Mei X.-D.,Bridge Science Research Institute LTD |
Mei X.-D.,Key Laboratory of Bridge Structure Safety and Health of Hubei Province |
Li Y.-M.,The 1st Engineering Co. |
Li Z.,The 1st Engineering Co.
Bridge Construction | Year: 2013
To provide solution to the problem of influence from tensioning of the prestressing strands for simply-supported girder and to the optimization of removal of the temporary suspenders and pre-raising amount of the inclination angle of the first segment in the process of span-by-span assembling and erection of precast segments of the prestressed concrete girder bridge, the north approach bridge of Taohuayu Huanghe River Bridge in Zhengzhou on the inner side of the river dyke was cited as an example. The forces of the suspending system formed by the overhead launching gantry, temporary suspenders and concrete main girder for assembling and erection of the precast segments of the bridge were analyzed, using the simplified finite element model that could fulfill rapid calculation and could produce reliable calculation results. The results of the analysis indicate that the tensioning of the prestressing strands for simply-supported girder can cause the main girder to camber inversely and make the force distribution of the temporary suspenders become dramatically worsen, the forces of the midspan suspenders reduced and the forces of the suspenders nearby the girder ends increased. The optimal sequence of removal of the temporary suspenders for system transformation is that the removal should proceed symmetrically from the midspan towards the ends of the girder. Most of the suspenders can be removed in one time while the rest of the suspenders need to relaxed first before removal. The pre-raising amount of the inclination angle of the first segment of the bridge to be constructed by the suspending and assembling technology is 13.6 mm/3.84 m.
Huang Q.,Bridge Science Research Institute LTD |
Huang Q.,Key Laboratory of Bridge Structure Safety and Health of Hubei Province
Bridge Construction | Year: 2014
In regard of the situation of the bridge structure safety imperiled by the load stacked nearby the bridge piers in violation of the regulations, the influences of the ground stacked load on the existing bridge structure were studied. A ramp bridge was taken as an example and several indices including the displacement of the girder, pier tops and bearings and the gap changing of the expansion joint of the bridge were continuously monitored. The displacement of the structure was judged to be stable or not at the time the dangerous situation occurred. The American geotechnical software FLAC3D was used to simulate the spatial deformation and force conditions of the passive piles and the ground stacked load was verified to be the major factor causing the displacement of the piers. The influences of the stacked load on the pile foundations and superstructure of the bridge were theoretically analyzed and the pile foundations were tested by the two-velocity method. The results of the study show that under the action of the ground stacked load, the piers will horizontally displace and will further cause the bearings at the pier tops to displace and the concrete at the junction of the piles and pile cap to crack. It is therefore proposed that the displacement of the ramp bridge structure should be continuously monitored and at the same time, the girder should be restored to its designed position right away and the substructure should be repaired and strengthened. ©, 2014, Bridge Construction. All right reserved.
Cui Q.-Q.,Bridge Science Research Institute LTD |
Cui Q.-Q.,Key Laboratory of Bridge Structure Safety and Health of Hubei Province
Bridge Construction | Year: 2014
Nowadays, the substructures of the major bridges crossing the rivers have been commonly constructed by the steel cofferdams. The cofferdams resist the water buoyant forces and other loads, mainly relaying on the bonding forces between the cofferdam base sealing concrete and the steel pipe piles. To study the major factors having influences on the bonding forces and to obtain the reliable values of the forces, 4 groups of 9 models for the bonding forces were prepared. In the models, the hollow steel pipes were used to simulate the steel pipe piles and the base sealing concrete at the lower parts of the models was cast according to the construction technology actually used in the field. At the upper parts of the steel pipe piles in the models, the reverse brackets were arranged and together with the base sealing concrete at the lower parts, the self-balanced loading systems were formed. At the middle parts of the pipe piles, the jacks were used to generate forces and to simulate the actual force conditions of the cofferdams, the model tests were carried out by applying load in steps and the simulation calculation and analysis were made as well. The results of the tests show that the bonding forces of the C25 base sealing concrete is 0.3~0.54 MPa and the empirical values of the forces having been used in the current design are a bit too safe. The greater the concrete strength is, the greater the bonding forces will be. The ratios of the base sealing concrete depth and the steel pipe pile diameters do not have significant influences on the bonding forces while the construction technology and the steel pipe pile surface status can have considerable influences on the forces. ©, 2014, Wuhan Bridge Research Institute. All right reserved.
Zhang Q.-Z.,Bridge Science Research Institute LTD |
Zhang Q.-Z.,Key Laboratory of Bridge Structure Safety and Health of Hubei Province |
Wu B.-S.,Jiangxi Provincial Transport Design and Research Institute
Bridge Construction | Year: 2013
To study the force condition characteristics of the steel and concrete joint section of Jiujiang Changjiang River Highway Bridge, the physical model on a large scale of 1:2 for the joint section with steel cells and rear bearing plates of the bridge was fabricated, tested and the force conditions of the steel structure, concrete box girder, steel cells, U ribs and PBL shear studs and relative slip of the joint surfaces of the steel and concrete of the joint section under the maximum normal bending moment were analyzed. The results of the test and analysis show that the stress of the steel and concrete joint section presents a smooth decrease from the steel girder stiffening section, joint section to the concrete stiffening transition section. The measured maximum compressive stress of the steel structure appears in the bottom plate U ribs, the measured maximum compressive stress of the concrete appears in the top slab with the smallest sectional area and the maximum tensile stress appears inside the bottom plate steel cells. The stress of the shear studs becomes gradually decreased from the locations far from the bearing plates towards the plates, the forces of the webs of the steel cells and the relative slip between the steel and concrete are very little and the measured maximum stress of various parts of the joint section does not exceed the allowable stress values as specified in the codes.
Cheng H.,Key Laboratory of Bridge Structure Safety and Health of Hubei Province |
Cheng H.,China Railway Bridge Science Research Institute Ltd.
Bridge Construction | Year: 2015
The Huanghe River Bridge herewith is a 3-span prestressed concrete continuous rigid-frame bridge with span arrangement (96+132+96) m and is located on the Newly-Built Second Line of Datong-Zhungeer Railway (a heavy haul railway), Shenhua Group. Owing to the need of increasing the transportation capacity of the line, the speeds of the trains C80B and KM70 traveling on the line were to be raised from 60 km/h to about 80 km/h. To evaluate the adaptability of the Huanghe River Bridge after the speeds of the trains were raised, the fiber grating stress sensors and deflection and vibration sensors were respectively used to monitor the stress, deflection and vibration responses of the bridge in the process of the train marshalling and train speed raising. The stress, deflection and vibration responses of the bridge as well as the train critical speeds when the vertical resonance occurred in the bridge were analyzed. The results of the analysis reveal that when the train KM70 passes through the bridge at the speed of 74 km/h, the train excitation frequencies are close to the vertical load frequencies of the train-bridge coupling system, the deflection changing amplitude and stress amplitude of the bridge are great and the dynamic coefficients exceed the values as specified in the codes, from which the occurrence of the vertical resonance in the bridge can be judged. It is hence proposed that the vibration mitigation for the bridge should be handled in the situation that the speed of the train KM70 is not raised or before the speed of the train is raised and the deep-going analysis of the vertical resonance of the bridge should be implemented, using the train-bridge coupling method. ©, 2015, Wuhan Bridge Research Institute. All right reserved.