Return-Path: X-Processed-By: Virex 7 on prxy.net X-Real-To: stagecraftlist [at] theatrical.net Received: by prxy.net (CommuniGate Pro PIPE 4.2.5) with PIPE id 4833349; Fri, 29 Oct 2004 03:00:36 -0700 X-ListServer: CommuniGate Pro LIST 4.2.5 List-Unsubscribe: List-ID: Message-ID: From: "Stagecraft" Sender: "Stagecraft" To: "Stagecraft" Precedence: list Subject: Stagecraft Digest #178 Date: Fri, 29 Oct 2004 03:00:14 -0700 MIME-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Disposition: inline X-Spam-Status: No, score=-4.6 required=5.0 tests=ALL_TRUSTED,AWL,BAYES_00 autolearn=ham version=3.0.1 X-Spam-Checker-Version: SpamAssassin 3.0.1 (2004-10-22) on prxy.net X-Spam-Level: X-TFF-CGPSA-Version: 1.4f2 X-prxy-Spam-Filter: Scanned For info, archives & UNSUBSCRIBE, see --------------------------------------------------- Stagecraft Digest, Issue #178 1. Re: Bizarre Multiple Catastrophic Truss Failure / rfc (long) by Cosmo Catalano 2. Re: Bizarre Multiple Catastrophic Truss Failure - Limited Permission to reprodu by "Hall, Delbert L." 3. Re: Bizarre Multiple Catastrophic Truss Failure - Limited Permission to rep by usctd [at] columbia.sc 4. Re: Bizarre Multiple Catastrophic Truss Failure - Limited Permission to rep by "Hall, Delbert L." 5. Re: DMX512 Back Channel by Jerry Durand 6. The twist in the truss by kim.hartshorn [at] plattsburgh.edu 7. Re: The twist in the truss by Jerry Durand 8. Re: Bizarre Multiple Catastrophic Truss Failure / rfc (long) by Dale Farmer 9. Taxidermy needed by Jim Ream 10. Re: Taxidermy needed by "Andrew Vance" 11. Re: Bizarre Multiple Catastrophic Truss Failure - Limited Permission to repr by Bill Sapsis 12. Re: Taxidermy needed by Pat Kight 13. Re: Bizarre Multiple Catastrophic Truss Failure / more pix, second look (long) by "Cyr, Dale" 14. Re: Bizarre Multiple Catastrophic Truss Failure / more pix, second look (long) by "Steven Haworth" 15. Re: Bizarre Multiple Catastrophic Truss Failure - Limited Permission to repro by David Marks 16. Re: Bizarre Multiple Catastrophic Truss Failure / more pix, second look (long) by "Cyr, Dale" 17. Re: Bizarre Multiple Catastrophic Truss Failure / more pix, second look (long) by Richard Niederberg 18. Position Available by "Stephen E. Rees" 19. Re: Bizarre Multiple Catastrophic Truss Failure / more pix, second look (long) by "Paul Schreiner" 20. cold water ground by b Ricie 21. Re: cold water ground by Dale Farmer 22. Re: Bizarre Multiple Catastrophic Truss Failure by Dorian Kelly *** Please update the subject line of your reply to use the subject *** line of the message you are replying to! Please only reply to *** one message subject in each reply. ---------------------------------------------------------------------- Date: Thu, 28 Oct 2004 07:55:35 -0400 From: Cosmo Catalano Subject: Re: Bizarre Multiple Catastrophic Truss Failure / rfc (long) In-reply-to: Message-id: <46DCA828-28D8-11D9-B433-000D936C1414 [at] williams.edu> References: Thanks, Dale for your willingness to share info about this incident. In regards to the torsion question, nearly all long, relatively slender (narrow) beams will have a rotational component in their failure mode as the top of the beam is compressed and buckles sideways under loads. The distance between bracing distance is one of the factors necessary for complete beam design. In floors, this is usually taken care of by what ever decking system is used as well as bridging or cross bracing at specified intervals. I suspect in a free hanging box truss, much of this lateral flexing is countered by the geometry of the truss. In triangular truss, there is much less resistance to buckling of the compression chord--especially if it is hung point up with only the single member resisting compression forces. I'm surprised that the manufacturer permitted this configuration for long spans. I'm glad no one was hurt. This is an excellent real life lesson on how things can fail in somewhat unexpected or non-intuitive ways. Thanks again for sharing this info. Cosmo Cosmo Catalano Production Manager Williams College Dept. of Theatre 1000 Main St. Williamstown, MA 01267 ------------------------------ Subject: RE: Bizarre Multiple Catastrophic Truss Failure - Limited Permission to reproduce Date: Thu, 28 Oct 2004 08:27:24 -0400 Message-ID: From: "Hall, Delbert L." Patrick asked: 1. According to the first posting from Dale, the motor points were 18"=20 from the ends of the truss, putting them about 62' from each other. If=20 it's not possible to get a middle point for lack of motors, is it possible=20 to put the two motors closer to the 'quarter-points' (the two points=20 approximately 1/4 of the length of the truss in from the ends)? Wouldn't be=20 better, Bill S. and Delbert, for an evenly distributed load? Or, Dale, are=20 your pick points in the roof(?) that far apart? It would lessen the span to=20 about 30' - 35'. (I could be all wrong on this - Bill? Delbert? - I don't=20 do many trusses, but I DO do a lot of beams.) Delbert's Responds: First, a truss is a type of beam and the same rules apply to both, Next, yes it would be better to move the pick points inward to reduce the span of the beam (truss). This will create what is called a two-point cantilever beam load. A