Florida Building Code-2001

[Murali27]

Hi all,

I am the new member joined today.

Design of foundation as per allowble stress method;

For the load combination of Dead + Live + Wind loads as mentioned in $1609.4.1 , Shall i increase the allowable bearing pressure of soil or allowable capacity of pile as per $1624.2 having not reducing the loading as per $1609.4.3

But in the clause $1624.1.4 "In no case shall the total load of the combined deand, live, wind and any other loads exceed the allowable bearing pressure of the soil or the capacity of any pile upon which the foundation is supported."

Please let me know either increasing the allowable stress or not.

 

[dlew]

Murali27,

There is the option of reducing the live and wind loads to 75% per 1609.4.3, OR increasing the allowable stresses (normally by 33%) as specified on the material section. To do both, reduce the loads and increase the allowable stresses, is NOT permitted. I do not think these paragraphs apply to foundations on high velocity hurricane zones.

My understanding about the foundation is as follows:
Paragraphs 1624.1.1 through 1624.1.3 are trying to keep the long term settlement of the foundations as equal as possible. Using that method, the soil bearing under the column with the largest percentage of live load to total load will be the allowable soil pressure when fully loaded. While the actual soil bearing under the other columns will be less than the allowable.

Paragraph 1624.1.4, in my opinion, is modified by paragraps 1624.2 and 1624.2.1. It is a remainder that the foundation has to be checked for dead plus live load, and also for dead plus live plus wind loads, since the allowable soil bearing is increased when wind is included.

To design the foundations I would use the dead load, plus the total reduced live load (per 1604.2) at the member immediately above the foundation for the preliminary sizing of the footings. Then I would check the footings for dead, live and wind loads, without reducing the live and wind loads to 75% as permitted on 1609.4.3.

If the wind load is less than 25% of the dead plus live loads, would neglect the wind load.
If the wind is more than 25%, would increase the allowable soil bearing pressure by 25% when using the total combined loads of dead, live and wind.
In other words, the allowable soil bearing pressure or the allowable pile capacity are increased by 25% for load combinations that include wind (instead of 33% as permitted for other materials.) Differently than clay, sand (this is Florida!) could consolidate quicker under transient loads.

Regards


AEF

 

[jcox]

I asked a somewhat similar question awhile back in regards to the IBC code(Thread 507-30353). The question was over what is a "transient load". The Florida Building Code seems to do a better job of defining this. Since the FBC is based on the IBC, I don't feel as unsure using the FBC's criteria for reduceing loads as I did for the IBC.

Just a point quick point on the FBC if you aren't familiar with it. Be careful in the hurricane zones and the different criteria that is required in design. I found out that the criteria was written by Miami-Dade and Broward county from the old SFBC. Many times there are contradictions in sections. I found out that this is due to each county's requirements.

Exampled:
2222.4 Structural Sheets. Unfilled decks and panels shall not be designed to at as diaphrams...

2223.8.5 Direct screw and attached roof and wall sheets may be used as diaphragms.....

Miami-Dade informed me that 2222.4 applied to them, and 2223.8.5 applied to Broward county. I have not contacted Broward county for verification.