Look up into the air! Is it a bird? Is it a plane? No it's, it's.... Well it really isn't that interesting. It's not Superman, you know, just a piece of lighting truss. Of course like the mild-mannered Clark Kent, plain and boring on the outside, truss and the accompanying rigging are as strong as steel and do super feats to keep the lighting gear it holds from dropping out of the sky, and that's pretty important if you think about it.
So why is truss, pipe, and rigging equipment important anyway? Well, the lights have to hang off something. Usually that something is a catwalk, a pipe batten, or a truss.
Pipe, truss, and all of the equipment used to hang stuff from the building's structure is collectively called rigging and is one of the unsung heros of the lighting industry. It's part of the primary infrastructure of a lighting system and one of the unseen expenses of the system, as well as one of the most dangerous parts.?Anytime that you hang something above head height there is always a risk of injury or death if the item decides to fall. Incorrect rigging could fail and cause the lights hung with the rigging to fall.
Although the failure was caused by wind, the collapse of the truss roof at the Indiana State Fair in 2011 poignantly demonstrates the amount of destruction that can happen when a truss fails. As such, it has to be said that rigging is not a do-it-yourself kind of job.
1. Who installed your rigging system?
Not sure if it was it a certified rigger, or if it was done in-house? Most do-it-yourself rigging jobs that I have seen in both theaters and churches tend to be poorly done.
2. Does your system use dog chain, S-hooks, or dog clips to rig with?
All of these items are made with soft steel or aluminum and tend to bend open or crack and break under weight. Only welded link or forged chain rated for overhead lifting or rated steel air craft cable should be used for rigging purposes.
3. Are you using quick links or climbing carabiners for rigging purposes?
Ideally, shackles should be used in place of quick links and carabiners because a partially open quick link or carabiner can reduce the load rating of the item by more than half, causing it to fail at a much lower weight load than it is rated for. If you have shackles, are they "moused" with wire or zip ties so that the pin of the shackle can't work its way out over time?
4. Are you using cable or "Crosby" clips on your steel aircraft cable?
Were they properly tightened with a torque wrench to the manufacturer's specification? Are they attached the correct way? Do you inspect them every year? Cable clips tend to loosen with time as the cable stretches and settles. It is not uncommon to find cable clips that are not even finger tight or that are installed backwards, both of which greatly increase the odds of failure. Cable clips need to be inspected and retightened with a torque wrench every year. Instead, use cable swages [sleeves] as they don't work loose over time.
As I said, these are just a few of the common issues, but if you answered "yes" to a few of these questions-at the very least you probably need a rigging inspection. If you answered "yes" to a lot of these questions, you definitely need a rigging inspection, which may reveal you need to replace your rigging before it fails. Of course there are many theaters and churches where the rigging has been professionally installed, and when it is done correctly it can create a wonderful lighting rig.
5. How do you decide if you should use pipe or truss?
Well, each has its pros and cons, and you must decide based on application.
Lighting truss is a complex machine that is purposely designed to span great lengths and to hold large amounts of weight safely. Truss, while simple in appearance, is complex in execution as it has very particular handling, assembly, and hanging requirements.
Truss is especially good when the primary building structure has a wide spacing, since truss can easily span 40 feet between structural supports. It also tends to be able to handle more weight than pipe, and it comes in all shapes and sizes. Of course the size is determined by the application. The larger the truss the stronger it is; 12-inch and 20-inch box truss are common sizes. Truss is also more expensive because of the cost of the aluminum alloys and the more complex manufacturing process that is used to make it. Also, since truss easily bolts together, it is a better option than pipe for temporary use.
Like truss, steel pipe can be used to support lighting equipment, but pipe is lowly in its design and as such can only span a short distance before it has to be structurally supported; usually every 8-10 feet. Yet pipe offers some great advantages in that it is much less expensive, more readily available, and is lighter and simpler in its assembly, so generally pipe is the default product for permanent installations. However, in those instances where pipe won't work, truss becomes the go-to product.
Of course the real determination of what to use lies in the expert hands of an experienced rigger and the consulting structural engineer who determines where and how the rigging will connect to the building. Because unlike in the movies, Superman isn't going to be there to catch the equipment if it falls.
