Asymmetric frame geometry for conveyor

[Ingenuity]

I have a new aggregate conveyor (not yet installed) that has to be lengthened with a new vertical support frame to be added. Due to some site obstructions the new frame will be asymmetric. The exterior geometry of the frame is somewhat fixed, but I can 'play' with the internal bracing configuration.

Is there a preferred internal geometry for such frames:

OPTION 1: Parallel bracing:

OPTION 2: Equal panel height:

OPTION 3: Not parallel nor equal height.

 

[jayrod12]

I feel the equal height ones likely make the most sense in terms of keeping the brace lengths most reasonable.

 

[KootK]

I have a very strong visceral preference for the parallel bracing option. I don't yet have a logical reason for that though. I'll noodle on it...

 

[Ingenuity]

Thank you for your input.

I too have a visual preference for the parallel bracing option - and makes the shop drawings a little more repetitious, but is does result in a tall lower panel with longer brace lengths, as jayrod12 implies.

Interestingly, the conveyor manufacturers seems to have no agreed-upon industry standards. I have a 3-panel symmetric frame where the lower two panels are equal height, and the top panel is shorter - I guess to avoid too steep of a bracing angle.

Conveyor manufacturers often use channels for the vertical legs of frames - some go with toes outward, other goes with toes inward. Across manufacturers, the conveyor spanning trusses are also all over the place too - some do LHS and RHS diagonal as symmetric, others do it asymmetric. Sheesh.

 

[SwinnyGG]

Parallel bracing and toes in on the channels makes most sense to me.

Toes in because I would think you'd want the stiffer side of the neutral axis on the outside where it's under tension.

Parallel bracing because, like Koot, to me it looks 'right' although I have no real rationale other than that.

 

[jayrod12]

I do see the allure of parallel bracing, especially from a connection detailing perspective. Realistically I guess that almost implies that direction would be better since connections cost more than raw member costs. I really could go either way.

I also feel your pain on the conveyor mfr's. The odd times I have to deal with them, it's never the same company and it's like having to learn their preferences anew each time.

 

[dhengr]

Ingenuity:
I think everyone’s ‘visceral preference for the parallel bracing option’/ ‘logical reason’ (per Koot), is that the parallel bracing option slightly improves the lengths and slopes of the top pair of braces. They might be able to be sized down a notch because of this, their slopes are not so steep from the bracing standpoint. The lower braces, while somewhat longer under this option are huskier members in any event, so they may be able to tolerate thier length increase a little better, and their slopes still look o.k. You might look at keeping the out-to-out width at about 8’, at the base. This should make shop fab and shipping a little easier.

 

[Ingenuity]

You might look at keeping the out-to-out width at about 8’, at the base. This should make shop fab and shipping a little easier.

I have no transportation issues as the frame is being fabricated by the Owner's internal welding shop who are very experienced in fab/welding. Transport is about 300 feet from the fab shop. But otherwise, I agree keeping it shipping-friendly is definitely a consideration.

 

[KootK]

Yeah, good looking brace angles and repeat connections. Those are some solid, logical reasons. Additionally, we usually go tension only bracing with this kind of thing anyhow, don't we?

@Inginuity: you got anything else to add on the "the pre-compression IS the reinforcement" thread? I want to add some meat to that one but would like to ensure that you've said your piece on that before continuing. I had the impression that a big reveal was in the works there by maybe I misread the situation.

 

[human909]

I'd generally be going for approximately equal heights so effective lengths of the main supports are optimised.

But for something that is only 5m tall I wouldn't overthink things unless this is a support being repeated 100 times. I which case it certainly needs some optimised cost design.

Last design I did for one of these was 25m high. I used I-section for the columns and HSS chevron bracing. 5 segments, effective length ~5m in minor axis.