concentrated load on old floor 2

[tchconsulting]

Hi, am looking for some advice concerning how to spread a concentrated load onto the ornately marble tiled floor of a ballroom in a Stately Home (it's an expensive floor!). The loading is from a tree (not a Christmas Tree ! ) which is to be temporarily erected on the floor for the purposes of filming a particular scene in a TV Drama. The tree weighs 4 tons. My initial thoughts are to use a steel I section, probable a 203/203/46UC seated on the floor and extending a width in the order of 4 metres to correspond with the spacing of the support beams beneath the floor. The concern I have is that there would still be a concentrated load beneath the center of the beam, as the beam attempts to defect under the load. Is there any easy way of determining the nature of support pressures beneath the spreader beam. Thanks, Tom

 

[Triangled]

If you can, it might be simpler to shore the floor from below. Otherwise you need to consider both strength and deflection.

 

[JAE]

Why don't you provide a gap between your spreader beams and the floor - and have the beam span across the slab area and rest on thicker plates positioned directly over the floor beams below?

That way, as the spreader beams are loaded they would deflect downward a known amount - but never touch the marble tile. And all the load would go directly onto the floor beams (through the tile in direct bearing) and this would minimize the flex in the floor slab - possibly minimizing stress in the tile.

There would still be deflection in the main floor beams and you would have to analyze those to see if their deflection would be within limits to avoid cracking the tile.

 

[a2mfk]

Hope you have a GREAT contract on this job stating NO GUARANTEES. There are TOO many unknowns when it comes to tile installation, and marble is especially brittle and poor in tension.

 

[tony1851]

How would you balance a tree on an 8" wide beam?

 

[msquared48]

Very carefully...

Mike McCann
MMC Engineering

 

[chicopee]

I am with Triangled as we used to do that when we rigged heavy machinery; and when we had multi floor below, we would shore all the floors below the heavy machinery that we moved on rollers.

 

[tony1851]

If it's an old Stately Home with a marble-floored ballroom, it's likely that the floor structure is built off heavy timber beams and finished in timber boarding, which then supports a bedding compound for the tiles.
If the steel beam was to be supported clear of the floor, spanning across two main beams, load will obviously be applied somewhere. Even if it could be shown that any existing main beams could support the load without undue deflection (whatever value is taken for that - who knows?), the bedding of the marble will be an unknown quantity.
Make sure your PI is up-to-date.

 

[tchconsulting]

Thanks to all for the comments, really useful in focusing my direction. Had already decided that propping the principal timber beams from beneath and raising the support structure a little above the floor, to cater for deflection of two UCs would be a way to go, however, as you have mentioned there are still unknowns, especially the uniformity of the bedding material between the top of a (presumed) timber floor structure and the tiles.
Also, the excess on my PI would be greater than the fee I would receive. Have decided therefore to say that I can provide a scheme such that the floor does not collapse, but that I an unable to guarantee that the marble tiles could not possible crack. Again, thanks.

 

[ameyerrenke]

Support it on a hovercraft. Sounds like your budget won't allow for that.

 

[a2mfk]

Very smart to make no guarantees about the floor, only certify the structure. Too many unknowns. Tile cracks for all kinds of reasons, and marble has pretty poor tensile strength and in my experience cracks fairly easily, especially if there are veins in the tile.