A10 Foundations RA1010-140 Strip FootingsTable A1010-141 Section Through Typical Strip FootingGeneral: Strip (continuous) footings are a type of spread footing used toconvert the lineal type wall into an allowable area load onsupporting soil.Many of the general comments on isolated spread footings (Section A1010210) apply here as well.Strip footings may be used under walls of concrete, brick, block or stone.They are constructed of continuously placed concrete, 2000 psi orgreater. Normally they are not narrower than twice the wall thickness, norare they thinner than the wall thickness. Plain concrete footings shouldbe at least 8″ thick, and reinforced footings require at least 6″ of thicknessabove the bottom reinforcement. Where there is no basement, the bottomof footing is usually 3′ to 5′ below finished exterior grade, and 12″ below theaverage frost penetration (see Figure A1010-141), resting on undisturbedsoil. In some cases strip footings serve as leveling pads (stone walls, etc).Method of construction is affected by reinforcement and soil type. If steelmats and/or dowels are present and require accurate placement (frequentlyfor reinforced concrete or reinforced masonry walls), then side forms arerequired, as they are in wet or sandy soil. If there is no reinforcement oronly longitudinal reinforcement, and the soil will ‘‘stand’’ forms might beeliminated and economically should be.Preferably, strip footings are used on sand and gravel. The presence of asmall amount of clay or dense silty sand in gravel is acceptable, as is bearingon rock or chalk. They are sometimes used in uniform, firm or stiff clayswith little nearby ground vegetation, and placed at least 3-1/2′ into the clay.If the clay is sloped, there is potential for downhill creep. Footings up to

3-1/2′ wide are sometimes used in soft or silty clays, but settlement mustbe expected and provision made.Sloping terrain requires stepping the footing to maintain depth, since a slopedfooting will create horizontal thrust which may distress the structure. Stepsshould be at least 2′ long horizontally and each vertical step no greater thanthree-fourths the horizontal distance between steps. Vertical risers must beat least 6″ thick and of footing width. Potential for erosion of surroundingsoil must be considered.Strip footings should be used under walls constructed of unreinforcedconcrete, or of units bonded with mortar. They are also used when bearingcapacity of soil is inadequate to support wall thickness alone.Footings require horizontal reinforcement at right angles to the wall linewhen side projection of footings beyond the face of the wall is greater than1/2 to 2/3 footing thickness. Horizontal reinforcement parallel to the wallline should be used if soil bearing capacity is low, or soil compressibility isvariable, or the footing spans pipe trenches, etc. Vertical reinforcingdowels depend upon wall design.Alternate foundation types include bored piles, grade beams, and mat. Short,bored compacted concrete piles are sometimes competitive with stripfootings, especially in shrinkable clay soils where they may provide an addedfactor of safety. When soil bearing capacity is inadequate, grade beams canbe used to transfer wall loads across the inadequate ground to columnsupport foundations. Mat footings replace both strip and isolated spreadfootings. They may eliminate differential settlement problems.

Figure A1010-141Section Through Typical Strip Footing

“SLAB-ON-GRADE”

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ReferenceTables

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A10 Foundations RA1010-140 Strip FootingsExample: Strip Footing Cost Determination for Bearing Wall

Office Building . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 StoryStory Height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 VLFDimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50′ x 80′ = 4000 S.F.G.Exterior Wall. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12″ Brick and BlockInterior Wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8″ BlockFloor. . . . . . . . . . . . . . . . . . . . . . . . . . .Prestressed Concrete Slabs + 2″ ToppingRoof. . . . . . . . . . . . . . . . . . . . . . . . . . . .Prestressed Concrete Slabs, No ToppingSoil Bearing Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 KSFSuperimposed Load:

floor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 PSFroof. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40 PSF

A. Total load to each footing

Table A1010-143 Strip Footing, Load DeterminationWorking Loads

Type Load Reference Roof Floor Wall Total1. Total Load System B1010 229 90 PSF 175 PSF 95 PSF2. Load Span or Height Building Design 10 LF 10 LF 12 VLF3. Whole Bay Load/Level (Line 1 x Line 2) ÷ 1000 .9 KIPS 1.75 KIPS 1.1 KIPS4. Load to Footing/L.F. Roof + (Floor + Wall) .9 KLF 7.0 KLF 5.9 KLF 13.8 KLF

1. Total load from System B1010-229.2. Roof and floor load spans for exterior strip footings are 1/2 total span of 20′ or 10′ (wall height for our example is 12′).3. Multiply Line 1 by Line 2 in each column and divide by 1,000 Lb/Kip.4. Add 1 roof + 4 elevated floors + 5.33 stories of wall (includes .33 story for a frost wall) for the total load to the footing.

B. Enter System A1010-110 with a load of 13.8 KLF and interpolate between line items 2700 and 3100.

Interpolating: $42.60 + 13.8 - 11.1

14.8 - 11.1x ($49.00 − $42.60) = $47.20

C. If the building design incorporates other strip footing loads,repeat steps A and B for each type of footing load.

Table A1010-144 Cost Determination, Strip FootingsStrip Footing Total Length Cost From Cost x Length Total Cost

Description Type or Size Each Type (Ft.) System A1010 110 ($/L.F.) ($/Each Type) All TypesEnd Bearing Wall 1 100 $47.20 $ 4,720Non Bearing Wall 2 160 42.60 $ 6,816Interior Bearing Wall 3 150 98.00 $14,700 $26,236

Note: Type 2 wall: use “wall” loads only in Step A above.Type 3 wall: same as Step A above with load span increased to 20′.Interpolated values from System A1010 110 are rounded to $.05.

Figure A1010-142 Footing Plan

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