cantilevered load puts a lot of stress on the beam. Harry Donovan's book has a lot of good information on calculating beam loads. The question of how far to move the points depends on the distribution of the load, but I would say that a good general rule for an evenly distributed load might be to move the points so that no more than 20% of the total length of the truss is cantilevered on each side and no less than 60% of the total length of the truss is between the pick points. Your 25% rules may also be acceptable; I have just always used 20%. BIG NOTE: The 20% rule is just MY generalization based on MY experience and is not based on real calculations of loads. I welcome better advice from people with more experience on this subject (and there are a lot) than me. Following my rule above, (for a 65' truss) the pick points would be 13 feet from the ends of the truss and the center span would be 39 feet. =20 -Delbert ------------------------------ Message-ID: <1357.129.252.241.105.1098968654.squirrel [at] webmail.columbia.sc> In-Reply-To: References: Date: Thu, 28 Oct 2004 09:04:14 -0400 (EDT) Subject: Re: Bizarre Multiple Catastrophic Truss Failure - Limited Permission to reproduce From: usctd [at] columbia.sc I don't use truss much anymore, but I cannot remember ever seeing a truss hung with what I consider such a severe cantilever. This means that the end 10' sections are only supported at one end. Is truss meant to be used like this? How do you figure what those end pieces of truss can actually support given the load table the manufacturer provides? Perhaps I am missing something here. -- Eric Rouse TD-University of SC, Columbia Freelance Foyboy > For info, archives & UNSUBSCRIBE, see > --------------------------------------------------- > > Patrick asked: > > 1. According to the first posting from Dale, the motor points were > 18" > from the ends of the truss, putting them about 62' from each other. If > it's not possible to get a middle point for lack of motors, is it > possible > to put the two motors closer to the 'quarter-points' (the two points > approximately 1/4 of the length of the truss in from the ends)? Wouldn't > be > better, Bill S. and Delbert, for an evenly distributed load? Or, Dale, > are > your pick points in the roof(?) that far apart? It would lessen the span > to > about 30' - 35'. (I could be all wrong on this - Bill? Delbert? - I > don't > do many trusses, but I DO do a lot of beams.) > > Delbert's Responds: > > First, a truss is a type of beam and the same rules apply to both, Next, > yes it would be better to move the pick points inward to reduce the span > of the beam (truss). This will create what is called a two-point > cantilever beam load. A cantilevered load puts a lot of stress on the > beam. Harry Donovan's book has a lot of good information on calculating > beam loads. The question of how far to move the points depends on the > distribution of the load, but I would say that a good general rule for > an evenly distributed load might be to move the points so that no more > than 20% of the total length of the truss is cantilevered on each side > and no less than 60% of the total length of the truss is between the > pick points. Your 25% rules may also be acceptable; I have just always > used 20%. BIG NOTE: The 20% rule is just MY generalization based on MY > experience and is not based on real calculations of loads. I welcome > better advice from people with more experience on this subject (and > there are a lot) than me. > > Following my rule above, (for a 65' truss) the pick points would be 13 > feet from the ends of the truss and the center span would be 39 feet. > > -Delbert > ------------------------------ Subject: RE: Bizarre Multiple Catastrophic Truss Failure - Limited Permission to reproduce Date: Thu, 28 Oct 2004 10:36:20 -0400 Message-ID: From: "Hall, Delbert L." Eric, You are correct that 13 feet is a pretty long cantilever, I based this on the fact that Dale said that the manufacturer OKed this truss to span 50 feet between supports. Personally, I think that this is way too far and the truss needed at least three pick points. As it turned out, they tried to stretch that span to 62 feet and the truss failed. =20 The BIG unknown in my earlier post was the unstated load on the truss. That will be a big determining factor as to how far you can cantilever the truss. This is what technical support is for. If you are not sure about a situation, call the company, ask them to run the numbers and OK the setup before you put it up. -Delbert Delbert L. Hall, President Hall Associates, Inc. Phone: 423-773-HALL Web: www.flyingfx.com -----Original Message----- From: Stagecraft [mailto:stagecraft [at] theatrical.net] On Behalf Of usctd [at] columbia.sc Sent: Thursday, October 28, 2004 9:04 AM To: Stagecraft Subject: Re: Bizarre Multiple Catastrophic Truss Failure - Limited Permission to reproduce For info, archives & UNSUBSCRIBE, see --------------------------------------------------- I don't use truss much anymore, but I cannot remember ever seeing a truss hung with what I consider such a severe cantilever. This means that the end 10' sections are only supported at one end. Is truss meant to be used like this? How do you figure