A three-story wood-frame building will include a column with a design load of 21 k and is to be supported on a square footing. The soils at this site are silty sands, and the footing will have a depth of embedment of 24 inches. Compute the required footing width using the IBC presumptive bearing

Question

A three-story wood-frame building will include a column with a design load of 21 k and is to be supported on a square footing. The soils at this site are silty sands, and the footing will have a depth of embedment of 24 inches. Compute the required footing width using the IBC presumptive bearing pressures.

Accepted Answer

According to Table 17.3,

Soil or Rock Classification	Allowable Bearing Pressure,[latex]q_{A}[/latex]
Soil or Rock Classification	(kPa)	[latex](lb/ft^{2})[/latex]
Crystalline bedrock	600	12,000
Sedimentary or foliated rock	300	6,000
Sandy gravel or gravel (GW and GP)	250	5,000
Sand, silty sand, clayey sand, silty gravel, or clayey gravel (SW, SP, SM, SC, GM and GC)	150	3,000
Clay, sandy clay, silty clay, or clayey silt (CL, ML, MH, and CH)	100	2,000
Mud, organic silt, organic clay, peat, or unprepared fill	0	0

[latex]q_{A}= 3,000 lb/ft^{2} [/latex]

[latex]A=B^{2}=\frac{P}{q_{A} - \gamma _{c}D + u} =\frac{21,000 lb}{3000 lb/ft^{2}+\left(150 lb/ft^{3}\right) \left(2 ft\right) - 0} [/latex]

Solving gives B = 2.79 ft. This is greater than the minimum required width of 12 in (but need to check local building codes for possible additional requirements). Rounding to a multiple of 3 in gives B = 2 ft 9 in

Question 17.10: A three-story wood-frame building will include a column with...

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