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Problem 17.5 A column transfers a factored load of 700 kips to a 9-ft square footing shown
in Figure P17.5, resulting in a factored uniform soil pressure of 8640 psf. Design the footing
reinforcement using strut-and-tie methods. Material strengths are f’c = 4000 psi and fy =
60,000 psi. Because footings typically contain no shear reinforcement, your design should
be based on unreinforced bottle shaped struts.
Strut and Tie data
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17.6 Redesign the footing in problem 17.5 using traditonal flexure and shear methods as
described in Chapter 15. Compare your solution to Problem 17.5 and comment on your results.
t
q
f’c4000psi fy60000psi
METHODOLOGY
1. Soil bearing is provided so no check of WSD is needed and step 1 is omitted.
2. Check punching shear. This check often sets the thickness of the footing.
3. Check slab shear.
4. Design flexural reinforcement.
5. Check bond and development length.
6. Check bearing stress under the column, especially if the column concrete strength is
greater than the footing concrete strength.
7. Check temperature and minimum steel requirements and sketch final design.
2. Check Punching (two-way) Shear
d h 4.0in32 in
4″ difference between h and d reflects 3″ cover and
1 to center of bars in two layers. H is less than the 36“
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Step 3 Check One-Way Shear along the face of the footing
wb
2dt
2
w 0.58 ft
Vuquwb Vu45 kip
lb
2
t
2
3.25 ft
qul2
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Step 6 Check Column Bearing Stress on Footing
If the column and footing do not have the same strength, an additional check is needed. It is
not required for this problem.