Upside down Drop cap

[slickdeals]

Folks,
I am having a situation where there are planter boxes (2m x 2m) right above columns. The slab is supporting landscaped area.

Can I thicken the slab into the planter box to get more punching shear capacity? In essence, it would be a upside down drop cap.

I have never seen one like it and not sure if it even works.

Your thoughts are appreciated.

 

[msquared48]

I think that csd made a good point about possible future movement of the planter boxes. I, too, have seen this happen.

Although it would work, you might want to rethink this.

Mike McCann
MMC Engineering

 

[slickdeals]

All:
The planter boxes are irrelevant in this discussion. The deck is a landscape area. Any thickening I have above the slab will be hidden by dirt. For all intents and purposes, I don't care whether the planter boxes exist or not.

My idea started out as a thickening into the planter box. But I realized that it did not matter because of the thickening being hidden by soil above. In the sketch I sent, assume the planter boxes do not exist.

 

[hokie66]

Just as important as your structural design is the waterproofing of the landscaped area. Maybe that is not your responsibility, but you should gain some confidence that the waterproofing and protection thereof is first rate.

 

[csd72]

slickdeals,

My comment still stands. I have seen these landscape areas turned into cafes or similar at a later date. I have also seen engineers be too smart for their own good and create problems for future renovations.

These are soft requirements for sure but if you are just doing this to save the client a little money then you probably wont save them anything in the long run.

You are also introducing 4 additional corners to the waterproofing which is the greatest source of problems in these.

 

[hokie66]

Maybe I understood slickdeal's building differently from you, csd72. I thought the whole area was covered with maybe 600 mm of soil, and there are tree boxes over the columns, which would be a good place for the trees. Maybe I had a preconceived notion because I have seen it done that way. There has to be an allowance for kiosks, etc. on top, but that is typically included as live load.

Agree about the waterproofing. The edges of the upstand should be tapered so there are no sharp corners. And the waterproofing has to be protected from damage during installation of the landscaping materials.

 

[slickdeals]

@Hokie:
You are right about your assumption. Most of this deck is filled with 600mm soil with tree boxes over columns.

@csd72:
Good points on the waterproofing. Will certainly keep that in mind. Hokies suggestion of tapered perimeter will help.

 

[slickdeals]

All:
For your critique.

 

[Once20036]

A little bit off topic - but you don't reinforce the planter walls?

Most landscape folks around here aren't up on their concrete design & the Architect/Owner insists "It's concrete therefore it's yours to design" for site walls & sidewalks. It seems strange (to me) not designing concrete walls supported by an elevated concrete slab.

 

[hokie66]

slickdeals,
Looks good to me.

St20036,
I think most of us would show this type wall in a typical detail instead of in a major structural section. He has just referenced the walls here.

 

[rapt]

slickdals

The top bars in the drop cap need to "lap" with the top slab bars. They do not appear to have sufficient overlap to do this in your shetch. I would have them following the sloping concrete profile rather than a 90 degree crank to give a much longer "lap" and extending far enough into the slab to provide a full lap.

I hope when this was analysed for the PT effects and strength
- the drops were on the top as shown and not just on the bottom.
- the local effects around the drop for effective depth etc were separated from the calculations for the areas outside the drops.