Code Required Footing Ties

[StructuralEd]

Both the 2003 IBC (sect. 1805.4.2) and the ASCE 7-02 (sect.7.9.5.2) require "individual footing" ties in related to code sections on seismic loads for certain Seismic design Catagories.

Can anyone more specifically define "individual" footings?
In a rectangular building with perimeter column footings cast intregrally with the concrete frost walls, would those footings be subject to requiring cross ties perpendicular to the building? Or are the codes referring to isolated spread footings in the middle of the building space?

Also, since the footing excavations within the foundation area are backfilled with compacted structural fill, isn't that considered to afford a high degree of restraint for the foundation?

 

[StructuralEd]

ttt

 

[civilperson]

Individual spread footings shall be interconnected by ties. (ASCE 7-02, 9.7.5.2). This is not grade beams, pile caps, drilled piers or caissons, which are covered in 9.7.4.3. The compacted structural fill is confinement if the load specified is demonstrated to be restrained by the soil.

 

[strainman]

An individual footing would be one that is not attached to any other part of the structure laterally. Examples of individual footing would be a pile cap, or column footing that is too far below the slab to obtain lateral support from the slab. The idea here is to obtain lateral support for the footing through some other element of the structure. The compacted soil around the footing is not referred to in the section as offering any lateral support, therefore I would say the answer to your question is NO. Also, if the lateral loads are applied to the structure from seismic events, then the loads are actually applied to the footing through the soils you are using for restraint.

 

[StructuralEd]

So,
In a rectangular building with perimeter column footings cast intregrally with the concrete frost walls but occuring some distance below the slab, would those footings be subject to requiring cross ties perpendicular to the building?

 

[strainman]

According to my interpretation of the code, NO.