Slick litebeam load apex up

[numberwrong]

The load table on the manufactures web site doesn’t state whether the data is referring to apex up or down. I was under the impression that apex up is about 50% weaker then apex down with aluminium trusses. The only cross sectional diagram on the slick web page is apex up.

 

 

 

How would I work out an apex up calculation?

 

 

 

Cheers

 

 

[trussmonkey]

give the manufacturers a call or Total Solutions Group.

 

I have always worked on the basis that the standard way to rig a triangular truss is apex UP.

 

 

TM

[ianl]

the new slick litebeam (with the eggs and egg cups welded in the end) is the same load either way up

 

the mk1 slick litebeam with the eggs and egg cups riveted in the ends is stronger one way up than the other (think apex down is weaker)with the strongest way being the same as the new style

 

you need to find an older copy of the load data that shows the apex up and apex down figures

[mac.calder]

the standard way to rig a triangular truss is apex UP.

 

Disagree with that statement - The only times I tend to see tri truss apex up is when there is a necessity to split the hangs, like a screen and a drape on the same truss line, or something with a bracket that requires apex up truss (like a big projector). Even then, the preference seems to be for 300mm box truss.

 

Another vote from me on contacting the manufacturer.

[trussmonkey]

the very fact that there is an absence of load tables for apex down would suggest to me that the most common usage would be apex UP.

[mumbles]

From an engineering view, given the comparable tensile to compressive strength of aluminium tubing I would have expected triangular truss to have a higher bending moment capacity with 2 chords in compression and 1 in tension. So in a simple span between 2 non-moment carrying points I would suggest apex down is stronger. As soon as you have a continuous span across 3 or more points, or you have a cantilever then it would depend on the bending moment along the span to determine where it is greatest and which side of the 'beam' it is on, as to whether apex up or down is more appropriate. A load table can only give you half the story and so is useless unless you match the example load precisely....

 

But as a general rule, assuming a a simple span on 2 points, or an even(ish and not too excessive) loading across more point I would have thought apex up would have the lower strength than apex down. Definitely unless it is on stands, or you need 2 barrels to hang on, then I would normally choose to hang it apex down.

 

THIS IS NOT A GIVEN RULE SO DON'T JUST TAKE MY WORD FOR IT!!!

 

To clarify: I studied civil engineering but graduated 3 years ago and have been a lampie ever since. I still understand all the engineering principles I've talked about BUT I'm not nor ever was a materials engineer so without the specifications for the relevant grade of aluminium alloy all of this is still conjecture.... I am happy I know what I am doing well enough to design a simple rig, and have worked with enough much more experienced riggers to know that they have confidence in me too, but if you don't understand everything written above then maybe, nay definitely, you need some more qualified to help. I don't want to piss anyone off as I know lots of brilliant riggers with no formal engineering training but I have also seen lots of (younger) people just try and have a go at it thinking it can't be that difficult when they really don't understand what they are doing.

[rgye]

All the illustrations on the Litebeam literature http://www.slick-truss.com/products/litebeam_corners.php?product=litebeam seem to show horizontal members with apex up. In situations where you have a plate connection at the top of a leg (ie where it's not practical to use a 2/3/4 way corner) you really don't have the option.

[rgye]

From an engineering view, given the comparable tensile to compressive strength of aluminium tubing I would have expected triangular truss to have a higher bending moment capacity with 2 chords in compression and 1 in tension. So in a simple span between 2 non-moment carrying points I would suggest apex down is stronger. As soon as you have a continuous span across 3 or more points, or you have a cantilever then it would depend on the bending moment along the span to determine where it is greatest and which side of the 'beam' it is on, as to whether apex up or down is more appropriate. A load table can only give you half the story and so is useless unless you match the example load precisely....

 

But as a general rule, assuming a a simple span on 2 points, or an even(ish and not too excessive) loading across more point I would have thought apex up would have the lower strength than apex down. Definitely unless it is on stands, or you need 2 barrels to hang on, then I would normally choose to hang it apex down.

 

 

Intuitively I would have thought the opposite. As mumbles suggests, the upper chord(s)are in compression and the lower in tension. The compressive and tensile elasticity of aluminium are about the same, so that will make little difference to the 'sag' of the loaded truss whichever way up it is (assuming it is supported at both ends). But the yield point of aluminium is surely much lower in tension than in compression. So for maximum strength before failure you would want the double chords in tension and the single in compression - ie, at the top.

[Joe Mapson]

Hi

Load tables for apex up and down are on Total website

http://www.totalsolu...litebeamtab.pdf

Used LB in both configurations

Cheers

Joe

[mumbles]

Intuitively I would have thought the opposite. As mumbles suggests, the upper chord(s)are in compression and the lower in tension. The compressive and tensile elasticity of aluminium are about the same, so that will make little difference to the 'sag' of the loaded truss whichever way up it is (assuming it is supported at both ends). But the yield point of aluminium is surely much lower in tension than in compression. So for maximum strength before failure you would want the double chords in tension and the single in compression - ie, at the top.

Except that if you look at most of the pictures of truss failures over time you'll see it is the side in compression that fails. Because the tensile and compressive strength are similar it will fail under buckling due to the thin wall and the narrow diameter before the yield point is reached. While it shouldn't reach a buckling point condition as the unrestrained length between the bracing chords is short, the failure mode will damage the weak welds first, increasing the unrestrained length, and then causing buckling.

 

As I said before I haven't sat down and modelled a piece of truss so don't take what I've said as a given, it is just personal engineering opinion based on most failure cases and intuition. If anyone on here has actually modelled truss failure, for manufacturers or for Uni projects etc I would be really interested in the opportunity to discuss my own assumptions and thought.

 

Thanks

[rgye]

This gets more interesting and more confusing as the discussion develops. I take mumble's point about buckling occurring before yield, but the table Joe refers to is unequivocal - apex up is very significantly stronger. The deflection seems roughly the same per kilo regardless of orientation, as I would have expected.

 

As mumbles suggests, some authoritative maths would be good to see.

[numberwrong]

Hi

Load tables for apex up and down are on Total website

http://www.totalsolu...litebeamtab.pdf

Used LB in both configurations

Cheers

Joe

 

 

Cheers - it seems that apex up is stronger according to this load table-

 

For a 10m span central point load is:

49.7kg Apex down

116.8kg Apex up

 

 

 

 

 

[ianl]

as I said before (and I'm a slick litebeam owner and a rigger, and I have the charts , and have talked to the manafacturer)

 

with new style slick litebeam (mk2) it is equally strong either way up ( or rather the published figures are valid for the truss to be either way up)

 

for the mk1 slick litebeam where the couplings are rivited to the end of the trusses rather than welded, if you use it apex up the current data is also valid. if you use it apex down, the single cord that is at the bottom and under tension (and specifically the rivited conection) is the weak link and you need the "mk1 litebeam apex down load data"