what those end pieces of truss can actually support given the load table the manufacturer provides? Perhaps I am missing something here. --=20 Eric Rouse TD-University of SC, Columbia Freelance Foyboy > For info, archives & UNSUBSCRIBE, see > --------------------------------------------------- > > Patrick asked: > > 1. According to the first posting from Dale, the motor points were > 18" > from the ends of the truss, putting them about 62' from each other. If > it's not possible to get a middle point for lack of motors, is it > possible > to put the two motors closer to the 'quarter-points' (the two points > approximately 1/4 of the length of the truss in from the ends)? Wouldn't > be > better, Bill S. and Delbert, for an evenly distributed load? Or, Dale, > are > your pick points in the roof(?) that far apart? It would lessen the span > to > about 30' - 35'. (I could be all wrong on this - Bill? Delbert? - I > don't > do many trusses, but I DO do a lot of beams.) > > Delbert's Responds: > > First, a truss is a type of beam and the same rules apply to both, Next, > yes it would be better to move the pick points inward to reduce the span > of the beam (truss). This will create what is called a two-point > cantilever beam load. A cantilevered load puts a lot of stress on the > beam. Harry Donovan's book has a lot of good information on calculating > beam loads. The question of how far to move the points depends on the > distribution of the load, but I would say that a good general rule for > an evenly distributed load might be to move the points so that no more > than 20% of the total length of the truss is cantilevered on each side > and no less than 60% of the total length of the truss is between the > pick points. Your 25% rules may also be acceptable; I have just always > used 20%. BIG NOTE: The 20% rule is just MY generalization based on MY > experience and is not based on real calculations of loads. I welcome > better advice from people with more experience on this subject (and > there are a lot) than me. > > Following my rule above, (for a 65' truss) the pick points would be 13 > feet from the ends of the truss and the center span would be 39 feet. > > -Delbert > ------------------------------ Message-Id: <6.1.2.0.0.20041028081442.0256b6a0 [at] localhost> Date: Thu, 28 Oct 2004 08:19:57 -0700 From: Jerry Durand Subject: Re: DMX512 Back Channel In-Reply-To: References: At 08:42 PM 10/27/2004, you wrote: >Several companies do use the second pair for various legitimate functions >which may be proprietary, but are not always. Some companies do not wire >pins 4 & 5 at all, some wire them through. You will have to check with >the manufacturer directly or through their documentation. This ambiguity >is addressed in the new ANSI version of the standard developed though the >ESTA Technical Standards Program. It is expected to be published >soon. Compliant legacy equipment should have no problem working with >products compliant with the new version and vice-versa. Again - see the >link above. It should answer most questions. Even if the new version spells out what is on that second pair, I'm not convinced I should provide any support for it in future equipment. Since I have NO control over what our boxes have to co-exist with there's no way I could know in advance if I need to supply power, use power, supply or monitor data transmissions (and what format the data is in). For example, with something as "simple" as a DMX isolator box the first channel is easy (RS-485 to opto-isolator to RS-485). How would you propose to support the second channel? ---------- Jerry Durand Durand Interstellar, Inc. 219 Oak Wood Way Los Gatos, California 95032-2523 USA tel: +1 408 356-3886 fax: +1 408 356-4659 web: www.interstellar.com ------------------------------ Message-ID: <1098976390.41810c8629e7c [at] webmail.plattsburgh.edu> Date: Thu, 28 Oct 2004 11:13:10 -0400 From: kim.hartshorn [at] plattsburgh.edu Subject: The twist in the truss Hey all if this truss was rigged with the curtain tied to the top chord and draped over the downstage bottom cord and just allowed to settle...well the weight of the curtain would pull that top chord to the bottom. the only thing resisting this tendancy was the choke and wrap 18" from either end of a 65' span..this would result in a temendous twisting force over the length of the span...additionally i think this force would be in opposition at the 5' section...both ends of the 5'section would be attempting to twist in the direction opposite of it's center. mixing the sections randomly over 30 installations would have averaged out all the stresses...installing them randomly in order and also randomly end for end it would make a certain ammount of sense that both trusses reached the same point of metal fatigue at the same time...the story of the Comet Jetliners is appropriate...they started falling out of the sky within months of each other. although it seems like just looking at a 65' span with two picks would be difficult to do without thinking in your head that there ought to be a center pick i am betting that the practice of tieing off the goods to the top chord is what actually did in the truss. glad noone was injured Kim Hartshorn ------------------------------ Message-Id: <6.1.2.0.0.20041028083202.025b3860 [at] localhost> Date: Thu, 28 Oct 2004 08:38:06 -0700 From: Jerry Durand Subject: Re: The twist in the truss In-Reply-To: References: At 08:13 AM 10/28/2004, you wrote: >mixing the sections randomly over 30 installations would have averaged out >all >the stresses...installing them randomly in order and also randomly end for >end >it would make a certain ammount of sense that both trusses reached the same >point of metal fatigue at the same time...the story of the Comet Jetliners is >appropriate...they started falling out of the sky within months of each other. Also remember that while the other sections were mixed as to position, the 5' sections were ALWAYS in the center, so the only randomness with them is end-for end. That would explain them both failing together (I will assume the welds were done robotically* so they would all be identically good or bad). *I assume robotic welds because that's the easiest way to maintain consistent quality (ISO standards aren't as concerned about high quality, just consistent quality). Also, unless this truss is made off-shore, robot welders are cheaper than a large team of certified welders. Of course, the truss could be from a small company with one guy welding them in his garage, if that's the case all bets are off. ---------- Jerry Durand Durand Interstellar, Inc. 219 Oak Wood Way Los Gatos, California 95032-2523 USA tel: +1 408 356-3886 fax: +1 408 356-4659 web: www.interstellar.com ------------------------------ Message-ID: <418122C1.77F922D0 [at] cybercom.net> Date: Thu, 28 Oct 2004 12:48:01 -0400 From: Dale Farmer Subject: Re: Bizarre Multiple Catastrophic Truss Failure / rfc (long) References: Bill Sapsis wrote: > For info, archives & UNSUBSCRIBE, see > --------------------------------------------------- > > on 10/27/04 11:09 AM, Noah Price at stagecraft-web [at] theprices.net wrote: > > > For info, archives & UNSUBSCRIBE, see > > --------------------------------------------------- > > > > > > On Oct 27, 2004, at 2:00 AM, Cyr, Dale wrote: > > > >> noah has graciously agreed to host several high resolution photos > >> of the broken pieces, and hopefully he will respond to this thread > >> with a url. > > > > > > > > > Thanks Noah. Yeah. Looks like the truss wasn't supported against rotation > and that's what it did. a 65' span is a long way to go without pick up > points. > > This is why I always use 2 slings. You maintain much better control that > way. And yeah, 65' is a long way to go. That much fabric weighs a lot more > than some folks anticipate. A center motor would have helped a lot. > > Bill S. I see in the picture Broken left side close up, what looks like a crack in the weld. That darker area may be corrosion from exposed metal in the crack. That may have been where the failure started, but when you had the same failure two times in a row, that leads me to look at the design of the load. The picture Broken left side connector plate on the second page has some black stuff where I expect to see broken weld metal, so that is something to look at in a better light. The data plate said a 50 foot span was only good for 1027 pounds evenly distributed. Off the top of the head guess is that the 60 foot span weight would only be around 600 lbs. What was the dry weight of the curtain with chains and everything? Adding in some jerking of the load and a twisting of that long a lever on the thing, I'd also look into the rental history of the truss. Date of manufacture was 1999, so it's been around a while. Please keep us informed about further results of the investigation. --Dale ------------------------------ In-Reply-To: References: Message-Id: From: Jim Ream Subject: Taxidermy needed Date: Thu, 28 Oct 2004 11:38:35 -0500 The University of Indianapolis is working on a production of Endgame. As part of the director's/designers concept, we are searching for taxidermy. We are specifically looking for full bodies of animals and birds and hope to avoid mounted heads, fish etc. If you have any creatures sitting around your attic or prop room and would be willing to sell or loan them, please contact us off line. Thanks, Jim Ream ream [at] uindy.edu or Jeffrey Barnes jbarnes [at] uindy..edu ------------------------------ Message-ID: <03bf01c4bd12$dfad6400$0500000a [at] anneb> From: "Andrew Vance" Cc: ream [at] unindy.edu, jbarnes [at] unindy.edu References: Subject: Re: Taxidermy needed Date: Thu, 28 Oct 2004 12:22:55 -0500 > The University of Indianapolis is working on a production of Endgame. = > As part of the director's/designers concept, we are searching for=20 > taxidermy.