In tower design, the basic load is increased by the use of an overload factor and the tower is designed to stresses approaching failures in yielding and buckling. The ASCE “Guide for Design of Steel Transmission Towers” (1971) states in the introduction that “One of the many ways in which tower design differs from bridge and building design is that tower design uses overload factors to incorporate factors of safety in place of reducing allowable stress. The influence of the design of steel transmission towers was a motivating force in this concept.
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The code first specified Overload Capacity Factors for steel in the Sixth edition and then specified them for most of the other materials in 1977.
The NESC originally addressed reliability by providing allowable stress design of wood, steel and concrete structures. PICCIANO, in Probabilistic Methods Applied to Electric Power Systems, 1987 THE RESPONSE TO LOADS Overall, the three suggested safety factors are reasonable and can be used in the safety evaluation of high arch dams.į.G. From the failure behavior, the ultimate bearing capacity mainly depends on the middle–up arch structure.
However, the ultimate safety factor k 3 is not substantially improved because the strengthening effect of the support dam is mainly at the middle–down region of the old arch dam while the bearing capacity of the middle–up arches has not been improved significantly. The improvement of the structural mutation safety factor k 2 after strengthening shows that the treatment measures implemented for the arch dam are effective. When Kölnbrein is in good working condition after the strengthening, the calculated curtain safety factor k 1 improves to 1.2. When the grouting curtain was broken before strengthening, the calculated curtain safety factor k 1 was 0.9. Relational curves between the stream displacement of the dam crest and the overload factor.įrom the discussion, one may conclude that the curtain safety factor k 1 is a good description of the dam heel crack.
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