Belt Conveyor Truss Design

[aggman]

I have been asked to design some standard truss parallel chord frames, with allowable spans for particular belt widths. The trusses are to carry limestone and coal, and are to be designed to support all the bells and whistles, (walkways, hoods, idlers, pull-stops, and electrical). My question is as follows. Normally I have engineered conveyors for a specific application. This means that the TPH and the pulley resultant loads are known. For the standard truss designs these properties are not known. I have found a previous engineers calcs for similar work and all that he did was design the truss for a uniform moment of 1/8 wl^2, due to the distributed load. While I would agree that would give you the worst case chord force, I am not sure that the loadings are really ideal. He used a surcharged belt with 20psf on the walkway, but of course had no way to account for the compression in the truss due to the conveyor drives. Is this a good way to design the truss, since the likelyhood of a surcharged belt and a 20psf walkway load all happening at once is somewhat unlikely? If not what would you recommend? Thanks in advance for your help.

 

[deckard452]

I've designed a few conveyor trusses and agree it would be difficult to design a standard truss for an unknown load. Perhaps you could design a truss layout and tablurise max span according to max load.

As for compression due to drive forces These are normally taken out at head frame and tail take up. To take compression all the way down a conveyor truss system implies a continous structure with possibe thermal expansion problems between your local max and min temperatures. Best to not allow for this compression in individual trusses and incorporate sliding joints whwre appropraite.

Considering surcharged belt and full live load - What's the first thing they'll do if the system chokes up? - they'll send as many people as possible to go and clear it. It is also likely that a lot of material will end up on the walkways. So I think this is a valid scenario.

Also wind needs to be considered - under normal operating, your maximum allowable wind (before shut down) will increase compression on the top windward chord and tension on the bottom leeward chord.

I trust you are using computer models so covering all these eventualities should be a breeze.

 

[nnjunger]

I know it has been a while since there was any activity on this thread, but I had a question regarding what kind of software you are using to model these scenarios. I have an existing conveyor that we want to modify (move legs, enclose, etc.) and I am concerned that the framework will not handle the loads as originally desinged. Thanks in advance for the assitance.

 

[aggman]

I use RISA 3D. It is a general three dimensional structural analysis program. It is quick, and easy to use. Typically I would model the truss to the exact dimensions on the drawings, (for new truss), apply loads, and then analyze the different load combination.