bridges are calculated,Secondly,based on the finite element software ANSYS,the solid vehicle-bridge coupling vibration analysis system is established,and the refined anslysis of the beams with cracks is carried out.Then,through the indoor hollow slab failure test and field load test,the correctness and applicability of the established solid vehicle-bridge coupling vibration analysis system is verified.Finally,an assessment system of large transport vehicles crossing the bridge is established to calculate the stress intensity factors of medium and small span bridges under the action of five CTVs,and the corresponding bending moment value of the mid span section of the beam under the initiation fracture toughness and instability fracture toughness are calculated based on the durability consideration,they are taken as the control bending moment of the two stages of crack development.The main conclusions are as followed:(1)For engineering application,it is a convenient and accurate way to calculate the fracture parameters of typical medium and small span bridges by using the existing test data and Bazant size effect rate.It can solve the problems of high cost,long time and difficult data measurement of full-scale beam fracture parameters;(2)For the local refinement theory of fracture mechanics,the solid vehicle-bridge coupled vibration analysis system can be integrated with it,and the stress intensity factor time history of crack tip can be calculated accurately.Because of the advantages of ANSYS parametric modeling,the established assessment system of large transport vehicles crossing the bridge has high convenience and practicability;(3)The stress intensity factors of the crack tip in the middle span of the ordinary reinforced concrete bridges under the action of the moving CTVs will reach the initiation fracture toughness,but will not reach the instability fracture toughness;the prestressed reinforced concrete bridges,due to the existence of prestress’ s external force compression,makes the crack in the closed state under the action of the CTVs of,and the crack will not crack;(4)Due to the different axle number and axle load of different span bridges at the most unfavorable moment,the control CTVs models of crack performance are different: the concrete simple supported hollow slab bridges are controlled by the CII,the prestressed concrete simple supported hollow slab bridges are controlled by the CII except the 20 m span is controlled by the CIII;the prestressed concrete simple supported T-beam bridges are controlled by the CIV,and prestressed concrete continuous small box girder bridges are controlled by the CV;(5)For ordinary reinforced concrete bridges,when the most unfavorable positive moment in the midspan section reaches 0.32～0.39 times of the design vehicle load effect,the existing cracks in the midspan section will crack;when the most unfavorable positive moment in the midspan section reaches 1.02～1.25 times of the design vehicle load effect,the concrete may have obvious cracks,which will affect the durability of the bridge structures;(6)Based on the linear elastic fracture mechanics,a fast assessment method for the passage of large transport vehicles of medium and small span bridges is established.The assessment system is simple and convenient to operate,and the physical significance of the assessment index is clear.It can provide technical support and practical reference for relevant departments to formulate the passage scheme of large transport vehicles. |
