Tsm flying bridge

Brief

The aim of the game here is to rig a 7metre by 1metre bridge which is suspended 4 meters above the stage floor. During the course of this project I hope to illustrate how to suspend a bridge in the New Athenaeum theatre or indeed any theatre.

The Bridge Itself

The bridge could be made from many different materials, wood, steel, aluminum, titanium if you really wanted to. In this case it will be constructed from aluminum. It will be constructed in two sections each of 3.5metres by 1metre this is simply for the ease of construction and transportability. I was originally going to have the bridge made out of box steel but this material is a lot heavier then aluminum, so I went for the lighter option.

The look of this bridge is to be industrial like the bridges that use to be in factories. So it will keep its metal look and to hide the drifts they will be dressed with long link chain.

I know I am no an engineer but after a bit of research of gangways and access walkways this is how I think the bridge would be constructed

This picture shows how gangways for ships are constructed, depending on the designer the diagonal supports can be replaced but vertical ones. The hand rail will sit at a height of 1.5metres high.the floor will be covered with a 3mm aluminum sheet.

Rigging Equipment

I was having trouble calculating the exact weight of this bridge for 2 reasons.

I am no completely sure of how to construct the bridge, therefore how much aluminum would be required. Secondly how many people would be on this bridge at one time?

So for these reasons each of the 8 points suspending this bridge will take at least one tonne. You would think this would affect the cost of rigging by a fair wee whack but it doesn’t really. For example 5mm 7x7 wire core has a MBS(minimum breaking strain) of 1.62tonne costing (insert one I get a quote) compared to example 3mm 7x7 wire core has a MBS 0.58tonne costing (insert one I get a quote).

4 motor chain hoists- sm10 508V2-V capacity 500kg

8 lengths of 8 meter drifts, 5mm, 7x7 wire core, which have been threaded thru long link

2 lengths of 5 metre drifts 6mm 7x7 wire core

12 shackles at 1.50 tonne

6 shackles at 2 tonne

4 beam clamp at 1 tonne

4 clutch chain 2 tonne 3 metres in length

4 round slings 1 tonne at 1metres

2 two Leg Bridle 2 tonne 12mm 6x19 (thimble termination)

8 M20 eyebolts

Note motor chain hoists could be replaced with the academy’s new automated winches.

Rigging process

First things first is to get the hardware up to the grid. That is

4 motor chain hoists

4 beam clamps

4 clutch chains

4 round slings

The challenge here is getting the motors up to the grid. Easiest way to do this is to take the motors up the lift the prompt side fly floor then lower a line down the ladder and pull the motors up onto the grid. Once they are on the grid they will be put into position, the anchor points in at the grid are 500mm, 1800mm and 3100mm from the grids centre line. The motors will be at 1800mm from the centre line and will hang from the I beams via a 1tonne 1 meter strop. the power for the motors will come from the dimmer room were there is an free 200A supply, so cables will have to be ran from the grid down to the dimmer room on the prompt side fly floor. Once the motors are in place the two sections of the bridge will be bolted together. The sections will be held together with 6 bolts, M10, and nylon lock nuts. The eyebolts will be at 500mm, 1800mm and 3100mm from the centre point out.

The chains will be dropped down to deck level; thru the gaps were the pick ups for the bars run. once the chains hook is at working level the attached the hook to the 8m drift which has been dressed with the long link chain which in turn is shackled to the bridge via an eyebolt. This is repeated for each motor. Then the slack of the drifts is taken up but the bridge at this stage does not leave the deck. Now the hemp pick up lines would be dropped in for the drift pick ups. The hemp pick up the 5m drifts will be attached, and then the 8m drifts dressed in long link chain which is then attached to the master link of the bridle then the bridle legs shackle on to the eyebolts of the bridge. The slack is then taken up.

