Global and Litec truss - spokes not following contour through joins

[Dave lee]

Not sure if anyone can help....

 

Last weekend I started using my new 3x 2 metre QX30 truss and to my disappointment have noticed the webbing does not flow from one truss to another.

 

IE it should flow like this.... / \ / \ / \ / \ / \ / but it flows like this.... / \ / \ / / \ / \ / / \ / \ / you get the picture..

 

I'm know I'm being a bit of perfectionist but aesthetically it looks bloody awful.

 

What do I need to do to make it flow?

 

If anyone could help me with this, it would be really appreciated.

[Tom Baldwin]

Rotate the middle stick 180 about its long axis.

[Dave lee]

Hi Tony

 

We tried that and no matter what we did it never matched up.

 

dave

[David Lee]

Hi Name sake...

 

visually it looks awful, plus, I have been reliably informed it reduces the load you can put on the truss quite dramatically. I'm sure a rigger will be along to explain it better than I could hope to.

 

I've come across truss like that before, whatever you do you cannot make it correct. If you call the manufacturer they will usually say it is ok. I presume that the swl is either calculated for one piece of truss (no joins) or factors in the shoddy manufacturing where it leaves you unable to do it properly.

[Kaboom25]

Personally I have no experience with the Litec stuff but I know that Opti-Trilite will recommend that the zigs and zags always go in the zig-zag formation. BUT try doing that with an TriLite 200 system with 3m lengths in it - there is always one or two ends that dont match.

 

As previous posters suggest this is partly to retain the structural strength of the system but it also make it look nice too!

 

HOWEVER - if you use Prolyte or Milos type trussing then it makes no difference in terms of strength if the truss is connected with the diagonals going the same or opposing ways. This is because these types of truss are rated for each individual piece. They dont rely on a zig or zag from the adjoining piece to keep rigidity - they rely on the piece next to it as a whole.

 

So it might be worth checking with the manufacturer about what the system design is based on. But as before I would always try to get the truss going in some form of symmetry just so it's aesthetically pleasing.

 

HTH

 

CC

[flypig]

Just thought I'd add my two cents worth to this.

 

The principle of a stick of truss works likes this.

 

When a load is applied to a truss, (usually) the top chord is in compression (being squeezed) and the lower chord is in tension (being stretched). The forces in the truss actually change continuously from the top chord to the bottom chord. This means that the middle is neither in compression nor tension. These forces act in bending fashion (or moment) on the middle of the truss. By introducing either a diagonal or horizontal side webs between the top and bottom chords these forces are distributed more evenly toward the supported ends of the truss.

 

It should also be noted that the lateral spreader bars between the chords (the bars that link the two top chords and/or the two bottom chords) perform the same function as the side webs, hence the requirement to rig the truss the right way up.

 

In most rigging situations we are placing a lot of these sticks together. Ergo, if the principle works for one piece of truss then it must also work for the entire length or it will fail.

 

I would be very interested to see the calculations from a manufacturer who deems that "They don't rely on a zig zag from the adjoining piece to keep rigidity" (the operative word here is 'adjoining' of course).

 

The symmetry of the web is an essential part, not just aesthetics.

[Dave lee]

Hi all and many thanks for your replies.

 

I'm confident we're not overloading the truss as we're only hanging a pair of Mac 250 Kryptons on each 2m section.

 

I did however get a reply from Litec on this and they've advised me that these truss sections will not match up.

 

Apparently I now have to buy their QX30S truss if I want the webbing to match!!

 

Wish I was told this before I handed over my cash !!

 

dave

[djw1981]

With all due respect, if this was a first entrry into the russ world, or you buying a new brand of truss, I assume you ahd a demo, at which teh none zigzag would have become obvious.? :)

[Chris Higgs]

ALWAYS follow the manufacturer's instructions when assembling trusses. Don't guess.

If there is no advice on assembly available from the manufacturer, it probably doesn't matter how it goes together - BUT observe the loading information, that may be the factor that means it doesn't matter how the truss is assembled. The only real constant is that most trusses are used to support a vertical loading and therefore generally, the diagonals need to be on either vertical face of the truss.

 

Some trusses require consideration of bracing patterns, some don't.

That will be in the operating manual/instructions.

