Stutwo Posted March 15, 2006 Share Posted March 15, 2006 :P - Split / copied from here :) http://photos-219.facebook.com/n13/151/19/193106211/n193106211_30266219_871.jpghttp://photos-247.facebook.com/n13/151/19/193106211/n193106211_30266247_9648.jpghttp://photos-162.facebook.com/n13/151/19/193106211/n193106211_30266162_8824.jpgA few photos from the Engineering and Science Ball held last Saturday in the Passenger Shed, Empire and Commonwealth Museum. I was the joint technical manager... Hi David, Just out of curiosity, was anything used to safety that front truss, or was it free standing? :) - Pictures edited in for context Link to comment Share on other sites More sharing options...
Tomo Posted March 15, 2006 Share Posted March 15, 2006 Just out of curiosity, was anything used to safety that front truss, or was it free standing?There's nothing to safety it to.The reason for a goalpost was because there were no rigging points in the air. In fact, I'd guess that there is never any reason to safety a goalpost - if you've got something to safety to, you've got something to hang it from, and a hung truss is always better than goalpost - if only because you can't possibly knock it over. Link to comment Share on other sites More sharing options...
Stutwo Posted March 15, 2006 Author Share Posted March 15, 2006 Fair argument, just wondered about bracing it to the fairly large truss structure behind it once it was up, it seems a fair height and weight. I'm always paranoid about free standing goalposts, though I'm sure it was perfectly safe, was just curiosity. Link to comment Share on other sites More sharing options...
Andrew C Posted March 15, 2006 Share Posted March 15, 2006 I can't help wondering where the harnesses are on the two up the truss... It does look good lit up though! Link to comment Share on other sites More sharing options...
woody74 Posted March 15, 2006 Share Posted March 15, 2006 In fact, I'd guess that there is never any reason to safety a goalpost - if you've got something to safety to, you've got something to hang it from, and a hung truss is always better than goalpost - if only because you can't possibly knock it over. This comment scared me. It takes far less weight per point to safety a goapost than to fly a truss because you are not taking the full weight of the truss on a safety, just the lateral force needed to knock it over. Link to comment Share on other sites More sharing options...
Pete Posted March 15, 2006 Share Posted March 15, 2006 Somehow don't think harnesses would of helped although the piece of truss at the back seemingly supported by a zarges does concern me. Link to comment Share on other sites More sharing options...
DSA Posted March 15, 2006 Share Posted March 15, 2006 the piece of truss at the back seemingly supported by a zarges does concern meNo - its OK!! It is just the angle of the photo!! The truss was supported by being an articulated corner at the top, and held to the upright with a short steel. David Link to comment Share on other sites More sharing options...
hughesy Posted March 18, 2006 Share Posted March 18, 2006 I can't help wondering where the harnesses are on the two up the truss... Just wondering if a fall arrest lanyard that stretches to 2m after a fall would have helped if you fell off that truss, which is at 3m???? Link to comment Share on other sites More sharing options...
Tomo Posted March 18, 2006 Share Posted March 18, 2006 This comment scared me. It takes far less weight per point to safety a goapost than to fly a truss because you are not taking the full weight of the truss on a safety, just the lateral force needed to knock it over.That cannot be true. If the lines are not vertical, you are simply transferring the moment in one direction only from the goalpost to a different structure.Unless you stabilise in both X and Y, you acheive nothing except varying the balance of probability - safety to the stage, and the structure won't fall into the crowd, but can fall onto the cast. Not acceptable.If you stabilise in X and Y, then they must be taut and you've put in guy lines, not safeties. They do increase the stability of the structure and are a great idea. Let's say you have vertical flown lines going from points in the roof to the top of a goalpost. There is a small amount of slack in them, as otherwise you've started to pick up the truss. If the safety will not take the full weight of the goalpost, then it is not a safety: The goalpost tips slightly, the top lowers and comes forward or backward until it loads the safety lines - the load on these lines is not calculable, and varies hugely depending on the amount of slack in the lines.The base of the goalpost then slips sideways, as the load is no longer straight down.This increases the load on the points, which in turn causes a greater sideways force, until the goalpost is no longer mostly groundsupport and is now mostly flown. The goalpost now has a very uneven loading, which may be enough to collapse the corner struts if it was near the rated max, leaving the entire weight of the goalpost on the flown points. While it wouldn't happen every time, there are several failure modes which would load the entire weight of the goalpost on the points. If they can't take it, they aren't safeties. If the base is not large enough to assure safety, then no arrangement of flown safety lines will be sufficient unless they can take the full weight of the goalpost, in which case you'd be better off flying it. Link to comment Share on other sites More sharing options...
richard Posted March 18, 2006 Share Posted March 18, 2006 I would usually brace a goalpost with tube back to a sold point (in this case it could probably be your rear truss). I would definatly not want to just rely on the manfrotto lifts, I have seen the amount they flex once they are up! Link to comment Share on other sites More sharing options...
Jamtastic3 Posted March 18, 2006 Share Posted March 18, 2006 What about the truss that's just visible in the second picture on the right. Was that free standing as well (considering that it looks like it would be right over the crowds)? Link to comment Share on other sites More sharing options...
Tomo Posted March 18, 2006 Share Posted March 18, 2006 I would usually brace a goalpost with tube back to a sold [sic] point...And that is a good idea. Bracing is almost always a Good Thing. What worries me is when someone fits a safety that would never catch the thing it's supposed to.In my view, that's worse than no safety at all! -PS, thanks for the topic split! Link to comment Share on other sites More sharing options...
Guest lightnix Posted March 19, 2006 Share Posted March 19, 2006 I can't help wondering where the harnesses are on the two up the truss...Can't help wondering where the hard hats are on everyone else - unless that's one sitting DSR on the small piece of truss in the last picture :) Link to comment Share on other sites More sharing options...
dbuckley Posted March 19, 2006 Share Posted March 19, 2006 Whereas I'm not qualified to comment on the safety aspect of this assembly, I do note that there is some irony that this is the "engineering and science ball", these are the folks who will be building the buildings your offspring will be flying truss in/from... Link to comment Share on other sites More sharing options...
Penny Posted March 20, 2006 Share Posted March 20, 2006 There was really nothing to brace truss to. No rigging points whatsoever in the venue, the only thing it could potentially have been braced to would be the on stage truss structure. In the event of a fall, that would have been pointless as it would simply have pulled it over towards the stage rather than provided any useful bracing. I can understand that situations exist where truss bracing may be useful and possible, this wasn't one of them. We had a competant professional rigger present (not a student), he was happy with it. That is a hard hat sitting on the DSR bit of truss, plenty were available for any crew who wanted to use them (as well as other safety equipment such as gloves and ear protection), and most of the time they chose not to. As for harnesses, Hugesy has a point. You'd be standing on the stage before the harness had any effect! Link to comment Share on other sites More sharing options...
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