| In civil engineering, bridge is a structure providing passage over an obstaclewithout closing the way beneath. To most members of the public, bridges are a fixedobject-solid as a granite mountainside. As the engineering community well aware,bridges are unlike any other structure. They expand and contract greatly in heat or coldweathers, and they shiver with the wind and subjected to abuse in the form of road sal t,corrosion, and overloading. A bridge is the most important part of transportation systemand it is important for everyone. The conception, development and worldwideconstruction of bridges represents the most interesting and important achievements incivil engineering. The bridge structure consists of two parts: the first part is known assuperstructure system which is composed of bearings, girders or beams, deck, joints,pavement layers, security barrier, and drainage system. Whereas, the second part isknown as substructure system which includes the foundations, piers, and piers caps.The objectives of this research are to analyze the designed internal forces under deadand live loads before strengthening and repairing of damaged structural members o f thebridges structure by adopting theoretical analysis of static and dynamic performance ofthe bridges structure, to inspect and identify the damages in structural members of thebridges structure, to evaluate the static and dynamic performance of the bridges structureby adopting static and dynamic load tests, to improve the structural performance ofdamaged members of the bridges structure by using different strengthening and repairingmethods, and to evaluate the structural performance after strengthening and repairing byusing theoretical and experimental analysis of static and dynamic responses.According to the types of damages and designs, three bridges structures are selectedin this study. The first bridge is known as Jiamusi prestressed concrete box gider withprecast T-beams bridge, the second bridge is known as Hashaung prestressed box girderskewed bridge, and the third bridge is known as Sanguxian prestressed segmental boxgirder bridge. The theoretical analysis of designed internal forces of the bridges structureis adopted by using SAP2000Ver.14.2.0software. Static and dynamic analysis is carriedout to determine the structural responses of the selected bridges structure. The results ofanalysis show that the maximum values of strains, stresses, and vertical deflections forall the bridges structure meet the allowable limit values in Chinese codes, except thereare tensile stresses which are more than the allowable values in the codes, leading toappear the cracks in the locations which have high tensile stresses, because of theoriginal design of the bridges structure according to Chinese code JTJ023-85and thedesign loads are less than the design loads in Chinese code JTG D62-04and dose notmeet the overloading traffic loads on the bridges. The dynamic responses such as naturalfrequency, vibration frequency, acceleration, displacement, velocity, and impact factor are determined for each bridge structure. The results of dynamic analysis show that thespeeds of vehicles have significant effects on the dynamic responses. For Jiamusi bridge,the average vibration frequency of the bridge structure is more than the naturalfrequency, indicating that the bridge structure suffers from vibration state. For Hashuangbridge, the average value of vibration frequency of the bridge structure is less than thenatural frequency, indicating that the vibration state of the bridge structure in good state.For Sanguxian bridge, the average value of vibration frequency of the bridge structure isless than the value of natural frequency, indicating that the vibration state of the bridgein good state.The results of damage inspection of the bridges structure show that the structuralmembers of the bridges structure suffere from many damages and these damages areranged from simple to serious. There are many cracks which they are appeared in thedifferent locations of the box girders of the bridges structure which are affected thestructural performance of the bridges structure, causing to decrease the stiffness andelastic working state. Field tests during inspection process are adopted to evaluate theproperties of materials such as the depth of concrete carbonation test, compressivestrength of concrete test, level of bridge deck test, and the corrosion of steelreinforcement test. Static and dynamic load test are adopted to evaluate the structuralperformance of the bridges structures. According to the evaluation factors in Chinesecodes, the evaluation process shown that the most structural members of the bridgestructures have not enough stiffness and bearing capacity, and the elastic working statewas not good. Therefore, the bridges structures need to repair and strengthen to improvethe structural performance and to extend the service life of the bridges structures.There are different methods of repairing and strengthening which are used toimprove the static and dynamic structural performance of the bridges structures. ForJiamusi bridge, the repairing and strengthening methods of the bridge structure includesrepairing the bridge deck pavement, replacement of all the expansion joints, treating thebearing, application of chemical grouting method for treating the cracks, strengtheningthe top floor of box girders by using steel plates, and strengthening the main span of T-shape cantilever structure by using external pre-stressing tendons. For Hashuang bridge,the repairing and strengthening methods includes the treatment of the cracks, thickeningthe web of box girder along the bridge length and adding internal pre-stressing tendonsin the thickening web, and constructed reinforced concrete cross beams (diaphragms)between two box girders of the bridge structure. The methods of repairing andstrengthening of Sanguxian bridge includes reconstruction of the deck of the bridge bycasting10cm layer, strengthening the web and bottom floor of box girders of middlespans and side spans by sticking the steel plates, strengthening the whole bridgestructure by using external pre-stressing tendons, strengthening the lower edge of bottom closure segment of middle span by using high strength composite fiber, and treatmentthe cracks.Theoretical analysis of static and dynamic structural responses of the bridgesstructures after repairing and strengthening are adopted by using SAP2000Ver.14.2.0software. The results of theoretical analysis of static structural response shown that thevalues of tensile stresses are decreased about50%, and the values of vertical deflectionare decreased comparing with the values before strengthening, indicating that thestrengthening methods are effective to improve the structural performance of the bridgesstructures. From the results of theoretical analysis of dynamic structural responses it canbe shown that the values of natural frequency are increased comparing with the valuesbefore strengthening, indicating that the strengthening methods are effective to reducethe vibration and to improve the elasticity of the bridges structures. Damage inspection,static and dynamic load tests are adopted for the bridges structures after repairing andstrengthening. The results of damage inspection of the bridges structural parts show thatthe state of structural members is good. There are not new cracks in the grouting area,indicating that the quality of cracks grouting in good state. The quality of pasting steelplates is in good state. All expansion joints are replaced but some of the expansion jointsare still damaged in serious degree after using the bridges. Therefore, the expansion jointloss the function of the expansion, which is influenced the performance of the bridgesstructure, but most of them in good state. The external pre-stressing systems of thestrengthening bridges are in good state. The state of the bridges decks system is in goodstate but there are some places have cracks and bleeding of asphalt on Jiamusi bridge.The results of static load tests of the bridges structure show that the tested values ofstatic structural response are less than the theoretical values, indicating that thestructural strength of the bridge structure meet the design requirements and the state ofelastic working state is good, but Hashuang bridge has just dynamic load test. Theresults of dynamic load tests analysis after repairing and strengthening processes ofbridges structures show that the values of measured natural frequencies are increasedand vibration frequencies are decreased. Therefore, the repairing and strengtheningmethods are effective to improve the static and dynamic structural performance ofbridges structure. According to the desing and construction methods of the three bridgesstructure, Jiamusi bridge appeared maximum values of vertical deflection and dynamicacceleration and Hashuang appeared maximu values of tensile stress and naturalfrequency. |
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