=20 When I did "Mousetrap" in undergrad, we had a large slew of taxidermic = animals [some mounted heads and some not] adorning the walls, bookcase, = nooks and crannies of Monkswell Manor. All of our animals except the = moose head came from the university's Biology Department: wolves, = coyotes, small mammals, birds, etc. They had an impressive stock and = were willing to work with us as to which pieces we'd like and which they = would let out. Might be worth it to check if your Bio department has a = stock and is willing to lend you some. -- Sincerely, Andrew Vance Lighting Designer/Supervisor Omaha Theatre Company/Omaha Theatre Ballet ------------------------------ Date: Thu, 28 Oct 2004 13:34:51 -0400 Subject: Re: Bizarre Multiple Catastrophic Truss Failure - Limited Permission to reproduce From: Bill Sapsis Message-ID: In-Reply-To: on 10/28/04 9:04 AM, usctd [at] columbia.sc at usctd [at] columbia.sc wrote: > I don't use truss much anymore, but I cannot remember ever seeing a truss > hung with what I consider such a severe cantilever. This means that the > end 10' sections are only supported at one end. Is truss meant to be used > like this? How do you figure what those end pieces of truss can actually > support given the load table the manufacturer provides? When looking at cantilevers it's important to remember that you never, ever place a connection point (the place where two sections of truss are joined) on the offstage (or outside) end of the rig. A pick up point HAS to support that connection regardless of whether it's a bolt plate, spigoted or bubble gum connection. Bill S. www.sapsis-rigging.com 800.727.7471 800.292.3851 fax 267.278.4561 mobile We stand behind, and under, our work. ------------------------------ Message-ID: <41812F4A.4060705 [at] peak.org> Date: Thu, 28 Oct 2004 10:41:30 -0700 From: Pat Kight Subject: Re: Taxidermy needed References: In-Reply-To: Jim Ream wrote: > The University of Indianapolis is working on a production of Endgame. > As part of the director's/designers concept, we are searching for > taxidermy. We are specifically looking for full bodies of animals and > birds and hope to avoid mounted heads, fish etc. If you have any > creatures sitting around your attic or prop room and would be willing to > sell or loan them, please contact us off line. Pardon if this is too obvious or you've already done it, but have you checked the phone book for a taxidermist near you? With the right sort of gentle arm-twisting (and perhaps a prominent ad in the program) you might be able to convince them to provide everything you need. We've worked with a local taxidermist on and off over the years, and found them very helpful. Like many non-theatrical businesses, they get intrigued by the unusual needs we have and seem to enjoy the challenge of meeting them. -- Pat Kight Albany (Ore.) Civic Theater kightp [at] peak.org ------------------------------ Subject: RE: Bizarre Multiple Catastrophic Truss Failure / more pix, second look (long) Date: Thu, 28 Oct 2004 11:24:56 -0700 Message-ID: <407DF7D68DD30440B5CEB70ED234D1CF0316E245 [at] excuswa100.americas.unity> From: "Cyr, Dale" to all: I took more pix and noah posted them at: Limited permission to reproduce, as noted ealier, is extended to these photos. I looked at two areas specifically: 1. evidence of torsional force there are 20 sections of 10' truss altogether and 3 sections of 5' truss. 12 of the 10' sections were involved, 2 of the 5' sections were involved. the truss was purchased by the house, and never rented out. however, the house maintainance crew (not IA) have (alledgedly) installed the truss several times on their own. we have kept the truss sections separated since the incident. so, we took all of the truss section that were NOT involved in the incident, and layed them out on the floor. all of them were moved around on the floor to eliminate variations in the floor itself. all sections show torsional force past the yeild point, as evidenced by the fact that they "rock" when placed on a flat surface. see the new photo. I didn't have a tape with me, so I placed a 9v battery on the floor for reference. this is the most extreme example of its kind, and was actually taken from a section that *was* involved in the incident. but *all* (except one) sections, including those not involved, show this deformation to some degree. most show a twist of about 1/8 to 1/4 inch over the 10' length. several of the truss, including those not involved, show slight deformation of the top chord. by this I mean a slight bowing, or bending, not kinking. none of the people who regularly handle this truss are aware of the significance of this, or if they are, they attributed the slight rocking motion to an uneven floor. it turns out that the truss sections were manufactured in different years. 18 sections of the 10' and 1 of the 5' sections were manufactured in aug 1995; 2 of the 10' sections and 2 of the 5' sections were manufactured in june of 1999. the manufacturer changed their name (slightly) during this interval. the manufacturer states that their design factor is 2:1. the sections that failed are the 2 more recently made 5' sections. *********************************************************** 2. weld separation I closely inspected the welds of every section of truss under good light. I didn't find any visual evidence of cracking, deteriorization, or separation. I did notice several welds, all on the new pieces, that seemed, in my unprofessional and inexperienced estimation,=20 to be sitting "on top of" the truss members, as opposed to fully engaging both the connector plate and truss member. noah has graciously agreed to post even more pix of these. the pix titled "broken left side weld" shows that, in this instance anyway, the weld itself separated. the weld