Sizing Concrete Foundation for Sculpture 2

[CDArch]

Hello all,

I'm helping a friend design an outdoor sculpture. My experience is mostly Aerospace so I'm a little out of my field. The final design will be checked and approved by the local city engineers, but I would like to get it right the first time.

The scultpure is basically shaped like an giant umbrella. (6ft high, 6ft dia, 400 lbs) After reading some posts on this forum I looked on ASCE to get the maximum expected wind in Seattle, and also found some books with good designs for the joints and supports.

What I would like help with is the foundation. The steel "handle" will be cast directly into a concrete block set in the ground. What sources can help me figure out how big the concrete block needs to be in order to hold the sculpture in place?

Thanks

 

[tincan]

If the statue is 6-ft in dia, I would start with a 6-ft diameter footing (no mowing or trash under).

For a paraboilc shape of 6 x 6, the projected wind area is 24 sq.ft.(A=4ab/3) Assuming a 15psf wind load the wind loading is 15x24=360#. The wind load is applied at the C.G. of a parabola which is 0.4(6)=2.4 ft from the bottom of the "umbrella". If the statue is elevated above the ground, add that height to the wind load lever arm. If its elevated 4 ft, the lever (moment) arm is 6.4 ft, and the wind load moment would be 6.4 x 360 = 2,304 ft-lbs.

The section modulus of a 6 ft dia circle is 21.2 ft^3. The wind load stress on the soil is M/S =109 psf. If you make the footing 2 ft thick, the weight of the statue and footing would be 269 psf.

Otherwise, a good basic mechanic of materials text book
P/A +- McI
Best, Tincan

 

[cap4000]

The best foundation books/sources I would go to, would be Braja Das and John Cernica. Essentially you have a footing, with an axial load and a bending moment, a subject with a lot of solved examples (P/A +/- Mc/I) by Soil/Civil Engineers. Good Luck

 

[CDArch]

Thank you. That's very helpful.

Das and Cernica have written several books, unfortunately none are in my local technical book store so I can't see which ones have the solved sets. I'll have to order one. Can you tell me which of these you were recommending?

Cernica
1) Fundamentals of Reinforced Concrete, Cernica, John
2) Geotechnical Engineering: Foundation Design, John N. Cernica, October 1994
3) Geotechnical Engineering: Soil Mechanics, John N. Cernica, January 1995
4) Geotechnical Engineering: Soil Mechanics and Foundation Design Set, John N. Cernica, April 1996


Das
1) Engineering Mechanics: Dynamics, Das, Braja M, January 1994
2) Engineering Mechanics: Statics, Das, Braja M
3) Fundamentals of Geotechnical Engineering, Braja M. Das, January 2000
4) Principles of Foundation Engineering (5TH 04 Edition), Das, Braja, January 2003
5) Principles of Geotechnical Engineering, Braja M. Das, September 2001

 

[cap4000]

John Cernicas book: Foundation Design in 1995. Chapter 6 is devoted to "Eccentrically Loaded Spread Footings". Good Luck.