Gust-Effect Factor G (ASCE 7 §26.11)

The ASCE 7 gust-effect factor G for a rigid building, instead of the flat 0.85 default.

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Example

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Details, formula, and sources

ASCE 7 §26.11.4 rigid form G = 0.925 (1 + 1.7 gQ Iz Q)/(1 + 1.7 gv Iz), gQ = gv = 3.4, with Iz = c (33/zbar)^(1/6), Lz = l (zbar/33)^eps, Q = sqrt(1/(1 + 0.63 ((B+h)/Lz)^0.63)), zbar = max(0.6h, zmin), and the Table 26.11-1 exposure constants. A 30 ft tall, 100 ft wide building in Exposure C gives G 0.86 (the 0.85 default is slightly unconservative); a taller, narrower building or a smoother exposure raises it. Rigid buildings only; a flexible building needs Gf with the resonant response R. The engineer of record governs.

G = 0.925 (1 + 1.7 gQ Iz Q)/(1 + 1.7 gv Iz), gQ = gv = 3.4; Iz = c (33/zbar)^(1/6); Lz = l (zbar/33)^eps; Q = sqrt(1/(1 + 0.63 ((B+h)/Lz)^0.63)); zbar = max(0.6h, zmin).

The ASCE 7 §26.11.4 rigid-building gust-effect factor G, with the Table 26.11-1 terrain exposure constants (c, l, eps, zmin), by name.

ASCE 7 is available through the ASCE Library at ascelibrary.org; the §26.11 gust-effect-factor provisions and the Table 26.11-1 exposure constants are public. B and h are the user's own building dimensions.

Estimate. AHJ and licensed professional govern.

Field names used by the API: exposure, h_ft, b_ft, g_factor, iz, q, lz_ft

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