Wind Velocity Ebooks Catalog
(1)P The reference wind velocity, vref, is defined as the 10 min mean wind velocity at 10 m above ground of terrain category II (see Table 8.1) having an annual probability of exceedence of 0,02 (commonly referred to as having a mean return period of 50 years). vref 0 basic value o the reference wind velocity as given in annex A a reduction of the reference wind velocity may be allowed depending upon
Aeroelastic and structural dynamic phenomena can result in dangerous static and dynamic deformations and instabilities and, thus, have very important practical consequences in many areas of technology. Especially when one is concerned with the design of modern aircraft and space vehicles, both of which are characterized by the demand for extremely lightweight structures, the solution of many structural dynamics and aeroelasticity problems is a basic requirement for achieving an operationally reliable and structurally optimal system. Aeroelastic phenomena can also play an important role in turbomachinery, civil engineering structures, wind energy converters, and even in the sound generation of musical instruments.
It shouid be noted that the map wind speeds are identical to those in BS 6399 Part 2 despite the fact that the values are 10 mm averages as opposed to hourly mean values in the British Standard. This is due to the rougher terrain used as the standard category in ENV 1991-2-4 (z0 0.05) compared with that in BS 6399 Part 2 (z0 0.03). To account for sites which are located close to the transition between two (or more) terrain categories, a transition coefficient cx Or) is introduced appropriate to a site x km from the edge of a category change. The wind characteristics do not change abruptly at a ciiange of roughness. Rather, the wind velocity adjusts gradually to the new roughness in a transition zone which grows upwards from the ground, as shown by figure B. la). Within the transition zone the wind speed is given by multiplying the value for the new roughness by the transition factor, cx(.r). Downwind of the transition zone the wind speed has adjusted to the new roughness and...
Accelerated wind speeds occur close to the base of buildings which are significantly taller than the displacement height. When considering low-rise buildings which are close to other tall buildings the rules for effective height will not necessarily lead to conservative values and specialist advice should be ENV 1991-24 provides a method for deriving directional wind speeds through the operation of the direction factor, cdlR on the reference wind velocity, iYet in 7.2. In addition, the site exposure and the influence of topography may differ by wind direction, leading to different values by direction of the roughness coefficient, cn and the topography coefficient, ct, in 8.4. However, the external pressure coefficients for buildings are given in 10.2 'for orthogonal wind directions 0 , 90 , 180 , but represent the highest values obtained in a range of wind direction
(1)P The topography coefficient, q(z), accounts for the increase of mean wind speed over isolated hills and escarpments (not undulating and mountainous regions) It is related to the wind velocity at the base of the hili or escarpment It shall be considered for locations closer than half the length of the hill slope from the crest or care should be taken to account for any increase of wind speed caused by funnelling.
Drafts of European documents for climatic actions due to temperature 8 , snow 9 and wind 10 indicate possible reduction of characteristic values Qk for temperature, snow load and wind speed in case of shorter reference (return) period (for example 5 years) than 50 years considered in normal cases. Such a reduction may be applied in transient design situations (for example during execution). (c) In accordance with EN 1991-1-4 10 the basic wind speed vb,n having the return period n years may be assessed using semi-empirical expressions where vb,50 is the basic wind velocity for 50-year return period and vb,n for n-year return period and p denotes here the probability of vb,n being exceeded corresponding to n years of return period. The constant K in equation (18) follows from Gumbel distribution as K Vv-v n, where Vv denotes coefficient of variation of annual wind speed. An approximate value K 0,2 (which corresponds to the coefficient of variation Vv 0,26) is used in the following...
(18) The relevant wind parameters (the basic value of the reference wind velocity and various factors and parameters) shall be provided in the form of maps or otherwise (see annex A) by the Relevant Authority. The value of the reference wind velocity shall conform with the definitions given in ENV 1991-1 clause 4.2
When considering combinations of railway traffic actions with wind action the maximum wind force compatible with railway traffic should also be considered. This force Fw is associated with a wind speed at the level of the deck. Note The wind speed to be considered shall be defined by the relevant authority.
(3) For hoisting or launching operations or other construction stages lasting only a few hours, the project specification should define the maximum wind velocity to be considered in the design. Unless otherwise specified, this wind velocity should not be less than 20 m s at any height. (4) Where relevant, the critical wind velocity should be determined for cross wind vibrations, galloping and flutter to ensure that these phenomena will not govern the design during the execution stages.
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