Footing Design Software
Design of Strap footing
Introduction
When two columns are reasonably close, a combined footing is designed for both columns as shown in below. When two columns are far apart, a strap is designed to transfer eccentric moment between two columns as shown in below. The goal is to have uniform bearing pressure and to minimize differential settlement between columns.
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Design assumptions
- Strap does not provide bearing.
- Strap is ridge enough to transfer moment from one footing to the other.
Design procedure
Service load design:
- Determine the length of exterior footing and its eccentricity, e.
- Determine eccentric moment, M = Pa*e.
- Determine shear force, V = M / L
- Determine footing reaction, Ra = Pa+V, and Rb = Pb-V
- Determine footing sizes for both A & B.
Structural analysis
- Calculate factored column loads, Pua & Pub
- Calculate factored eccentric moment Mu = Pua*e
- Calculate factored shear, Vu = Mu / L
- Determine factored reactions, Rua & Rub.
- Perform structural analysis, determine factored shear and moment on footings and strap.
Reinforced concrete design
- Design exterior footing. Check shear stresses and design flexural reinforcement.
- Design interior footing. Check shear stresses and design flexural reinforcements.
- Design footing strap as a reinforced concrete beam.
Service load design:
Design procedure:
- Determine the length of exterior footing and its eccentricity, e.
- Determine eccentric moment, M = Pa*e.
- Determine shear force, V = M / L
- Determine footing reaction, Ra = Pa+V, and Rb = Pb-V
- Determine footing sizes for both A & B.
Determine sizes of strap footing
Given:
Column information:
Column A: Live load = 40 kips, Dead load = 50 kips
Column B: Live load = 80 kips, Dead load = 100 kips.
Distance between two columns: 22 ft.
Footing information:
Allowable soil bearing capacity; 3000 psf
Distance from column A to edge of footing: 1 ft.
Allowable soil bearing capacity = 3000 psf
Weight of soil above footing = 120 psf
Depth of footing= 24”
Depth of soil above footing = 12”
Requirements: Determine the size of footing A & B.
Solution:
Assume a footing width of 6 ft, the eccentricity of footing A is e = 6/2-1=2’.
The distance between footing reaction, L = 22-2=20’
The eccentric moment is M = (40+50)*2=180 ft-kips
The shear produced by M is, V = 180/20=9 kips
Reaction at footing A = 40+50+9 =99 kips
Net soil bearing capacity = 3000-2*150-120=2580 psf
Required footing area of A = 99/2.58=38.4 ft2.
Use 6’ by 6.5’ footing, area = 39 ft2.
Reaction at footing B = 100+80-9=171 kips
Required footing area = 171/2.58=66.3 ft2.
Use 8’ by 8.5’ footing, A = 68 ft2.
Structural analysis of strap footing
Procedures
- Calculate factored column loads, Pua & Pub
- Calculate factored eccentric moment Mu = Pua*e
- Calculate factored shear, Vu = Mu / L
- Determine factored reactions, Rua & Rub.
- Determine factored footing reactions.
- Perform structural analysis; determine factored shear and moment
on footings and strap.
Determine moment and shear in a strap footing
Given: The strap footing in
Requirement: Determine maximum factored shears and moment in the footings and strap.
Solution:
Factored column load of A = 1.4*50+1.7*40=138 kips
Factored column load of B = 1.4*100+1.7*80=276 kips
Factored eccentric moment, Mu = 138*2=276 ft-kips
Factored shear, Vu = 276/20=13.8 kips
Factored footing reaction at A = 138+13.8=151.8 kips
Concrete Pier Design Software
Factored footing pressure per linear foot of A = 151.8/6=25.3 k/ft
Factored footing reaction at B = 276-13.8=262.2 kips
Factored footing pressure per linear foot at B = 262.2/8=32.8 k/ft.
Shear diagram:
At point 1: Vu = 25.3*1.5-138= -100.1 kips
At point 2: Vu = 25.3*6-138=13.8 kips
At point 3: Vu = 25.3*6-138=13.8 kips
At point 4: Vu = 13.8+32.8*3.5= 128.6 kips
At point 5: Vu = 32.8*-3.5=-114.8 kips
Moment diagram:
At point 1: Mu = 25.3*1.52/2-138*0.5= -40.5 ft-kips
At point 2: Mu = 25.3*62/2-138*5= -234.6 ft-kips
At point 3: Mu = 25.3*6*(6/2+13)-138*(5+13)=-55.2 ft-kips
At point 4: Mu = 25.3*6*(6/2+13+3.5)-138*(5+13+3.5)+32.8*3.52/2=194 ft-kips
Strip Footing Design Software
At point 5: Mu = 32.8*3.52/2=200.9 ft-kips
Spread Footing Design Software
Star trek armada 2000 download. Reinforced concrete design of strap footing
Design procedure:
- Design exterior footing. Check shear stresses and design flexural reinforcement.
- Design interior footing. Check shear stresses and design flexural reinforcements.
- Design footing strap as a reinforced concrete beam.