Identification of minimum cross-section-al dimension of main girders ensuring safety against static and dynamic instabilities in long-span cable-stayed bridges

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The followings are main results obtained from this research.1)Due to plastic elongation of cables, the girder subjected to large axial force buckles and it leads immediately to the collapse of the bridge.2)The safety factor of the cable can be reduced from conventional value of 2.5 to 2.2, which ensures the safety factor of 1.7 against the collapse of the bridge.3)On identifying ultimate strength of cable-stayed bridges, the proof stress of the cable plays an important role.4)The critical wind velocities when the lateral torsional buckling and flutter instabilities occur are not affected by the safety factor of the cable.5)The maximum span-to-width ratio from 50 to 55 can be used. The widely-believed maximum ratio of40 is not critical one.6)From in-plane instability viewpoint, considerably low depth of the girder may be used (eg. span/1000). However, from viewpoints of fabrication, erection and maintenance, the minimum value from 2.0 to 2.5 meters is recommended.7)The minimum ratio among cable proof stress-to-produced stress ratio, local buckling strength-to-produced stress ratio in the girder and tower will give a minimum load factor at ultimate state of the cable-stayed bridges.