Mat foundation (22ft x 16 ft)
Mat foundation (22ft x 16 ft)
(OP)
I have to design a mat foundation (22ft x 16ft). Due to some environmental issues the maximum thickness of the foundation is limited to 30 in. Here are the details.
fc = 3ksi. I have used PCA mat to design the foundation. The thickness seems to be OK for flexure, punching shear and I am getting good results. The only problem where the punching shear is not satisfied is at one of the circular columns (Dia = 2ft). Here are the punching shear check details.
vu = 199 psi and vc = 164 psi.
vu - factored shear stress at the critical section
vc - factored shear resistance of concrete (without considering shear reinforcement)
Is there any solution for this problem. Can the bars provided for flexure reinforcement account for any shear resistance. Or can I provide any extra shear reinforcement to get this 30 inch mat work. Any suggestions regarding this will be greatly appreciated.
fc = 3ksi. I have used PCA mat to design the foundation. The thickness seems to be OK for flexure, punching shear and I am getting good results. The only problem where the punching shear is not satisfied is at one of the circular columns (Dia = 2ft). Here are the punching shear check details.
vu = 199 psi and vc = 164 psi.
vu - factored shear stress at the critical section
vc - factored shear resistance of concrete (without considering shear reinforcement)
Is there any solution for this problem. Can the bars provided for flexure reinforcement account for any shear resistance. Or can I provide any extra shear reinforcement to get this 30 inch mat work. Any suggestions regarding this will be greatly appreciated.





RE: Mat foundation (22ft x 16 ft)
DaveAtkins
RE: Mat foundation (22ft x 16 ft)
You can add shear reinforcement if you need using the ACI, but do not count the flexural reinforcement. It doesn't work that way. You can also build a base around the column to increase b0 to a suitable length, or use a stronger concrete f'c. Though you said you need 30 inches max, perhaps you can get away with increasing the thickness local to the problem columns only. I would go with something other than adding shear reinforcement.
RE: Mat foundation (22ft x 16 ft)
UcfSE,
I would probably go with increasing the thickness of the mat locally at the problem column. And I would like to know if there is any specific reason for not considering the shear reinforcement. Is it going to be expensive? Just curious
RE: Mat foundation (22ft x 16 ft)
RE: Mat foundation (22ft x 16 ft)
DaveAtkins
RE: Mat foundation (22ft x 16 ft)
You have the option of using the old load combinations and resistance factors if you follow ACI 318-02 Appendix C - "Alternative Load and Strength Reduction Factors."
RE: Mat foundation (22ft x 16 ft)