Renewal Research, Design, And Application Of Suspension Bridges Stiffened By Slab Girders

This dissertation firstly reviews and summarizes the basic theory of suspension bridges and the structural type evolvement of stiffening girders and the design genres, and then emphasizes to develop renewal researches into the wind-resistant stability and engineering measures of slab stiffening girder with reference to the wind induced collapse of the Tacoma Old Bridge. The results of the theoretical analysis are applied to the design of suspension bridges stiffened by prestressed slab or steel slab girders, then a serious of theoretical analysis and wind tunnel tests are undertaken to detect the issue of wind-resistant stability and engineering design measures one by one. As a result, the conclusions are drawn on appropriate span lengths and application conditions corresponding to different girder types.The conclusion is: owning to the sufficient wind-resistant capacity resulting from its good ventilating capacity and large stiffness, the truss stiffening girder satisfies the wind resistant criteria and can be applied to suspension bridges with extra-long span; for suspension bridges stiffened by box girders, the wind-resistant capacity of most bridges show no margin according to the wind-resistant criteria, the selection ofaerodynamic outline, width and span length of their stiffening girder section should be paid much attention in design; for a slab girder suspension bridge, due to its relatively smaller torsional stiffness, a more deliberate attention should be paid to the wind-resistant test, and necessary anti-wind measures should be applied.In engineering design, the appropriate span length varies for different stiffening girder.There are successful applications for truss girder suspension bridges with span lengths ranging between 200-2000m due to their wide applicability.The steel box girder suspension bridges have betterapplicability with a span length ranging between 500m—1500m,and more attention should be paid to the wind stability for bridges with longer spans.Considering the rational force condition, safety, and the general economy issue of the structure, steel slab girder suspension bridges with span lengths between 200m-400m are competitive. It is verified by wind resistant theoretical analysis and wind tunnel test that the wind stability of the concrete slab girders meets the design criteria owing to their small girder depths and large self- weights.Steel slab girder suspension bridges have definite technical advantages when choosing a span length between 200m - 500m, but necessary wind-resistant measures should be appliedcorresponding to the local wind environments. Theoretical analysis and wind tunnel model test indicate that center stays are functional for the dynamic prosperities and wind stability of suspension bridges with medium and small span: The natural flexural to torsional frequency ratio is improved by 29%, and the critical flutter wind velocity improved by 20%. The center stays will be less effective with the increasing of span lengths.Limitations of slab stiffening suspension should be noticed in design application: On one hand, because of the weaker torsional stiffness of the slab girder, the wind blocking area should be reduced by lowering the girder depth to gain essential wind-resistant safety, on the other hand, this kind of bridge is usually chosen for comparatively narrower bridge carrying 2-4 carriageways (twin girders can be proposed if wider decks are required), its smaller vertical live load is favorable for application of slab girder. In addition, smaller hanger distance should be proposed to reduce the height of transversal beams or to employ a complete slab structure, it can reduce the wind blocking area and is favorable for the wind stability of the structure, but special attention should be paid under atrocious wind condition.The innovative features of this paper are as following:1. The applicable scope and application restraints of different stiffening girders of suspension bridges are studied and summarized;2. It is the first time that the renewal application of a...