Pile Foundations in sign board tower of 80ft high
Pile Foundations in sign board tower of 80ft high
(OP)
There is 80 ft high sign board tower which is conisiting varying 1/2" thick & 2.5 (Average) Dia MS steel pipe with total weight of about 4.2 Tons.While the bearing capacity of soil is upto 0.9 tons/sft , one have designed 8 Nos 40 ft deep & 2 ft dia Reinforced concrete pile foundations for the said tower.Is there any alternative design to confirm the value engineering.However a wind pressure is minimal.
Regards
Mahesar
Regards
Mahesar





RE: Pile Foundations in sign board tower of 80ft high
RE: Pile Foundations in sign board tower of 80ft high
RE: Pile Foundations in sign board tower of 80ft high
Considering the piling drive machines transport, using more concrete and steel can make sense. Also, ascertain what a reasonably modulus of subgrade reaction will provide you with one good assessment of the rotation of the footing interface (use compression-only Winkler's springs). I would start using 4 (kgf/cm^2)/cm for a bad soil, that yours is. Further widening the footing will diminish rotation.
For poles giant lateral deformations nowhere else (in buildings seen) use to be allowed. So if the displacement at the tip under worst wind load is about H/150 a lots would applud, where in buildings rarely we would accept but H/400 or stiffer.
RE: Pile Foundations in sign board tower of 80ft high
RE: Pile Foundations in sign board tower of 80ft high
I agree with Ron --- you are going to have to deal with a rather large groundline reaction here. Even with basic wind velocities of 75 or 80 mph, after you get thru considering the gust factor, height factor and shape factor of the sign and pole shaft, you will have some formidable forces to consider coming into the foundation.
Also, Ishvaaag is correct in noting that you can allow huge lateral deflections and still not be detrimental to the pole (as long as you consider the P-Delta or secondary moments induced).
In my work in Florida (mostly sandy soil) with PCS towers and monopoles, as well as with high voltage transmission structures, I am faced with this problem every week. There are a couple of good programs available to help you in determining the proper burial depth to use. Vertical bearing is generally small enough to be handled with skin friction. It is the lateral resistance required (usually peaking at about 1/3 of the depth) that is hardest to cope with and generally determines the burial depth.
http://www.spiraleng.com
If you wish to visit my website, we can discuss these or other issues further.