Slide 15 of 23
Notes:
“Gust effect factor" or GEF is an increasing function of speed. In addition, most structures will experience yielding as a "pushover" loading is increased, resulting in a reduced natural frequency f0 and therefore even higher load factor. This effect is the opposite of structural inelastic response to earthquakes, where the reduction in frequency leads to reduced seismic load.
This slide illustrates the difficulty encountered in using a fixed load factor to address reliability. Current design uses a load factor of 1.5 with an implicit directionality reduction to 1.3. The static curve develops a 500-year return period at a 1.5 load factor. The dynamic curves , using the same load factor, produce return periods of 175-250 years instead of 500 years,depending on damping.
