ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  
Pages: 1 [2]  All   Go Down

Author Topic: a roof system question  (Read 4324 times)

Craig Leerman

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1389
Re: a roof system question
« Reply #10 on: August 26, 2004, 05:57:25 pm »

Hi all,

I would have jumped on this topic sooner, but I was trucking a show across the country the last three weeks and have not had daily internet access!

First, a Genie lift is not designed or built for roof loads, just a static balanced load of lighting or a truss. If any problems were to happen, the manufacturer would not be liable, and any insurance would not cover you for any losses or injuries, as you would have used a manufacturers products for a use not intended by the manufacturer.

Also, the standard Genie Lifts is not designed for uploading or side loading, just standard downloads. If any loading whatsoever is applied to the side of a genie, or any sudden uploading (like a gust of wind picking up the roof and lifting the masts in the towers) the Genies can and will fail.

There are many instances of Genie type lift roof and truss failures.

I personally have witnessed 3 roof failures and 2 truss failures with Genie and Genie type lifts.  Most were caused by a sudden change in the weather bringing in high winds. The winds simply either blew over the entire rig, or in one instance lifted the roof off of the masts, and then pulled the rig apart.  After the second lift/roof failure, I instituted a policy of not working on or under that type of roof system. These accidents were what got me into the staging business in the first place.

The third failure I witnesses was caused by overloading the lifts. The contractor had used guy wires to anchor the lifts to some 55gal water barrels for ballast. The roof system was comprised of 12X12 box truss with a tarp on top. Standard 6 can lamp bars were hung across the front and back of the truss roof for lighting. The entire rig probably weighed more than the 4 lifts could carry. As the contractor cranked the rig up, the guy wires exerted more stress on the system and one lift cable failed, causing the lift to retract. The roof system then came crashing down in a heap!  I was working on the indoor stages at the festival, and walked outside  after a coworker told me that the roof looked overloaded. I built the outdoor roofed  stages for that festival after that!  

I also have witnessed two lift failures that just had truss on them. One was from overloading. The lighting contractor was using two Genies to hold up a rear double hung truss 40' long. Because the 40' wide stage was against the back wall, they decided to place the lifts one each side of the stage and pick up the truss from the ends. Unfortunately, the truss was loaded with 60 cans, a bunch of color scrollers, 20 leko specials, 6 big moving mirror intels, and 3 ACL bars. On top of this load was also a rear black curtain.  With all the weight and strain on one side of each of the lifts, the capacity should have been reduced. One lift binded  when they were raising the load. With an uneven strain on the other tower, it started to shift slightly before the guy cranking it could stop. Then it simply started to topple over. Once the rig started moving, it kept up its momentum, and fell downstage, luckily just missing some stagehands, and  my backline.

The other truss failure was when a lighting company used 40' of double hung outside on 2 Genie Super Towers. They blocked the wheels, and put wood under the cranks to level the towers. During the show, a big wind simply blew the whole thing over anyway!

All roof systems have some element of danger to them, but using lifts as part of a roofing system should never be done.

There are two basic ways to ensure that a roof system will not topple over in a wind. The first is to use break away fasteners on the roof tarp that would allow the roof tarp to disconnect and blow in the wind, or tear off in a strong wind, leaving the framework and support intact.

The other basic way is to use a large rig that is sturdy enough and strong enough to stand up to large wing loads.

There is a third type system I designed that basically floated the roof truss and tarp system between large scaffolding towers. The rood was suspended by steel and spansets (with safety chains as a redundant backup)  The concept was that since I did a lot of shows in Maryland and Virginia by the water where its usually windy, I would make the roof "Ride" on the wind when it blew pretty hard (like 40+ MPH gusts)

The concept worked like a charm. The roof was static and just hung there when it was calm. Medium winds would sway the roof slightly, and big gusts or large winds would rock and lift the roof, allowing it to move and dissipate the winds energy.

The only problem was that many entertainers didn't like standing under a moving roof (no matter how over designed) and when a short gusts of wind did lift the roof, it would fall back down on the spansets, steelsets, steel and chains making a large "clunk" sound which unnerved a few performers.   After one season, I switched back to a large rigid scaffolding and roof system (which also Incorporated a break away tarp just for extra measure)  

I'm so old, when I was doing FOH for Tommy Dorsey, to balance out the horn section I would slide their chairs downstage and upstage to mix!

Pages: 1 [2]  All   Go Up

Page created in 0.036 seconds with 18 queries.