Wind Load on Conveyor Truss? 2

[sdz]

Does anyone know of a reference for calculation of wind loads on conveyor trusses? As well as the main truss which is typically angle chords and bracing there are walkways, railings, cable trays, belt and idlers, and possibly a belt cover. I think the coefficient of drag when it is all added up could be up to 2.0 x the gross area.

Have there ever been any wind tunnel tests on this?

 

[SperlingPE]

I would start by looking in ASCE 7.
Next I would check to see if there is an industry standard (most likely based on ASCE 7).

 

[JStephen]

I have found in times past that "exposed structural steel" seems to be neglected in some of these building codes. However, there are "Rooftop Equipment", "Open Signs & Lattice Frameworks", "Trussed Towers" in ASCE-7.

 

[CESSNA1]

SDZ:

Just be careful you do not repeat the Tacoma Narrows Bridge failure of about 1940. In that engineering failure the the vortex shedding frequency winds excited the resonant frequency of the bridge. I know of another bridge (Commmodore Barry, Chester Pa.) that also vibrated, but not as badly as the Tacome Narrows.

Regards
Dave

 

[SperlingPE]

My wife worked for a manufacturer of conveyor supports for grain bins. They used ASCE 7 for the wind loads. They produced angle braced towers and catwalks.

 

[aggman]

sdz,
I have always used ASCE 7 loading coefficients for open signs and lattice frameworks. I did some research on the topic several years ago and I read (I have forgotten where) that the normal force coeficients range from 1.6 to 2.0 for parrallel trusses placed somewhat close together. This seems to hold up in conveyor design also. If the conveyor has hoods I use the arched roof coeficients from ASCE 7. (This will be your worst case). If the belt and idlers are not covered, I use the open signs coefficients on the projected area, measured from the top chord. This seems to give good results. Back in the old day's people around here used 20 - 30psf depending on the height and we have never had a failure in 26 years. I think if you look into this methodology you will find it satisfactory. If you are nervous, don't consider the low importance factor. The trussed tower force coeficients are another method, but my experience, including hurricanes, seems to agree with the open signs and lattice frameworks method.

 

[dbuzz]

A drag coefficient of 2.0 on the "gross" area of the truss seems excessive.

See similar discussion of similar query at thread507-102134.

 

[sdz]

Thanks for your replies, everyone.

aggman, is that force coeff 1.6 to 2.0 based on gross area?

I am in Australia and using AS1170.2 which is our wind loading code. It was from applying that with shielding on downstream members that I got the factor I quoted. Our code does not directly address conveyors and that's why I would like to find any research data that would confirm or refute my calculations. I found the load from walkways and cable trays, etc., was a significant part of the load.

 

[Lutfi]

ASCE 7 and TIA 222-F standards have provisions from trussed systems. I would use either one of them.

Go to this link:

http://www.c-conceptsinc.com/files/example1.pdf

it has a hand worked example for a steel tower wind loads using TIA 222-F. ASCE protocol is similar to this one. Although it is for steel tower, in reality it is no different than a conveyor.

I also have an old study done by British wind group that I have used on latticed trusses such as conveyors.


Lutfi

http://www.cdeco.com

 

[aggman]

sdz,
The ASCE 7 provisions use Cf from 1.6 - 2.0 based on the ratio of net area to gross area. The calculated wind pressure is then multiplied by the projected net area.

 

[dbuzz]

sdz,

I'm an Australian engineer too.

For wind load on the steelwork, use AS1170.2 Clause E2.3 “Multiple open frames” or Section E4 “Lattice Towers”. Some design guidelines simplify this by making the following assumptions: terrain category 2; wind acting 15m above the ground; and drag coefficient of 2.0 on all steel sections.

For wind load on the belt and idler guards, assume a constant vertical profile of 0.5m.

For wind load on the handrail, piping and cable trays, as per AS1170.2.