The New Method Investigation For Structural Damage Assessment Of Prestressed Concrete Box-girder Bridge With Incomplete Measurement

The methods of visual inspection or field test are mainly used to conduct the bridgestructural condition assessment. There are some limitations of these methods due to timeconsuming labor work and high cost. These methods cannot get the complete information ofthe structure and the accuracy depends on the subjective experience. Therefore, thesystematic evaluation cannot fulfill the structural safety. The extreme large load may inducesome cracks in the reinforced prestressed concrete (PC) bridge which would be close withoutthe large load. In this case, the traditional evaluation methods cannot detect the crack andfulfill the meet of structural condition assessment. Therefore, the rapid convenient andeconomical structural condition assessment for the bridge system is very necessary.In this thesis, the structural condition assessment methods in frequency and timedomain are studied, which have their own characteristics. A sensitivity method in this thesisare investigated and discussed. The static and dynamic tests of simply support box-sectiongirder bridge and three-span continuous box-section girder are studied to verify theproposed method. The main content includes that:1. Dynamic experiments are conducted to investigate the sensitivity of dynamic timedomain response. The structural stiffness is obtained with the sensitivity of structuraldisplacement, velocity and acceleration. The calculation iteration is used in the process ofstructural stiffness identification. The results of investigation demonstrate that the damagedetection results are more accurate with more structural response. The damage detectionresults are more accurate with the measurements of structural acceleration thandisplacement without measurement noise. The optimization method will be applied toobtain acceptable result in the structural stiffness identification for the case withmeasurement noise.2. Experimental studies with a box-section girder bridge are conduct with the proposeddamage detection method in this thesis. With the comparison of the response ofacceleration excited by the free falling of a mass from the structure the damage location andseverity could be obtained. The investigation illustrates that the proposed method can beapplied for structural damage detection. The identification result can be improved from thedifferent set of installment of the sensors with more iterative step. 3. CFL was used for the damage PC girder maintenance. The bearing capacity andstructural stiffness can be calculated with the proposed method in this thesis. The theoreticanalysis and the experimental result coincide very well. It is illustrated that the maintenanceof the box-section could improve the bearing capacity and the stiffness of the structure isreinforced. It is demonstrated that the damaged prestressed reinforce concrete can beimproved with carbon fiber laminate (CFL).4. The condition of the structure before and after structural damage was investigatedwith the first and second mode. It is demonstrated that the frequencies of first two modesdecrease apparently and the first and second mode shape become larger after the damage.While the box-section girder is reinforced, the frequencies and modal shape were nearly thesame with the damage structure. This is because the thickness of CFL is small whichcontribute to the stiffness limitedly.5. With the excitation of moving vehicle load a three continuous PC concrete reinforcebox-girder bridge was investigated for damage detection. Moving vehicle and bridgeinteraction was studied with parallel vehicles excitation. The proposed damage detection andstructural condition assessment method was validated with the above evaluation methodand the excitation and dynamic test.