Controlling 8m column verticality & 8m tapered wall

[Galway11]

Hello everyone,

Have to set out 9m high columns in a couple of weeks for the first time!

Shutters will be prefabricated steel, +-3mm tolerance I think...

240 no. columns in a rectangular grid (150m x 70m), the grid is divided is divided by vertically tapered walls...so only two rows of columns can be seen at a time.

All on local grid coords, location not a problem but controlling verticality might be.

I don't think offset lines, sighting up and down with the EDM and measuring will be good enough or fast enough.

The engineer I took over from recommended setting up the EDM near the column and sighting up along two outside egdes until they agree with EDM crosshairs, doesn't sound good to me though.

I would probably use plumb bobs first. I was thinking of marking C/L offsets with the EDM, then using some form of vertical laser plummet and a target for precision and as a check. I have no experience with using lasers vertically...

Anyone have any experience of this?

Any thoughts on an 9m tapered wall from 1000mm to 500mm?

Would be grateful for any help as have to do it fairly soon!

 

[cherrypicker]

What specification are you working to?

The general method is to accurately set out and construct a "kicker" for each column (a starter shape of the concrete element about 100 to 150mm high). The shutters can be set to this kicker and kept vertical by plumb-bob. The concrete gang will make up a bracket that will simply clip over the shutter enabling it to be set vertical pre-pour and checked vertical after pour quickly.

As for the tapered wall, ask the concrete gang what lines they need and give it to them. Each point will still be based on horizontal and vertical linework to makeup triangulated dimensions.

In the UK we generally use NSCS and Section 7 details Construction Accuracy specifications. In 3rd Edition clause 7.8 describes Verticality of Elements but the Project Specification as Part 2 may specify different tolerances.

A modern instrument in good order and used correctly will measure angles and distances accurately. The instrument, however, has to be suitable for the task. Vertical control can be achieved with an instrument using different techniques (crosshairs or to a target) but the user should be confident that the results of any setting out will achieve the construction accuracy tolerances of the finished product.

If in any doubt, ask! The old saying "measure twice - cut once" is very apt. Good luck.

 

[Galway11]

Thanks for the reply.

Haven't seen any spec yet, just started! Floors going in at the minute, columns next couple weeks.

It's kickerless. Steel shutters have a notch for the column to receive precast panels with 10mm each side. As long as it works well they'll be happy...

 

[Galway11]

Thanks for the reply.

Haven't seen any spec yet, just started! Floors going in at the minute, columns next couple weeks.

It's kickerless. Steel shutters have a notch for the column to receive precast panels with 10mm each side. As long as it works well they'll be happy...

What is the best way exactly to check by EDM? Targets on the underside of the template for the plumb bobs might be a good idea. Setting up beneath to achieve a good face to sight to retro, but that depend on how good the template is fixed on I suppose...

Is simply sighting up along with the crosshairs good enough?

I'll need the luck I think I'm happier with things being closer to the ground!

 

[cherrypicker]

There must be a way of captivating the shutters during pours. If the shutters have a notch, then the installers will require these positions marked out. If ther are no kickers then is the column fixed by starter bars or dowel bars? or is there a recess in the floor to receive each column?

The use of an instrument is subject to many potential errors and it is the responsibility of the user to minimise each error. Therefore, there is no chance of EXACT measurements - only a very close approximation.

The installers will achieve very good accuracy with a plumb-bob when attached to a bracket on the outside of the shutter. One assumes the shutter is the same thickness throughout it's length so the offset dimension to the plumb-line should be similar top middle and bottom. Crosshairs could give very good results from an instrument in good order only if they are sighted parallel to element side.

In an as-built situation I have (had) fabricated a bracket to accurately coordinate three corners at three levels making 9 points on each column. The results can be mapped to check constructional accuracy for:
1. Size of Elements
2. Twist of Elements
3. Squareness of elements
4. Position on Plan
5. Verticality of Elements
6. Bow of Elements

Take care

 

[Galway11]

Cheers for replying,

The steel shutters are going to be fabricated specially for the job so they will have the notches already in.

I was talking to one of the chippies today and sounds like he plans to put a long spirit level up it! No mention of plumb bobs!

Think I have it sorted out...I have a local grid so I'll either give someone the prism or shoot to a retro at the top and I'll know how far along the grid east or north to move it...

The high walls all round won't help for sighting stations though.

Floor level slabs are poured without kickers, dowel bars or a recess to I don't know how they'll hold it at the bottom, hopefully they do. Only been on the job a few days.

Thought there would be a well established method for doing this with the EDM...

Using grid coords seems the simplest and fastest to me...sound good to you?


Cheers

 

[cherrypicker]

Keep us informed how you get on and what accuracies you are achieving in the final positions of elements.

 

[Zambo]

The first point is to cast the kicker accurately. Are you casting kickers? If not then you have to secure the column forms correctly, perhaps wedging off dowel bars.

I would use a spirit level for initial erection of the forms. Then plumb bobs to check before/after casting. A total Staion can then be used for an as-build survey.