Temporary reduction of wind load

[hchiutx]

Guys,

I am in the business of designing movable equipment similar to giant cranes. I am looking for a code that allows the temporary reduction of wind load design during transient conditions. For me, my transient condition is less than 5 minutes. Both before and after the transient I will extend outriggers and will be able to withstand at least 100km/h plus LRFD safety factor. But many times during the day I have the need to retract, move for 5 minutes or less to a new site, extend again.

Does anyone have any idea of a Canadian or US code that allows temporary reduction to say, 50% of wind load during those 5 minutes? I found a German DIN standard 1055-4 that allows 50% reduction for transient condition up to 3 days. But that's German.

Thanks!

 

[JAE]

I believe that ASCE has a document for loads required during construction - check out their website and you'll probably find it.

 

[hchiutx]

Thanks! Any Canadian structural guys out there too? This monster is also used in Canada...

 

[boo1]

"Chapter 3 covers "Design Consideration". Starting on page 3-4 there is a discussion of allowable horizontal construction loads (from any source, wind included). This manual limits allowable horizontal forces to 2% of total dead load. Ways to back-figure the allowable wind speed are discussed." link and quote from SlideRuleEra
<

http://www.dot.ca.gov/hq/esc/construction/Manuals/Falsework/Falsework.htm>

ASCE's "Design Loads on Structures During Construction, SEI/ASCE 37-02".

<

https://www.asce.org/bookstore/book.cfm?book=4242>

 

[SlideRuleEra]

Here is a Babcock & Wilcox technical paper that specifically addresses construction loading for heavy-lift cranes (see page 5). Their recommendation explains and limits wind speed to 20 MPH (plus a small contingency factor). Here is the link

http://www.babcock.com/pgg/tt/pdf/BR-1670.pdf

I realize this is not exactly a regulatory code that you are looking for, but B&W is well qualified to speak on this issue. Raising a steam drum at an electric power station can take several days.

boo1 - Thanks for bringing up the California Falsework Manual reference, I had forgotten about that one.

http://www.SlideRuleEra.net

 

[boo1]

Sometimes we repeat repeat posts...

 

[JStephen]

You might approach the issue from the opposite viewpoint and ask if there is anything that requires a specific wind load at all times. Building codes are not normally applied to movable equipment. You mention cranes, for example, and they typically are not rated to lift in heavy winds. A crane with long boom may not even be rated to have the boom up during high winds, much less be picking anything.

 

[McSEpllc]

Hi hchiutx,

I am not familiar with the Canadian Code, the IBC code used in the US though did away with the general allowable stress increase for transient loads with exception of wood structures. This is dealt with in Section 1605.3.11.

Eric McDonald, PE
McDonald Structural Engineering, PLLC

 

[steele6707]

ASME NUM-1-2000 is titled "Rules for Construction of Cranes, Monorails, and Hoists (With Bridge or Trolley or Hoist of the
Underslung Type)". There is a 2002 Addenda to the document. I reviewed the document at Linda Hall Library and copied a few pages. Wind loads are typed as operating wind loads, stored or out of service wind loads, and extreme (tornado) wnd loads. ASCE 7 is referenced for stored wind loads. Section Num-III-8000 describes load cases, design criteria and allowables. (They use a percentage of yield for some stress or use AISC ASD and then modify the result.)