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Wind Load directions and amplification factors.

Wind Load directions and amplification factors.

Wind Load directions and amplification factors.

In ASCE 7-10,2.3.2 are given the basic combinations for strength design:
1. 1.4D
2. 1.2D + 1.6L + 0.5(Lr or S or R)
3. 1.2D + 1.6(Lr or S or R) + (L or 0.5W)
4. 1.2D + 1.0W + L + 0.5(Lr or S or R)
5. 1.2D + 1.0E + L + 0.2S
6. 0.9D + 1.0W
7. 0.9D + 1.0E

In equation 4 and 6 , W refers to wind,and in 5 and 7, E refer to the earthquack load.
My questions are:
1-is there any redundancy/overstrength factor to multiply wind loads(obtained by manual calculation or by software) with to obtain W? I mean to obtain the seismic load Eh we had to multiply QE(load obtained by seismic analysis) by a redundancy/overstrength factor.Is this a similar case? or W=wind loads obtained by applying wind pressure.
2-what are the directions of the wind that we should consider in the load combinations?I mean 2 orthogonal directions are sufficient?
3-For seismic loads ASCE 7-10,12.5 for each seismic design category gives a method of combining load effect obtained from applying seismic load in each direction.Is there a similar thing for wind? or the wind cases obtained for each direction are sufficient?
Thank u.

RE: Wind Load directions and amplification factors.

1. Redundancy and Overstrength do not apply to wind loads. My (poor) understanding is that this is because structures are designed to resist wind entirely within the elastic range, while seismic design allows for some use of plasticity and ductility.

2. Depending on your structure, directions other than your two orthogonal grid directions may govern. Check out the Citicorp building case study for an example.

3. I'll leave a definitive answer here for others. I know AASHTO has provisions for wind at different skew angles and combined in multiple directions.

The name is a long story -- just call me Lo.

RE: Wind Load directions and amplification factors.

1. No, these do not apply to ASCE 7 wind loads.
2. See Figure 27.4-8 for considering wind directions. You are also free to add more.
3. See 2. There is no requirement for wind loads corresponding to seismic orthogonality combinations.

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