Research On Bridge Rapid Diagnosis Technology Based On Flexibility Coefficient

Traditional static loading test method for bridges is widely used at present,because of its reliability,availability and the technical theory of mature.However,the static loading test has the disadvantages of low test efficiency,interrupted traffic,and high costs.Dynamic loading test method has been rapidly developed due to its efficient and convenient means of testing.The inversion of the static mechanical properties of bridges using dynamic parameters has become a hot topic in current detection research.The flexibility coefficient is taken as the index,which is the norm of the modal flexibility matrix,and establishing the relationship between flexibility coefficient and the calibration coefficient in static loading test,in order to achieve rapid diagnosis and assessment of bridges.The modal and static analysis of bridges with different cross-sections and spans were conducted to obtain data on different damage conditions,such as frequency,mode shape and deflection.And calculate the flexibility coefficient and the calibration coefficient finally.The main work and achievements are as follows.1.Algorithms of the flexibility coefficient and the quality-normalized mode shapes based on mass changes were derived and summarized.And comparing the results of quality normalized mode shapes under different additional ways by numerical calculation.2.When the elastic modulus of the bridge decreases,the transverse joint damages,and cracks occur at the bottom of the mid-beam,the flexibility coefficient increases with the degree of damage.Therefore,the bridge structure can be monitored in real time according to the change of the flexibility coefficient.3.The ratio of the flexibility coefficient of the damaged structure to the intact is defined as the flexibility calibration coefficient.Calculation and analysis of dynamic and static parameters under different damage conditions,the results show that the flexibility calibration coefficient and the calibration coefficient are in a corresponding relationship.The calibration coefficient can be completely replaced by the flexibility calibration coefficient,which will provide new ideas for rapid diagnostic testing of bridges.4.The influences on the flexibility indicators under the changes of the position of the mode shape line,the change of the modal order and the change of the additional load are analyzed.The results prove that the flexibility coefficient is influenced by the position of the measured line and the additional load,and does not depend on the modal order.However,the flexibility calibration coefficient is completely unaffected by the above factors.Therefore,a convenient measuring line can be selected in the field test,and only the first-order modal parameters can be used to calculate the flexibility calibration coefficient accurately,which is more convenient for field testing.5.After analyzing the different spans of T-beam bridges,cored slab bridges and box-girder bridges,the calibration coefficients can be replaced by the flexibility calibration coefficients when the degree of damage is constant.Finally,the calculation and analysis of the practical data of a bridge in Hebei Province verify the feasibility of using the flexibility calibration coefficient instead of the calibration coefficient to evaluate the performance of the bridge structure.6.The relationship between the bending rigidity and the flexibility coefficient of the bridge structure is established and the two are inversely proportional to each other,which is in line with the physical meaning that the structural rigidity is inversely proportional to the flexibility.Further analysis of the relationship among flexibility coefficient,bending rigidity and calibration coefficient,which provides a new idea for rapid diagnostic testing of bridges based on flexibility coefficient.