1% Minimum in Concrete Columns? What is the theory?
1% Minimum in Concrete Columns? What is the theory?
(OP)
Hello fellow engineers,
Question 1 of 2:
Our ACI code specifies a minimum 1% steel in columns so that we don't have catastrophic failures such as in the Pakistan earthquake last year. I believe the minimum 1% is in there to provide 3 fold protection:
1) Ductility in the ends and joints, where rotation & hinges could occur.
2) 12% reserve axial strength if the concrete deteriorates at a joint.
3) Reserve moment capacity for unpredicted lateral forces.
Do you agree? Are there other reasons?
Question 2 of 2:
"Foundations" only require 0.5% steel, but if say a column continues down to a deeper foundation pad, is it correct to say that the column above grade is a "column" while the column below grade is a "foundation." Obvious, the soil does provide some confinement, and if it suddenly lost it's strength due to liquification, you'd probably have much bigger problems. And besides, you're not supposed to have hinging in your foundations anyway.
What do you think?
Question 1 of 2:
Our ACI code specifies a minimum 1% steel in columns so that we don't have catastrophic failures such as in the Pakistan earthquake last year. I believe the minimum 1% is in there to provide 3 fold protection:
1) Ductility in the ends and joints, where rotation & hinges could occur.
2) 12% reserve axial strength if the concrete deteriorates at a joint.
3) Reserve moment capacity for unpredicted lateral forces.
Do you agree? Are there other reasons?
Question 2 of 2:
"Foundations" only require 0.5% steel, but if say a column continues down to a deeper foundation pad, is it correct to say that the column above grade is a "column" while the column below grade is a "foundation." Obvious, the soil does provide some confinement, and if it suddenly lost it's strength due to liquification, you'd probably have much bigger problems. And besides, you're not supposed to have hinging in your foundations anyway.
What do you think?






RE: 1% Minimum in Concrete Columns? What is the theory?
2. The interface between the column and the foundation only requires 0.5% steel. If the column continues below grade, it still needs 1%.
RE: 1% Minimum in Concrete Columns? What is the theory?
It is advisable to continue the column steel all the way to the footing.
RE: 1% Minimum in Concrete Columns? What is the theory?
RE: 1% Minimum in Concrete Columns? What is the theory?
RE: 1% Minimum in Concrete Columns? What is the theory?
Say you need a 14"x14" column with 4#7 to carry an axial force, but the architect requires a 24"x24" column. Your minimum steel is based on 1% of the 14x14, and .5% of the 24x24, or 2.88in2.
RE: 1% Minimum in Concrete Columns? What is the theory?