Best Box Truss - Advice

[johnnypalmer]

Hi All,

 

It's about time we got some serious box truss. Up until now, we have been using trilite for everything, but I need a system that can be used for the following:

- Upright supports on stage (up to 6m high would be great)

- Flown lengths up to 20metre span for light rigs

- Versatile corner pieces

- Also offer good value, we will start with eight 2m lengths but need to work towards a full stage ground support. We will probably buy secondhand

 

It was suggested to me to get the Litec QX40S system.

 

Is this system good? What are other systems that would suffice?

 

Thanks

 

Johnny Palmer

www.sxsevents.co.uk

[Jivemaster]

With proper trussing every piece should have its entire history from birth - serial number and inspections all logged. Don't buy truss without this provenance. Should you also buy some ready calculated designs to ensure that all your trussing is loaded within safe rating.

[RogerB]

With proper trussing every piece should have its entire history from birth - serial number and inspections all logged. Don't buy truss without this provenance. Should you also buy some ready calculated designs to ensure that all your trussing is loaded within safe rating.

 

Hi all

 

Jivemaster is entirely right. A few things you might find useful:

 

At 60' span (quite specialised and ambitious by ground support standards) the horizontal and vertical trusses will have entirely different specifications.

 

Although there are always exceptions, a good rule of thumb is that any horizontal truss should be no more than 25 times longer than its depth. (The ubiquitous A-type or GP truss is 0.5m deep and is only really happy up to 12.5m, which proves the concept).

 

Consequently if you want to do 60' (18m) spans you need a truss around 75cm deep, which gets into the 'Heavy Duty' rating from most manufacturers. Assuming you use corner blocs with internal wheels (sleeve blocks) to fit around the masts, then any deflections on the main spans will try to bend the masts, so they need to have bracing designed to resist this. Most readily available trusses don't work in this way.

 

If you are going to buy bits to make your own ground support, you have to fully understand the difference between tensile and compressive forces. If you don't, then don't become a ground support designer!

 

Hope this helps

 

RogerB

[Paul Jordan]

All the truss manufacturers are able to give you advice on what you can and can't do on their products.

 

Tomcat for instance has standard ground support and roof (covered) systems, which already have the engineering done for you. Most of the other manufacturers do too. This means that if you purchase a standard system, the limitations, operational limits and safe loading calculations have been done for you and this document should accompany the supply of the items purchased, so that you have it to present to your client or H&S body before erection.

 

Again just to reiterate an earlier thread, each section of truss or individual item, should have a unique serial number. You should have documentation from the manufacturer of the equipment saying that the item was manufactured to their satisfaction with regard to quality and material of construction. You could call this the items "birth certficate". Each item should then be inspected prior to and after each use by a competant person withing your organisation and this should be documented in your company system against each item. You should then also get the products checked once or twice a year by a third party under a documented examination scheme, using the LOLER regulations. Defective products should be taken out of service and either repaired (again by the manufacturer or destroyed if beyond economic repair, so that they can't find themselves back in the system/industry again). By doing this you are doing all you can to ensure that the products you are using are always "fit for purpose" and should anything happen with the products, which is notifiable to the HSE, then this documentation can be produced and handed over to show that you have at least examined and maintained your equipment on a regular basis.

 

Just to back up what Roger has said, if you don't understand how the imposed loads are being dealt with in your structure, then you need to rely on someone who can... a good starting point should be the manufacturer of the equipment you are using who will be always happy to help you.

 

If you need any further information ro clarification, please do not hesiate to drop me a line

 

Best Regards

 

Paul Jordan

Technical Manager

Tomcat UK / PCM Ltd