| At present,prefabricated prestressed concrete(PC)girder is widely used in bridge engineering.However,in the normal operation of the bridge,due to the degradation of material performance,poor construction quality,excessive overloading of vehicles and other factors,these structures will have different degrees of cracking damage.In order to analyze the static and dynamic stiffness of the cracked prestressed concrete box girders bridge structure,many scholars at home and abroad have studied the development of stiffness of scale-down mode,however,full-scale model testing cannot be completely replaced by scale-down testing because of material component characteristics and size effects.In addition,the analysis of static and dynamic stiffness degradation of full-scale assembled prestressed concrete(PC)girder with cracking damage in service is a hot issue,and the research on the the normal service limit state bearing capacity by using the dynamic methods and the relationship between the static and dynamic stiffness and frequency are also one of the hot issues.Through the analysis of static and dynamic test of full-scale prestressed concrete(PC)girders from cracking from failue,it is necessary to study a simple,convenient and effective method to evaluate the stiffness and bearing capacity of the prestressed concrete bridge in service.In this paper,three 30 m full-scale prefabricated prestressed concrete box girders are tested objects,and the static and dynamic load alternation tests under different load conditions are carried out.The degradation process of static and dynamic stiffness of full-scale box girder is studied.The main research contents of this paper include:(1)Based on Euler Bernoulli beam,this paper analyzes the influence of simply supported beam on the calculation of dynamic and static stiffness under the supported elastic support and rotation constraint,calculates the static stiffness and static stiffness reduction coefficient of simply supported beam through the mid span deflection,and calculates the dynamic stiffness and dynamic stiffness reduction coefficient of simply supported beam through the frequency;(2)In this paper,the static and dynamic alternation tests under different load conditions are carried outon the existing cracked prestressed concrete simply supported box girder.The static and dynamic parameters of the girder structure under different damage conditions are obtained.The static and dynamic stiffness of the structure are identified.The change law of the static and dynamic stiffness with the damage condition is studied,and the reasons for the difference are analyzed;(3)Based on the ANSYS finite element software,the finite element model of prestressed concrete simply supported box girder is established,and the nonlinear static analysis and modal analysis of the full-range from cracking to failure are carried out.The deflection value and natural frequency of midspan under various load conditions are obtained,and the relationship between static and dynamic stiffness and frequency under the influence of bearing and local damage is identified and analyzed,and compared with the test results,a method of inferring the static stiffness of the actual girders using the frequency ratio is proposed.The results show that the dynamic stiffness of complete girder can not be considered as a simple support condition,and the first mode frequency is more sensitive to cracking than the second mode frequency;the final static stiffness of the test girder is about 30% of the initial static stiffness,and the final dynamic stiffness of the test girder is about 84% of the initial dynamic stiffness.Through the finite element analysis,the final static stiffness attenuation coefficient is 0.180,and the final dynamic stiffness attenuation coefficient is 0.80.The research results can provide a reference for the stiffness evaluation and structural performance evaluation of existing damaged girders,and can also provide ideas for the evaluation of the actual bridge bearing capacity. |
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