HOW TO REDUCE COST IN CASE OF MINERATE FOUNDATION DESIGN

[nedians]

I have to design foundation for a minerate of a mosque having a height of 80ft., width 7ft. Slab are 4inches thick ( as given by architect). Bearing Capacity of soil is 1.5TSF @ 5ft to 8ft. Wind is the major concern and it is taken as 23psf lateral force on the minerate( Speed of wind is our city is taken as 100Mph).
I have very little idea how to perform this design as i haven't found any book on this topic. can any one please guide me some steps and guide ways to have a economical minerate foundation design. i want to know different ways which can help me in getting a economical design.

 

[austim]

Hi, Nedians,

I hope that I am correct in thinking that you are describing what I have always known as a minaret - that is the tower from which the muezzin calls the people to prayer ? If I am, then the basic foundation problem is just the same as for a chimney, lighthouse or any other tower. Try looking for references on chimney design.

Firstly remember that the footing needs to be large enough to avoid overloading of the soil below, and to provide a good factor of safety against overturning of the entire structure.

You need to calculate the total mass of the tower, plus the overturning moment due to wind. From then on, the traditional process is to assume some trial dimensions (Length*Width*Thickness) for the base, work out where the resultant total load acts (at the level of the underside of the footing), check foundation pressure and safety against overturning), and modify your base dimensions until you are satisfied with your design. If your tower is basically square (or round) in plan then length and width should be equal.

Remember when you are checking for overturning, that the support from the soil will not act at the edge of the base, but some distance inside (since you have to mobilize a sufficient area of soil to support the vertical loads).

Good luck.

 

[austim]

Hi, again, Nedians.

A second thought.

Whatever you do, DO NOT simply accept your architect's statement of the design wind pressure. 29 psf sounds a reasonable figure for 100 mph wind, but that is not the full story.

You must satisfy yourself on several questions:
* Is 100 mph a 'working' wind speed or an 'ultimate' speed?
* How does the shape of the tower affect the wind load ?
(ie although the 'basic' wind pressure may be 29 psf,
the total forces that it generates on a square tower
could be twice the load on a circular tower, because of
the different shape factors that must be used)
* What is the effect of the height of the tower?
Most wind records are standardised to a speed at 10
metres above ground level; depending on the height of the
buildings around the mosque, the wind speed at the top of
the tower could be 20% higher. That would increase the
wind pressure at the top by 44%, and give you a large
increase in overturning moment.