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Raab arch3355 construction iii spring 2013 arm stem

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Unformatted text preview: tion III | Spring 2013 arm / stem toe cantilever wall Column Footings: General Considerations Simple spread footings act much like inverted beams Upward soil pressure is a continuous load that is resisted by the downward column action Causes bending in the upward direction; inducing compression near the top of the footing and tension in the bottom of the footing If tension is great enough, tension reinforcing must be added near the bottom of the footing. heel key Column Footings: General Considerations shallow bearing [foundations / spread footings] deep foundations [piles / piers] Lightly loaded walls with narrow footings: -  Bending not critical [no reinforcement] -  Width and thickness are designed to resist the wall load and shear forces using only the strength of the unreinforced concrete compression in top of footing ravity wall -  Longitudinal reinforcing isgincluded for temperature reinforcing and to help the footing span intermittent, weaker soil conditions column load [P] compression in top of footing d d column load [P] b distance “d” from the face of the wall [critical section for shear] a d/2 e g face of wall [critical section for moment] f h d upward soil pressure tension reinforcing 3” cover one-way shear line tension in bottom of footing upward soil pressure two-way or punching shear line c effective depth “d” is the h distance from top of the footing to the centroid of the reinforcing steel ld d counterfoot tension reinforcing face of column: [critical section for moment] h/3 development length of reinforcing steel tension in bottom of footing ARCH3355 | Construction III | Spring 2013 FOUNDATION DESIGN | P. RAAB ARCH3355 | Construction III | Spring 2013 12” 12” counterfoot 36” 5’ below grade d FOUNDATION DESIGN | P. RAAB P=Wxh 12” #8 bar [1in dia] d d d d d 3” cover ld ld ld 12” 1 12” #4 bars [7in o.c.] d d d d 4/25/13 Column Footings: Critical Sections Wall Footings: General Considerations -  One-way shear: soil design pressure is calculated over the rectangle [abcd] Determination of the Footing Width: Determined by allowable bearing pressure by assuming a footing thickness and designing for the total load – including the weight of the footing – then verifying the thickness is adequate for shear and bending. -  Two-way shear: soil design press...
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