supporting cantilever ends
supporting cantilever ends
(OP)
Would it hurt to support the open end corner of a 2-meter RC cantilever? Has someone tried it with an i-beam? How would you attach it to the rc cantilever open ends at the corner or sides (you can't put the i-beam in front because it will block the view of the store)?






RE: supporting cantilever ends
BA
RE: supporting cantilever ends
Please check attached picture. The cantilever is about 1.7 meters. How do you put i-beam in front so the weight of the cantilever can bear on the i-beam? The original plan was to just put hollow block at the side with tiny stiffener column, would this be load bearing enough to carry whatever is above the cantilever? The i-beam plan was just to lessen the load on the column holding the cantilever.
RE: supporting cantilever ends
Perhaps it would help for us to know how this came to be your problem.
... and what problem you are trying to solve.
Mike Halloran
Pembroke Pines, FL, USA
RE: supporting cantilever ends
RE: supporting cantilever ends
Mike, it's to be additional support to take some load off the main column because during seismic activity, cantilever are not good.
JAE, the top bars are composed of 4 pieces of 0.78 inch bars and bottom bars are 2 pieces of 0.78 inch bars so you right that a lone support could introduce positive bending.. that is why hollow blocks would be put in between. But hollow blocks are not load bearing.
If I add RC Wall in the section instead of stiffer column and hollow block. I wonder if anyone has tried this? My worry RC wall may have Torsions during seismic movement de-aligning it from the cantilever.
Can anyone think of other solutions?
RE: supporting cantilever ends
RE: supporting cantilever ends
RE: supporting cantilever ends
Do not forget that our buildings are designed for certain intensity of earthquakes, let's say magnitude 7.9 so if you can spend some more to make it survive magnitude 8.5. Why not. No buildings are designed for magnitude 11 because of costs.
Cantilever is one of the weakest links in an earthquake because it can act as pendulum.. so since the sides would be originally filled with hollow blocks and there is not much study about the load bearing and seismic performance of hollow blocks. I wonder if using RC walls would give the section more strength.
RE: supporting cantilever ends
it looks to me as though you've got a concrete pad (upper story floor ?) supported by concrete beams (along the perimeter); one of these edges (the street side ?) has what looks to be a small I beam "supporting" it. It looks to me as though theres a very convenient vertical wall that could support one side ?
but what do i know 'bout this stuff ??
Quando Omni Flunkus Moritati
RE: supporting cantilever ends
RE: supporting cantilever ends
My friend is the designer. He agrees cantilever are not good but we can't avoid it if clients want it. He said there is not much research about interactions of hollow blocks and frames so RC walls carrying the cantilever at the sides may not be bad if costs not issue.
Haven't you guys designed cantilever too? The load path of cantilever is not always good because it puts more stresses on the column.
rb, the piece is not an i-beam but a 4 piece 12mm bar where stiffer column will rise as well as hollow block. So I wonder what is the effect of replacing this with RC wall, the designer said no problem and no comment.
For those of you who have designed cantilevers before. Please just comment on your experience or research you have heard about supporting the beam with stiff walls such that no positive moment can develope in the midspan.
RE: supporting cantilever ends
It seems that you're asking whether this concrete column could be replaced by a steel column or concrete wall to support 'whatever is above the cantilever'. (When you say 'beam', engineers will generally think you're talking about a horizontal member in bending.)
The answer is, of course, "maybe". If you are relying on a column or wall, introduced under this cantilever beam, to carry gravity load, then it must have an adequate foundation and be considered in relation to entire structural system.
A column or beam under the 'cantilever' may work with the system that is in place, but like others have suggested, it could have ramifications that aren't apparent without considering the system as a whole. The stiffness of a new wall will affect the distribution of lateral load. A lone column may resist an uplift force when the backspan of the cantilever beam is loaded, changing the moment envelope of the beam.
A cantilever isn't necessarily a bad thing, but if you have discovered an overstress in the design, this might be a spot to add capacity to the structure.
RE: supporting cantilever ends
However, if this support is necessary, you could provide either RC as seen in the photo or Structural Steel. If you use structural steel or I-beam, erect this steel supported on a concrete pedestal at the base and provide steel plates bolted on the bottom of RC cantilever beam. There is a possibility that this I-beam shall be separated into two pieces and be welded at the middle height of column.
RE: supporting cantilever ends
I would fill the volume under that cantilevered slab with compacted granular fill, and call it a slab on grade, and be done with it.