did not separate from the truss member, and the truss member itself did not tear; the weld separated along its own run. the pix titled "broken left side close up" shows this clearly. this pix also shows evidence of what I'm calling "sitting on top of" the member, as opposed to fully engaging it. (I think somebody ealier called this a "cold weld".) the pix titled "broken left side connector plate" also clearly shows a lack of weld penetration into the connector plate. the entire face of the connector plate is visible between the welds. this is opposed to the pix on page 2, "broken member (not weld)", which clearly shows that the weld held, and in fact ripped a portion of=20 the truss member away. *********************************************************** 3. (I know I said 2; this is in response to other posters regarding load :) the total load is approx 600#, and as noted by myself and others, NOT uniformly distributed, due to the tapering to accommadate the seats. the manufacturer was consulted regarding the pick points and the load distribution, and when asked "will it hold?" their comment was, "well, we wouldn't recommend it". it is on the outer edge of their spec. the reasons a third motor was not used are: the 2 motor config, although at the end of the allowable spec, seemed to be inside the spec; (the math is very compliated due to the continuous changing load over the length) the place for a 3rd motor is very problematic, difficult to get to, in the way of the lights. cost... the building was attempting to manage cost by not overbuilding, but not underbuilding either. a cantelevered arrangement might be possible, but the math most definitely must be done. (I have all the formulas, having taken donovan's class, but again, it's a continously=20 changing load, not multiple points, I was out of the country at the time of design and install, and endpoints seemed a more known quantity to those involved at the time.) (not excuses; just an explanation of why it was done the way it was done.) and as bill noted, the last joined connector plates must be supported, not necessarily by a motor directly overhead, but at least by a "reverse bridle". (which of course will introduce more compression in the truss.) *********************************************************** I *think* I've answered everyones questions; if not please repeat them. question to y'all: the question was posed to me: what does a failure look like? iow, as I approach the failure point, what happens? does aluminum truss "bend"? "kink"? "tear"? "explode"? and are the details in the photos consistant with an overload condition? or was something else going on here? why, with a 2:1 design factor, did both sides fail within an hour of each other? surely there is something going on here besides the laws of averages building up and colliding together on the same morning... the only difference from the way "it's always been done" ;),=20 is the way the spansets were rigged. but the truss didn't fail in a way that I would expect,=20 if it was caused by the spansets... proposal: the house and the installation contractor are not interested in paying for a formal structural analysis of the failed sections or the remaining sections. they will just be replaced. but they would pay for shipping to someone on this list who is interested in taking this on as class project in a educational institution, the only condition being that the results must be reported to this list. dale cyr Training Supervisor IATSE Local 93 Spokane Wa ------------------------------ Subject: RE: Bizarre Multiple Catastrophic Truss Failure / more pix, second look (long) Date: Thu, 28 Oct 2004 13:43:58 -0500 Message-ID: <721DC9EE550F834A92EC08BDC332B0EE01608305 [at] trader.river.idm.com> From: "Steven Haworth" Let me ask what may be a dumb question... If the truss was hung point-down, and the load attached to the bottom, = would the failure have still happened? This would eliminate the = twisting moment, wouldn't it? There's still the weight issue - on the = edge of the spec, but it seems the twist did most of the damage. PS - Seems an undergrad-level civil engineering course could have a lot = of fun analyzing this. - Steven (sjh [at] idm.com) --------------------------- http://www.stagelights.info ------------------------------ Message-ID: <4181425E.7030100 [at] davidmarks.cc> Date: Thu, 28 Oct 2004 15:02:54 -0400 From: David Marks Subject: Re: Bizarre Multiple Catastrophic Truss Failure - Limited Permission to reproduce References: Bill Sapsis wrote: >When looking at cantilevers it's important to remember that you never, ever place a connection point (the place where two sections of truss are joined)on the offstage (or outside) end of the rig. > Bill, For the enlightenment of us sound guys: Another way to state this is: A connection point must always be inside 2 pick points. Is this correct? My question is: If you have a tough decision because of building structure, are you better picking up on a long truss, rather than the 5 foot connecting section being discussed here, or is that issue moot assuming all connections are solid and bolted properly? Thanks, this has been a very interesting thread. Dave Marks church sound/video guy ------------------------------ Subject: RE: Bizarre Multiple Catastrophic Truss Failure / more pix, second look (long) Date: Thu, 28 Oct 2004 12:24:43 -0700 Message-ID: <407DF7D68DD30440B5CEB70ED234D1CF0316E247 [at] excuswa100.americas.unity> From: "Cyr, Dale" steven: I don't believe the failure would still have happened. if hung point down, the spansets would have been rigged normally, and curtain would have been hung from the bottom cord. I think this is what will be done in the future, with a small valence curtain to hide the truss if it is really that objectionable. if I was teaching an undergrad level engineering course, I'd salivate at the chance to analyze a real world=20 semi-mysterious multiple catastrophic truss failure, for merely the cost of posting the results :) (but since I don't teach that, I'd like to *take* that class :) dale cyr Training Supervisor IATSE Local 93 Spokane Wa -----Original Message----- From: Stagecraft [mailto:stagecraft [at] theatrical.net] On Behalf Of Steven Haworth Sent: Thursday, October 28, 2004 11:44 AM To: Stagecraft Subject: Re: Bizarre Multiple Catastrophic Truss Failure / more pix, second look (long) For info, archives & UNSUBSCRIBE, see --------------------------------------------------- Let me ask what may be a dumb question... If the truss was hung point-down, and the load attached to the bottom, would the failure have still happened? This would eliminate the twisting moment, wouldn't it? There's still the weight issue - on the edge of the spec, but it seems the twist did most of the damage. PS - Seems an undergrad-level civil engineering course could have a lot of fun analyzing this. - Steven (sjh [at] idm.com) --------------------------- http://www.stagelights.info ------------------------------ Date: Thu, 28 Oct 2004 12:30:38 -0700 Subject: Re: Bizarre Multiple Catastrophic Truss Failure / more pix, second look (long) Message-ID: <20041028.123043.2472.1.ladesigners [at] juno.com> From: Richard Niederberg Dear Dale, Thank You for leading by example, and demonstrating how these matters should be investigated openly, with this opportunity for a professional comment period. You have performed a public service. And, thank you, Noah, for providing space on your website. 'A picture is worth a thousand words', as they say... /s/ Richard > Dale Cyr writes: > to all: > I took more pix and noah posted them at: > > Limited permission to reproduce, as noted ealier, is > extended to these photos. ________________________________________________________________ Speed up your surfing with Juno SpeedBand. Now includes pop-up blocker! Only $14.95/ month - visit http://www.juno.com/surf to sign up today! ------------------------------ Message-ID: <418185DD.3060001 [at] fredonia.edu> Date: Thu, 28 Oct 2004 19:50:53 -0400 From: "Stephen E. Rees" Subject: Position Available Hi Folks, One of our dance professors is retiring after over 30 years and a search for a replacement has commenced. Should you have any dance colleagues who are in the market for Fall 2005, suggest that they look at: www.fredonia.edu/humanresources/jobs/dance.htm Please don't contact me, I'm not even on the search committee. Thanks for the bandwidth. Regards, Steve Rees, TD SUNY-Fredonia ------------------------------ Subject: RE: Bizarre Multiple Catastrophic Truss Failure / more pix, second look (long) Date: Thu, 28 Oct 2004 21:48:14 -0400 Message-ID: <6E497ADB607656479C24E6D7BF6B505A74AD36 [at] exchange.rmwc.edu> From: "Paul Schreiner" > the question was posed to me: what does a failure look like?=20 > iow, as I approach the failure point, what happens? does=20 > aluminum truss "bend"? "kink"? "tear"? "explode"? and are the=20 > details in the photos consistant with an overload condition?=20 > or was something else going on here? Again, small disclaimer: I do not have nearly as much experience with aluminum as I'd like, so take this with the proverbial grain. That being said, a good weld (in my experience) will tear out the material to which it is welded. The alloy that results in the weld pool is generally stronger than the "pure" material on either side. At the same time, the material used in the welding process is generally harder and more brittle than both the material being welded and the resultant alloy, so a poor weld will (a) break along the bead before damage to the other material occurs and (b) have a lower breaking strength than a good weld. It'll also resist dynamic loads a lot less because of the brittleness factor. If the WLL of the truss was calculated by assuming good welds all along the piece, then the WLL of the truss pieces that appear to have seriously substandard unpenetrating welds would be significantly lower. How much lower would pretty much be impossible to reliably determine without destructive testing. Figuring 21 oz. velour for the material at 50% fullness, and using the original estimated dimensions (65' wide, short height of 15' and a long side of 45'), I come up with approximately a 450# load on each truss. Since a uniformly distributed load over a 50' span carries a specified 1027# WLL (and by looking at the other numbers as well) I'd go out on a limb and say that a 60' span could "probably" carry about 750#; a 70' span would