Very often the fact that a perpendicular is present at the end of a section will mean that actually it doesn't matter if diagonals run alternately, but it usually looks better when there is a consistent pattern. In one well known design, the diagonals in the centre of the span experience no force at all, but the manufacturer doesn't know how many sections you'll be using, so they still put them in each section, obviously.

The first diagonal at the end of a span will often slope upwards, but again there are well known exceptions to this rule. For example, Slick Mini Beam was designed to be used with the end diagonal sloping downwards when used in a single run but when used with a cornerblock it doesn't matter. (The corner stiffens up the end and resolves the bracing requirements)

 

The most important thing is to follow the instructions - don't listen to those who may be very experienced but haven't read the relevant manufacturer's manual and understood it.

If it's Litec QX30, those are the instructions you need.

 

All trusses rely for their strength on a balance between materials and its proportions, self weight, connection methods and the way the members are laid out in terms of distance apart and angle to name a few. They are almost all different - one of the reasons not to mix types together in a system.

[Tomo]

Ok, having read the instructions - it doesn't matter on the Litec QX30 truss system, as it's actually impossible to make the chords maintain the pattern between sections.

 

Shame - I'm using some of the stuff next week, and I don't think the boss has realised this yet.

Could be interesting - hopefully we can head off the argument before it happens!

[adamwb]

Dear Dave,

 

 

As the UK distributor for Litec Truss I thought I should comment on this.

 

 

You are correct, the QX30 truss you are using does not have continuous diagonals when you meet two sections of truss together. This is the specific design of the truss and the manufacturers published load calculations are based on this design.

 

 

You will notice when the truss is fitted together, that where the diagonal on the first truss of ends, and the next diagonal starts on the adjoining truss, that the space where the end plates are is equivalent distance to a diagonal. This was the intention on this original design.

 

 

Litec have now developed a version of the QX30 truss, called QX30S, which has a new configuration of the diagonal chords, giving the continuous look you are talking about. Again the manufacturer offers calculations specific to this "S" version. In addition to the design of the diagonals, it also has a newly designed end plate, which is heat treated to give greater strength. (The new "S" version is in fact stronger than the original version.)

 

 

In summary, neither truss is "wrong". Some applications require the better aesthetic appearance and in others it's not so important.

 

 

One of the good points of Litec as a manufacturer is that they do listen to feedback from their customers and always try to improve their product range, hence the development of the "S" series.

 

 

I am lead to believe from my colleagues that there is a proposal in place to swap your truss for the S version.

 

Please feel free to PM me if needed.

Adam

[Steve Cavill]

Hi,

 

I use this trussing system daily. It is designed to look like this.

 

Put 2 bits together and take a closer look...where the pieces join is where the opposite angle strut should go...Its reinforced at the ends so that it is stronger, personally, if the strut was there it would look rough.

 

Thats my input..

[whitehousejamie]

I have 12 sections of the QX30 3.0m. The configuration isn't a problem for me, it looks fine as it is.

[Steve Cavill]

Sorry, first message was left in a bit of a rush...

 

The system goes like this \/\/\/\/\\/\/\/\/\\/\/\/\/\\/\/\/\

 

But if you take a closer look when you put it together it goes like this... |\/\/\/\||\/\/\/\||\/\/\| if you take a look at where the || are this is where your missing strut would be.

[rick@slick]

OK, so we've just bought some truss from Thomann International - it's Global Truss. We saw some at an event in Holland and it looked sturdy, was a good price, so we thought we'd go for it.

 

It arrived today, and quite frankly we are non-plussed.

 

The pieces look like this:

http://www.globaltruss.com/images/products/3DTR4079.jpg

 

there are 2 perpendicular spokes at the start of each, and then 7 spokes diagonally bracing along. This means that no matter how you arrange it, it does not follow the standard joining pattern of |/\/\/\/\||/\/\/\/\/\/\/\||/\/\/\/\/\/\/\/\| etc

 

it looks like this: |/\/\/\/||/\/\/\/||/\/\/\/\/\||

 

Now... I've seen truss be set back on big jobs for not matching up in the alternating spoke manner along the length - so surely this is just not going to be acceptable to health & safety?

 

Or is it ok? Please can anyone help? Do we need to send the whole lot back and get or money back and curse their name or what?