Wind load calculation for Belt Conveyor Truss design 1

[am]

I am designing some standard conveyor belt trusses. I got all the belt details, carry & return idler details, material loading etc. However, I am looking for any good reference for wind load calculation. The trusses, walk ways, cable trays, service pipes etc all have contribution in wind loading. Again, adding their effect individually may lead to unrealistically high wind load. Also, wind load profile on belt profile itself is subject of further study! Probably specific wind tunnel test results with all the ancilliaries will predict appropriate drag coefficient. Unfortunately I do not have such data available to me. I am wondering if there is any good reference available for wind load calculation for this type of structures. I am following Australian standard for wind loading but I failed to find any good guidance in this matter. Any help will benefit me! Thank you all in advance.

AM

 

[dbuzz]

You’re correct to assume that wind load will be applicable to the truss/walkway steelwork, belt , piping and cable tray.

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, assume vertical profile of 0.5m. For wind load on the piping and cable trays, as per AS1170.2.

A ‘shutdown’ windspeed of 20m/s (or more) may be appropriate for combination of wind loads with dead loads, maximum walkway live load and normal or flooded-belt material load. Refer to AS4324.1 “Mobile equipment for continuous handling of bulk materials” for more information on this. The ultimate wind load may only be applicable for the ‘1.2G + Wu’ and ‘0.9G + Wu’ combinations.

The worst combination of gravity loads (dead load, walkway live load and flooded-belt material load) is usually the design case for the chords and the vertical struts and ties. The wind load will influence selection of the horizontal struts and ties and may only slightly influence the chord size.

 

[am]

dbuzz

Thank you for your input. I am glad that I am on the right track. I did not consult AS4324.1 yet but will do.

Best regards

AM

 

[jike]

Is there a possibility that the Owner may want to hang siding on the conveyor bridge in the future? For instance, to keep rain or snow out. You might want to consider that and design for a wind load not less than on the full projected area of the truss.

 

[dbuzz]

jike, there's not much snow to worry about in Australia! For some dry materials, powders and moisture-sensitive materials there may be a corrugated light-gauge metal cover (semi-circular in section) over the belt and idlers.

 

[J1D]

am,
From what I can recall. The wind load calculation of conveyor truss has nothing very special. The load will come from:
1. wind on the truss members, the same way as you calculate the load on a 3D open web truss. If icing is present, members will be deeper.
2. wind on the belt, use the project height as dbuzz suggested, also consider the material build-up height.
3. wind on skirting panels, if applicable, sometimes this is significant.
4. wind on walkway/platform, you can consider the walkways on both sides if present.
5. wind on catch panels, if applicable.

When a conveyor has a large span, or if you are designing the high-rise conveyor truss near the pulling head, wind load will play a big role in design

 

[Lutfi]

ASCE 7 98 and 02 has section and provisions to compute wind pressures on trussed and latticed structures.

ASCE 7-02 can be purchased from

http://www.asce.org

There are also software packages that are excellent to compute wind loads using ASCE 7 standard. One of which I happen to use and is written by Standard Design Group (SDG). Here is their web site address

http://www.standardsdesign.com/Default.htm

Good luck

 

[am]

Many thanks to all of you for your valuable input.

However, I would still like to see if there is any document available where they have indicated the drag coefficient for carrying idler + return idler location. Width, Shape of carrying idler and return idler and spacing between them will have some special drag coefficient for wind load calculation.

On another token, I am wondering if there is some special requirement to be satisfied with respect to the natural frequency of the conveyor and idler rotation or belt speed.

Thank you all again.

Regards

AM

 

[dbuzz]

am,

I've never seen the wind loads calculated for carry or return idlers. Also, I've never seen a natural frequency check undertaken for the exitation of a conveyor truss by the belt/idlers.

Have you seen a belt conveyor in operation?

 

[aggman]

am,
We once had a situation, (before I worked here) where we had a large stacking conveyor that was carrying very large rip-rap, 30" minus along a conveyor at 200 ft/min. The stacker was configured like a guyed pole, cables slung from a single point to support the truss. To make a long story short we ended up with a fatigue failure on a plate due to the slow cycling of heavy rock bouncing over idlers. This is the closest thing I have ever encountered that would be considered a dynamic failure. Typically aggregate particals are small and travel fast. This makes them act as a uniform distributed load, and any dynamic effects can be absorbed by impact factors. CEMA has impact factors given in their 5th edition which work well (Table 5-6). You can certainly calculate the frequency of the load as it is proportional to the belt speed and the idler spacing. Typically dynamic (time-history) analysis's account for peak or spike loads, and the response of the structure some period of time after that. I can't see how you could analyze the structure dynamically for a continuously cyclic load, especially since the load continuously varies (Feed is typically not perfect). Typical practice in the industry is to design for uniform load, and the worst case of surcharged belt load, and the load calculated based on the belt speed and average tons per hour, multiplied by the impact factor. Only occasionally will the second method control.

 

[am]

dbuzz

My sincere apologies - I meant belt, not idlers. I understand that some company in Australia undertook this study with wind tunnel test results; unfortunately I do not have copy of their report.


aagman

Your explanation on time-history analysis is very helpful.

Thank you all for your valuable input.

Regards

AM