then be pushing down near 450#. Ballpark a 600# limit for a 65' span (I know, it was 62' between points) with good welds, and then factor in the poor welding, and I'd say this was beyond the capabilities of the truss--especially since it wasn't a uniform load (note that center point loads are about 50% of the uniform WLL). > why, with a 2:1 design factor, did both sides fail within an=20 > hour of each other? surely there is something going on here=20 > besides the laws of averages building up and colliding=20 > together on the same morning... Just as a totally personal comment, if I knew I had a piece rated at a certain amount but only using a design factor of 2:1, I wouldn't come near the weighted rating...I prefer 5:1 as a minimum. Here's the wild card in all of this...no one has yet mentioned the fact that repeated positioning of the curtain while the whole thing was in the air would put a much higher load on the truss because it's now a dynamic load rather than static; and it would follow that the onstage dynamic torque would be much greater, and result in an even higher degree of twisting, than the offstage (and both more than the static torque). It's possible that the motors were working too fast and accelerating the truss from a dead stop too quickly for the truss to handle...and considering that one of the pieces failed during this leveling process raised an eyebrow to say the least. The simulataneousness of the timing may have been related to the humidity, but it would have happened sooner or later. Of that I have no doubt. > the only difference from the way "it's always been done" ;),=20 > is the way the spansets were rigged. > but the truss didn't fail in a way that I would expect,=20 > if it was caused by the spansets... If two spansets were set in opposition at each point, then the spansets shouldn't be considered to be the fault here most likely. After reading what you wrote about the twisting, I'd be leaning towards pointing fingers at the way the curtains were hung off the top cord and draped over one side (thereby placing uneven torque on the truss, less offstage than onstage); the distance of the span being beyond the recommended manufacturer's limit; the apparent welding deficiencies; and the randomness in which the truss was assembled (with the resultant randomness in twists and stresses down the length of the assembled sections) as the major factors. In that order. And the standard disclaimers apply...especially cuz I'll be the first to admit I'm not an expert on truss nor physics. I just have a pretty good grasp of the concepts, even if my terminology is a little suspect ;) ------------------------------ Message-ID: <20041029033040.35466.qmail [at] web50607.mail.yahoo.com> Date: Thu, 28 Oct 2004 20:30:40 -0700 (PDT) From: b Ricie Subject: cold water ground In-Reply-To: Can someone explain cold water ground to me and how it helps alleviate hum in sound? ===== Brian Rice b_ricie [at] yahoo.com __________________________________ Do you Yahoo!? Yahoo! Mail - You care about security. So do we. http://promotions.yahoo.com/new_mail ------------------------------ Message-ID: <4181C08B.82A94BB5 [at] cybercom.net> Date: Fri, 29 Oct 2004 00:01:15 -0400 From: Dale Farmer Subject: Re: cold water ground References: b Ricie wrote: > For info, archives & UNSUBSCRIBE, see > --------------------------------------------------- > > Can someone explain cold water ground to me and how it > helps alleviate hum in sound? Grounding in audio systems is a thick chapter in the books. Cold water ground, without any context, could mean a couple of different things, now mostly obsolete. Cold water piping as a good ground system have been deprecated, due to the growing use of plastic pipes in water systems. The bottom line is that you want all the grounds in the audio system to come from one single common electrical connection to the earth, and with low enough resistance in all your ground conductors that there is no momentary differences in the ground reference in different points in your system. This keeps additional current from the ground conductors from getting into your signal paths, which makes noise. This is, of course, a vast oversimplification with lots of hand waving of the details. --Dale ------------------------------ Message-Id: In-Reply-To: Date: Fri, 29 Oct 2004 09:28:41 +0100 From: Dorian Kelly Subject: Re: Bizarre Multiple Catastrophic Truss Failure I am not a rigger, so I ask merely for information. Doe no one use bridles any more to create two pickup points out of one? Looking at the picture of the way that spansets are used to choke and wrap, which looks safe enough but is a sort of messy way to do it would it not make more sense to create a sort of spanset "spider" two main bridle arms each breaking out in to three sub arms to pick up each chord of the truss separately by means of a purpose made clips or clamps. This would absolutely prevent any rotational movement and also enable the currently cantilevered ends of the truss to be picked up properly Again apologies for ignorance from a non rigger ( but a reasonably experienced engineer) Dorian Kelly ------------------------------ End of Stagecraft Digest #178 *****************************