Overweight fly system

[ambientlight816]

I am doing a show that has an overweight batten... The arbor is at full capacity and my boss wants me to just hang a 50lb sandbag to the full arbor to make the weight even. Does anyone have anything showing that it's dangerous to do it that way? I need pictures and examples because her answer is always that "we don't need to follow those rules". This is at a highly popular college. There's an arbor capacity for a reason...

 

[DuckJordan]

Is there a placard with max weight per batten and system?

 

[ambientlight816]

Is there a placard with max weight per batten and system?

Yes. Overweight by 100lbs

 

[MPowers]

Do you have a free batten next to the over loaded
one? If so your safest and most judicious solution would be to marry the battens. The second best is the most obvious, find a way to trim some weight off the scenic unit. Not knowing what it is or how it is constructed, I can't comment on just how this might be done. If the batten is already over the system posted weight limit, the last thing you want to do is add counter weight. I gather that the need to balance is because the batten runs during the show???

 

[DuckJordan]

Then show him that and say the designer of the system specified that max was it. NO MORE! Have him give a call to any rigging company (specifically the one that installed yours) and have him ask if its okay to overload a batten.

 

[lwinters630]

You are right, the arbors are set to limit the load. To quote Wikipedia "Fly system infrastructure consists of the relatively permanent load-bearing and load-transferring structures of a stage house. The infrastructure, generally fabricated of structural steel members, is sized by a structural engineer during the design of a new theatre, or theatre renovation. Rigging system infrastructure ultimately limits a fly system's capacity." To know if you can add more weight, you must know the total load and how it is distributed. If a point load is on one cable past the loft block to the arbor, what is the safe working limit? In other words, there are specific limits on every component, from the bottom of the piece being flown along each pick point all the way to the arbor. I would suggest to first check the manufacture of the arbor system for the load limits. Then find the safe working limit based on your layout. If you or your boss do not know how to calculate this, bring in a professional rigger.

Ask this question, if this fails what will happen? That overweight load will come crashing down in about 4 seconds, accelerating at 32 ft/sec.

 

[cmckeeman]

Either split the load between two arbors, trim some weight off the batten, or find an alternate way of flying the scenery (truss and motors). If the system is already overloaded then you need to find a way to trim it, overloading it more or doing nothing is NEGLECT. If someone gets hurt from this then your boss could be found criminal negligent. If need be have her look at this thread, or contact an ETCP rigger in your area as to what she is opening herself to with overloading rigging.

Also how did you figure the system limit?

 

[BillConnerFASTC]

A lot to this but two essentials are design of the structural framing and the design of the rigging. There is no standard means of determining the design load of the structural framing. For the new build stages on which I consult I provide loading to the structural. I base it on every linsey that could be logically installed - even if some will not be initially - and all arbors full - an incredibly unlikely condition but for sure enough. We make sure that is posted because it is otherwise hard to find out. But others significantly derate or the designers have no idea what loads rigging imposes on structural framing.

I design a lineset based on batten length at 30 plf . That's from a kind of Broadway standard. That doesn't usually present much of a problem for basic or standard rigging hardware up to about 70 feet or so since common lofr blocks are usually rated for 500 or more, the entire lift line assembly usually much more than 500, but head blocks may be in the 2100 to 2200 pound range.

This is based on basic hardware from reputable major manufacturers.

That said, the best answer for the o.p. is to bring in a rigging contractor and have them replace the arbor if they agree its safe.

 

[StradivariusBone]

So if a lineset is listed at being rated to 1500 lbs and no other indication is given, does that imply the arbor weight can be 1500 lbs or the combined arbor and batten weight cannot exceed 1500 lbs?

 

[MichaelPHS]

Simplest answer of all, if you have to stop and think "is it safe to...." then it isn't. I, personally, would refuse and suggest another, safer way to do this as you have to think anything falling if it fails is gonna hurt. A lil science now;

An adult human skull can fracture with an impact force of 100 joules. 100 joules is represented by a mass of 1kg falling 10m, 5kg falling 2m or 10kg falling 1m. So, a lightweight lantern, like a PAR64 which weighs around 3kg, can fracture an adult skull on a drop of around 10 feet. In fact an adult skull will self-fracture when dropped around 4 feet. Figures for children's skulls are much lower.

And your saying she wants to add 50lb (for arguements sake 23kg actual 22.67kg if you care) to an already overloaded batten? The way I rig is via the old "Cirque" method. Never expect someone to walk under or use something that your not prepared to take the risk for yourself first. I know they use it for trapeeze's and the such but the principle still transfers

 

[Footer]

So if a lineset is listed at being rated to 1500 lbs and no other indication is given, does that imply the arbor weight can be 1500 lbs or the combined arbor and batten weight cannot exceed 1500 lbs?

No, any rigging systems max capacity is the weight that you can put on the pipe, not including pipe weight. This rule applies for single or double purchase systems.

 

[BillConnerFASTC]

So if a lineset is listed at being rated to 1500 lbs and no other indication is given, does that imply the arbor weight can be 1500 lbs or the combined arbor and batten weight cannot exceed 1500 lbs?

I'm less certain than Footer there is a universal standard for this. I alway think in terms of total load - batten and trim chains vs arbor and counterweight. You could use the tare weight - the amount of counterweight you can add on top of empty weight - but if you drop a batten and pick a piece on to lines, it's a lot more math. Designing for 30 PLF does compensate a little - because over 27 PLF is tare weight.

ETC's Prodigy marketing kind of made this an issue because they decided to include a best estimate of tare weight in the model name. Their 1000 model has 1000 pound capacity in an "average" application, but will lift 1200 pounds - of which the RACA and batten is a part. I find that more confusing and less helpful than just saying 1200 pounds, more like the other package hoist manufacturers have done.