Carrying Capacity Assessment Of Jian Ganjiang Highway Bridge Based On Static And Dynamic Loading Test

Bridges are important infrastructure concerning notional economy and people's livelihood.The carrying capability and traffic capability of bridges are critical to keep smooth traffic flow.As time goes on,more and more bridges in service are damaged,leading to insufficiency structure function and the decrease of carrying capacity,which affect the normal service of bridges seriously.Therefore,the bridge assessment is necessary to get the real working states of structures.The carrying capacity assessment is the key content of bridge assessment.Taking the Ganjiang highway bridge located in Jian city,Jiangxi Province,as an example,the carrying capacity assessment of the bridge is investigated in this thesis through the field static and dynamic load tests.Appearance inspection and nondestructive detection are first performed for initial qualitative evaluation of carrying capacity.Thereafter,the field static and dynamic tests are carried out.The loading properties,dynamic characteristics and impact factor of the bridge are obtained to assess the carrying capacity.The initial finite element model(FEM)is established based on the original design drawings.The sensitivity analysis of natural frequency to structural parameters is studied to select the sensitive parameters.The initial FEM of the bridge is then updated by adjusting the parameters to the best fitting the dynamic characteristics identified from field vibration measurements.The updating FEM that reflects the current states of the bridge is used to further assess and predict the future carrying capacity.The proposed the carrying capacity assessment method and process can be referred to other existing bridges.The main work of this thesis is as follows:1.Visual inspection for the Ganjiang bridge is performed and structure damage states are investigated.Nondestructive detections including concrete strength,carbonation depth,concrete thickness and rebar corrosion are carried out.According to the bridge evaluation standard,the comprehensive assessment is performed on structural components of the bridge for further assessment of carrying capacity.2.The initial FEM of the Ganjiang bridge is established based on the original design drawings.The static and modal analysis is carried out accordingly.The static analysis is to calculate the influence line that is used to get the loading section loading efficiency for the static load testing,while the modal analysis is to get the measurement points for the field ambient vibration testing.3.The field static loading test is performed on the Ganjiang bridge to get the strain and deflection under vehicle loading from each measuring point.Combining the analysis results of initial FEM with measured results,the preliminary assessment of carrying capacity is investigated.The dynamic strain,acceleration and impact coefficient are obtained by vehicle excitation tests.By using the ambient vibration measurements under operational conditions,the dynamic characteristics are identified by both peak-picking method in the frequency-domain and stochastic subspace identification in the time-domain.The sensitivity analysis of natural frequency to structural material and geometry parameters is studied to select the sensitive parameters by using the initial FEM of the Ganjiang bridge.The initial FEM of the bridge is then updated by adjusting the parameters to the best fitting the identified dynamic characteristics.The updating FEM reflects the current states of the bridge.4.By using the modified FEM,the detailed assessment and prediction of carrying capacity for the Ganjiang bridge can carried out.Internal force of the controlled sections under static loadings according to new bridge design standard is calculated,which is compared with the old bridge design standard that was used to design the bridge at that time.The degradation of FEM parameters is used to simulate the structural damage.Based on the modified FEM,The equivalent check coefficient method is applied to predict the carrying capacity of the bridge for the increase in the future traffics.It is demonstrated that the modified FEM have more advantage in carrying capacity assessment of existing bridges.