Gust factors

When details are given they should be checked, if only by comparison with equivalent wind speeds derived from first principles, to ensure that they are reasonable. Depending on the specified requirements, the wind speeds may or may not utilize gust wind speeds as in CPS (3) or mean hourly wind speeds, v, with applied gust factors. 

Gust Factors for Hyperbolic Cooling Towers Singh, Mahendra P. Gupta, Ajaya K. 

Determination of Gust Factor, Gf, for Vessels Where h/D > 4 orT >1 Second... 

P = design wind pressure, PSF Ce = combined height, exposure, and gust factor. See Table 3-6. 

Combined Height, Exposure, and Gust Factor Coefficient (Ce) ... 

Fy = minimum yield stress, shell, psi P = internal pressure, psi P,. = external pressure, psi G = gust factor, wind Kz = velocity pressure coefficient 1 = importance factor, 1.0-1.25 for vessels V = basic wand speed, mph Ks = pier spring rate, 46 fl — friction coefficient y = pier deflection, in. 

For rigid structures, the gust factor may be taken as 0.85 or as calculated below ... 

In addition to the tabular data above, the following must be given to determine the gust factor, Gf ... 

Determination of design win speed, gust factor, and wind pressure coefficient is based on ANSI A 58.1. Application of ASCE Paper No. 3269 for the calculation of wind pressure coefficient of which procedure is not described in ANSI A 58.1 is acceptable. 

H. Ishizaki, Wind Profiles, Turbulence Intensities, and Gust Factors for Design in Typhoon-Prone Regions, Journal of Wind Engineering and Industrial Aerodynamics. 13., 55-66 (1983). 

In addition, it is necessary to modify Eq.a by the force coefficient Cj, which is 0.6 for a cylinder, and by the gust factor Gj for the height of the vessel above ground level. Once the basic wind speed is determined from Fig. 16.3, the velocity pressure for a cylinder is obtained from Table 16. la. To determine the... 

Table 16.1b Gust Factor for Cylinder at Various Heights...

Height above ground (ft) Gust factor Height above ground (ft) Gust factor... 

The extreme, normal (rather frequent) and frequent values for wind speed can be determined either from site monitoring data or the wind speed standards of the national building code. Data from monitoring typically cover at least 10 continuous years of annual extreme wind speed records. The type of wind speed recorded over time has to be specified (e.g. average, 10 min peak, 3 s gust, etc.) so that a proper gust factor can be defined in converting wind... 

Basic gust wind speed, V, is multiplied by a series of S factors, which adjust the basic values to design values for the particular situation. CPS uses up to four S factors ... 

We eventually reached the Pole on Day 68 of the expedition, arriving in what were becoming familiar temperatures of below -40 °C combined with winds gusting above 40 knots. The resultant windchill factor was around... 

This paper discusses the impact of wind action on natural-draft cooling towers. The structure of the wind load may be divided into a static, a quasistatic, and a resonant part. The effect of surface roughness of the shell and of wind profile on the static load is discussed. The quasistatic load may be described by the variance of the pressure fluctuations and their circumferential and meridional correlations. The high-frequency end of the pressure spectra and of the coherence functions are used for the analysis of the resonant response. It is shown that the resonant response is small even for very high towers, however, it increases linearly with wind velocity. Equivalent static loads may be defined using appropriate gust-response factors. These loads produce an approximation of the behavior of the structure and in general are accurate. 11 refs, cited. 

Certain simplifications that allow the dynamic response to be reconciled with equivalent static loadings are examined. In earthquake loading the dominant effects are found to occur in the lowest mode for which no cross sectional distortion takes place. In wind loading the dynamic response is spread over several modes. The maximum dynamic tensile stresses at the windward base of the tower can be estimated using simple gust effect factors. 20 refs, cited. 

Gy=gust response factor for flexible vessels h = height of vessel, ft I = importance factor, see Table 3-1 Iz = the intensity of turbulence at height z Kz = velocity pressure exposure coefficient from Table 3-3a, dimensionless Kct = topographic factor, use 1.0 unless vessel is located near or on isolated hills. See ASCE for specific requirements M = overturning moment at base, ft-lb Ni,Nh,Nb,Na = calculation factors... 

Davenport gives in the paper Gust Loading Factors (Davenport 1967) an approach how wind impacts can he applied to structures using velocity spectrmns. 

Davenport, A.G. (June, 1967). Gust loading factors. Journal... 

Vickery, B.J. (Nov. 1970). On the reliability of gust loading factors. Proc. of Tech. Meetg. Cone. Wind Load on Bldgs, and Struct Building Sience Series 30. 

The vertical acceleration factor for air depends on the pitch acceleration of the type of aircraft when subjected to the maximum gust conditions and the position of the cargo relative to the aircraft centre of gravity. The values shown are the maxima for most modem aircraft. The 9g forward longitudinal factor is required when there is no reinforced bulkhead between the cargo space and the aircraft crew. 

Dynamic Analysis. Dynamic Analysis (Modal Analysis) was completed to determine the fundamental natural frequencies and corresponding modal shapes of the A-frame structure. Natural frequencies were calculated to be 0.6 ( ) Hz (pin-ended) and 0.8 ( ) Hz (fixed-ended) in line with the ropes, and 0.8 ( ) Hz (pin-ended) and 1.0 ( ) (fixed-ended) perpendicular to the ropes. The natural frequencies were used to determine the wind gust load factor (Cg), examine the NBCC (2010) requirements for earthquake design, and check for possible vibrations that could be initiated by the frequency of rotating equipment corresponding the primary natural frequencies of the structure. 

G = gust effect factor Gf = gust response factor for flexible vessels... 

Operating Basis 64.82m/sec (145mph) (3 second gust) importance factor 1.15 (safety), 1.0 (non-safety) exposure C topographic factor 1.0... 

Ce = coefficient for combined height, exposure, and gust Cq = pressure factor = 0.8 for cylinders Qf = wind stagnation pressure at 30-ft level / = importance factor =1.0 for pressure vessel... 

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