| This paper was based on the background of Yueyang Dongting Lake Bridge and Researches on Key Technologies of Long-span Steel Truss Stiffening Girder in Long-span Suspension Bridge(2013318798320), which was a construction science and technology project of Ministry of Transport, summarizing existing domestic and overseas theories and experimental researches of deck-truss composite stiffening steel girder. The mechanical characteristics, continuous analysis methods, bending theory and restraint torsional calculation theory considering shear lag and shear effect of deck-truss composite stiffening steel girder were studied by applying FEA method and theoretical derivations. The study emphases and conclusions of the paper were listed as following.The mechanical behavior of composite stiffening steel girder was analyzed by applying plate-beam mixed finite element method. Transfer paths and ratios of vertical force in floor system when deck loads acting on deck-truss composite stiffening steel girder were obtained. Effects on ratios of force in different members of floor system by changing of several parameters, such as ratios of internode length and main girder width, numbers of small horizontal beam, vertical stiffness ratio of big and small horizontal beams, vertical stiffness ratio of horizontal beam and bridge deck have been studied. In the meantime, the load transfer characteristics inside floor system with different component sizes was given in form of table. Basic formula of vertical force distribution in floor system and simplified mechanical models of top chord, central longitudinal beam and transverse truss were also obtained.Based on the principle of energy, computational formula of continuous equivalent thickness for webs and bracings of main truss in deck-truss composite stiffening girder was deduced. And on the basis of this principle, continuous equivalent sections were founded. Assuming rigid rotation and same warping in the equivalent section for deck-truss composite stiffening girder, numerical integration method was applied in deducing torsional rigidity of equivalent section and equivalent shear thickness of deck stiffened by U ribs. Taking Yueyang Dongting Lake Bridge as research object, calculated values of displacement and stress were obtained with continuous analysis method and were also compared with results of the analysis of fine finite element method. The results showed that continuous analysis method was with high computational accuracy and this method remarkably improved the computing efficiency.Based on continuous analysis method for deck-truss composite stiffening girder, theoretical analysis model of shear lag effect was established. Considering differences between out-of-plane and tangential equivalent thickness of orthotropic steel deck plate, and with modified axial force equilibrium condition for stiffening girder by introducing additional warping displacement, longitudinal warping displacement, the control equation of shear lag was established for deck-truss composite stiffening steel girder. Governing differential equation of shear lag for deck-truss composite stiffening girder was deduced on the basis of the principle of energy, and shear lag computational formula was then obtained, the validity of which was verified using FEA method. Finally, referring to the definition of effective width factor applied in bridge deck, formula of effective width factor applied in static deck-truss composite stiffening girder which would be suited in designing was provided.According to the principle of energy while considering shear lag and shear effect, vertical deflection formula of deck-truss composite stiffening girder was founded, and increased degree of vertical deflection produced by shear lag and shear effect was achieved by means of calculating a static case with the same type girder. The results showed that ratio of additive deflection produced by shear achieved approximately from 30% to 50%, but that by shear lag was less than 10%. On the basis of characteristic of shear and axial force generated in deck-truss composite with stiffening girder system, formula for calculating axial force of members in main truss, K style bracing and X style bracing was established, and that was also obtained in W style transversal truss and outside web based on deck load transport mechanism.Considering the difference in the out-of-plane and tangential equivalent thickness of the orthotropic deck, the main truss and the bracing truss, this paper transformed the deck-truss composite stiffening girder equivalent to the thin-walled box girder by utilizing a continuous method, deduced equilibrium condition of shearing force in thin-walled element, and got the calculation formula of out-of-plane stress by restrained torsion and shear.This paper established the control differential equation of constrained torsion of sections of deck-truss composite stiffening girder based on the general principles of the second theory of Wu, and get the calculation formula of torsion angle θ, degree of restraint torsion β’, bi-moment of restraint torsion B and buckling torque Tω in order to solve the torsion effect of deck-truss composite stiffening girder. On the basis of the solving process of the geometrical features of thin walled beam bending and torsion, this paper deduced the calculation formula of geometrical features of thin-walled beam bending and torsion.Mechanical characteristic of bending and torsion in deck-truss composite stiffening girder of long-span suspension bridge was studied by means of continuous analysis method and plate-beam mixed fine FEA method. Under the action of moving load and transverse windward load, this paper got the deformation and strength behavior of girder and part members respectively. Deflection and strength of composite girder which was integrating deck and chord were compared to separate girder which was not integrating deck and chord. Results of deflection and strength in different structure system with deck-truss composite stiffening girder were also analyzed. |
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