hdn32
Structural
- Sep 28, 2004
- 51
Dear Eng-tips forum users,
I am currently asked to work on a 35ft (high) missile barrier/fence and about 34.5ft in width.
The prelim layout has called for 5 equally spaced posts (4 x 8.88’ spacing) and metal mesh with 52% of open area is proposed. The metal mesh would run from about 6 inches of the base to the top of the 35’ pole. Also, there are horizontal members that span between posts to transfer loads from the metal mesh to the pole.
There are a few issues that I have run into while working on this structure as followings:
- Wind load calculation:
+ Fundamental frequency: I tried ASCE 7-05 Eq. C6-22a (p 294) for a prelim HSS 8x6x0.25 section, but the result seems to be too low (= 0.126). Could anyone point me to any different formula/method so that I can double check the about number?
+ Damping ratio: What would be reasonable values to use?
- Ice load calculation: I used the ASCE 7-05 Eq. 10-2 (p100) with a multiplier of 0.8 for vertical plate and the ice volume seems to be high. The commentary of ASCE 7 does not say much about ice loading. Has anyone run into this equation and thought about it already? Please share with me.
- Deflection limit: Somehow a limit of h/50 with unfactored wind load pop-up in mind my, but I could not recall where I saw it. Could anyone help me?
- Consideration for slenderness: AISC user’s note recommends keeping the kl/r not to exceed 200 for compression member. In the past, I have ignored this suggestion when dealing with secondary/redundant bracing member in transmission/telecom towers. What would you say about the recommendation for fence/barrier structures?
I would appreciate very much for any comment/suggestion.
Sincerely,
Hdn32
I am currently asked to work on a 35ft (high) missile barrier/fence and about 34.5ft in width.
The prelim layout has called for 5 equally spaced posts (4 x 8.88’ spacing) and metal mesh with 52% of open area is proposed. The metal mesh would run from about 6 inches of the base to the top of the 35’ pole. Also, there are horizontal members that span between posts to transfer loads from the metal mesh to the pole.
There are a few issues that I have run into while working on this structure as followings:
- Wind load calculation:
+ Fundamental frequency: I tried ASCE 7-05 Eq. C6-22a (p 294) for a prelim HSS 8x6x0.25 section, but the result seems to be too low (= 0.126). Could anyone point me to any different formula/method so that I can double check the about number?
+ Damping ratio: What would be reasonable values to use?
- Ice load calculation: I used the ASCE 7-05 Eq. 10-2 (p100) with a multiplier of 0.8 for vertical plate and the ice volume seems to be high. The commentary of ASCE 7 does not say much about ice loading. Has anyone run into this equation and thought about it already? Please share with me.
- Deflection limit: Somehow a limit of h/50 with unfactored wind load pop-up in mind my, but I could not recall where I saw it. Could anyone help me?
- Consideration for slenderness: AISC user’s note recommends keeping the kl/r not to exceed 200 for compression member. In the past, I have ignored this suggestion when dealing with secondary/redundant bracing member in transmission/telecom towers. What would you say about the recommendation for fence/barrier structures?
I would appreciate very much for any comment/suggestion.
Sincerely,
Hdn32