Determining Of Reasonable Construction States And Construction Controlling Of Hybrid Beam Cable-stayed Bridge With High And Low Towers

Hybrid girder cable-stayed bridge has a good mechanical performance and lowereconomic cost compared to other types of the same span bridge,meanwhile,the side concretebeam and the main tower can be constructed at the same time.Because of that,the constructionperiod can be greatly shorten.In addition to have the advantages of the hybrid girdercable-stayed bridge,the high and low tower cable-stayed bridge due to the two asymmetrymain tower,so it obtains reasonable and more economical bridge layout in specialhydrological, geological and topographical conditions,also the reasonable combination of thehigh and low tower can avoid it to be constructed in the deepwater foundation as well as tomeet the requirements of the midspan navigation. The hybrid beam cable-stayed bridge withhigh and low towers will become one of the important direction for the future development oflarge span cable-stayed bridge.The two main beam is inconsistent due to the high degree asymmetry of the main towerin the hybrid cable-stayed bridge with high and low tower, which cause the big stiffnessdifference of the main beam during the construction. Compare to conventional cable-stayedbridge with symmetric structure, it resulted in increasing the difficulty in determining thereasonable construction state calculation as well as the construction control. With thebackground of Huangyi Yangtze river bridge in this paper, in connection with the practicalproblems encountered in the pre-modeling calculations and construction control process,several aspects are studying as the following:(1) The determination of the reasonable construction state of hybrid grider cable-stayedbridge with high and low towers.First, aim at the construction features of the Huangyi Yangtze river bridge steel boxgirder and the existing problems, optimizing and adjustmenting the constructionprocess.Secondly, considering the restrict of the construction-stage cable force which iscaused by the particularity asymmetry structural of the hybrid beam with high and lowtowers,proposing a comprehensive scheme that use the result from the backward analysismethod for forward trial for determining the reasonable construction-stage cable. It caneffectively solves the problem that the two main beam elevation alignment difficulty at thetime of closure due to the inconsistent length of the two main beam during the constructionprocess. Lastly, discuss and analysis the determining of middle-state cable foere andpositioning elevation of the main beam. (2) The calculation of stress-free fabrication geometry and the stress-free cable length.Based on the overall construction control mind, do a research on the calculation ofstress-free fabrication geometry and the stress-free cable length. Using the results from theexisting finite element construction model, by the method of calculating the stress-free anglebetween the two steel box girder, the stress-free fabrication geometry and other relevant sizescan be easily obtain.Analysis the shortcomings of the existing method in calculating the stress-free cablelength.Proposing a practical iterative method based on the catenary theory which use thehorizontal force in the tower as the control objectives. This method has the advantages of fastconvergence speed high accuracy and simple calculation features and convenient to use in theactual project. Proposeing the concept of the reasonable blanking cable length according tothe characteristics for cable several times tension, this can effectively ensure the nut anchoreffectivly anchor on the cup during the overall construction progress.(3)Error adjustment during the construction based on the geometry controlling method.Use the temporary load error during the construction of Huangyi yangtze river bridge asa example,analysis the shortcomings that the traditional error adjusting method which withthe control target of hanger cable force may cause the deviation of cable length that affect thenormal construction. A new method is propose in this paper that adjusting the error with thecontrol target of stress-free cable length.It can not only effectively eliminate the influence forinternal forces cause by parameter error but also balance the length of the cable which ensurethe normal construction, it has great practical significance in longspan cable-stayed bridgeconstruction control.(4) Structural behavior prediction during the construction of hybrid beam cable-stayedbridge with high and low towers.Discussing the principle and method of gray theory and BP neural network theoryseparately in the structural behavior prediction during the construction control. Analysis theapplicable conditions of the two methods, programming two different structural behaviorprediction models using matlab that applicated different construction conditions and comparethe prediction results with actual measurement results.It proves the availability of the twomethods in construction contrlo of longspan cable-stayed bridge.Finally, aim at theshortcomings of the gray theory and BP neural network theory, proposing a method whichcomplementary combines the advantages of two theory called grey neural network model anduse it in the practical construction constrol.