Now that the bridge is rigged up, let’s get this bad boy in the air. So, on the 4 motors we bring the bridge towards the grid, past the 4m mark so there is enough slack to rig the drift pick up lines so they can be attached to clutch chains on the grid. The clutch chain will be rigged onto the beam clamps on opposite sides. They will be joined together with a master link, which will sit above the desired position of the pick up which will be shackled onto the master link as well. Once the drift pick ups have been attached to there anchor points the 4 motors will be lowered until the drift lines take the weight of the bridge. A spotter must be used because if the motors lower too much past the fix picture up heights this will add more tension than they are meant to take!!!! Because the drift pick ups are a pacific size this should mean when they are all taking the tension of the bridge, the 4 motors should be all at the same height, in theory. If this is not the case it should be easy to see which motor needs to be lowered because the drift nearest that motor will have slack on it.

To make sure the bridge is completely level a sprit level can be used and by fine tuning the length of the chain hoists.

Accessing The Bridge

So to access this bridge we will have 2 steel deck platforms stage left and right. Because the platforms will have to reach a height of 4 meters the outriggers and treads will take up allot of space backstage. So I have opted to have 2 platforms, one at 2meters then one at 4. I have done this to reduce the size of treads needed to access the 4 meter platform. For this you will need:

4, 8x4 steel deck

8 lengths of 2metre scaf

8 lengths of 4 meter scaf

8 swivel clamps

16 footplates (8 of which will have half there base cut off so the plates will butt up nicely.

Rigging platforms

For the 2metre platform rigging is very simple. put in your 4, 2metre legs tighten the bolts and add your footplates.(make sure your half footplates are facing upstage) now have 2 people foot the legs as another 2 people lift the steel deck then start to walk it up.

For the 4metre platforms you could use the same technique as before but for the safety of your crew I wouldn’t, I would use a pulley to assist in the lift. To do this I would run a hemp line from the appropriate fly floor up to the grid, run it down to the deck, then back up to the grid then tied off at the fly floor. Thus creating a big loop basically. Attach a snatch block pulley onto the loop, then run another hemp line thru that pulley, this is the control line for the lift. Then by pulling on the hemp from the fly floor to the appropriate height in this case around 6 meter.

Once the platforms are in place screw down the footplates clamp the platforms together with swivel clamps, then add the outriggers and cross bracing. For this you will need:

Cross bracing

4 1.5 meter lengths of scaf

4 3 meter lengths of scaf

16 swivel clamps

Outriggers

2 1.5 meter lengths of scaf

2 3 meter lengths of scaf

4 swivel clamps

4 base plates

all scaf components are from stock

Masking

So since I'm not a designer I have opted for your basic stage masking for this project hard black masking. This could easily be changed for decorative flattage. The hard masking would make your basic boxed set with entrances at the bridge height with the steel deck platforms behind them so the performers have access to the bridge. Because of the height of the bridge the flats would have to be at least 7 meters in height so pickup lines from the grid would be used as well as bracing to hold them steady and in place.

Problems

The main problem I can see with this bridge is the fact if someone walks across it will want to sway. So to stop this swaying the bridge will be bolted to the steel deck platforms that provide the access to the bridge. The bracing of these platforms should provide enough force to stop any movement in the bridge.

Costings

hoist uk

4 motor chain hoists- sm10 508V2-V capacity 500kg cost

rope assemblies

8 lengths of 8 meter drifts, 5mm, 7x7 wire core, which have been threaded thru long link

2 lengths of 5 metre drifts 6mm 7x7 wire core

12 shackles at 1.50 tonne

6 shackles at 2 tonne

4 beam clamp at 1 tonne

4 clutch chain 2 tonne 3 metres in length

4 round slings 1 tonne at 1metres

2 two Leg Bridle 2 tonne 12mm 6x19 (thimble termination)

8 M20 eyebolts

Stage hire scotland

2 8x4 steel deck cost £30 per week

Scaf supplier

60 metre of scaf cost £109.76

Aluminium fot the bridge

www.ukaluminium.co.uk

28 sheets of alloy 1050 alumionium sheet 500mmx500mmx3mm cost £466.66

12 lenghts of alloy 6082 aluminium square tube size 1 3/4"x10SMGx1000m cost £144

12 leghts of alloy 6082 aluminium square tube size 1 3/4"x10SWGx2500mm cost £360

this is a rough costing more aluminium will probally be needed during the construction but this will give you a idea how much the bridge itself will cost with out the added costs of a structual engineer and fabricator.

still to add

costings once quotes come in