Consider the following beam section. It has a concrete compressive strength of 4,000 psi and Grade-60 bars. There are 4 #9 bars at the top and 9 #10 bars at the bottom. The area of a single #9 bar is 1.0 in.² and the area of a single #10 bar is 1.27 in.². The section is subjected to a positive moment with the top bars in compression.
Answer
ACI code 318 states that the member whose computed tensile strain '' is equal to greater than the 0.005( 0.005)
at the same time the concrete strain is 0.003 are to be refered as tension controlled beam.
To calculate the tensile strain we have =
d = effective depth of beam
c = Neutral axis location from top
Calculation of 'd'
d = distance from extreme compression fibre to the centroid of steel bar
d = h - centroid of steel bar from bottom
h = 10+12+5
h = 27 in
To calculate centroid of steel bar from bottom we can use centroid formula
we have bottom 3-#10 bars centroid at 3 in from bottom, middle 3-#10 bars centroid at 5.5 in from bottom and top 3-#10 bars centroid at 8 in.
centroid of steel bar from bottom = (since all 9- #10 bars have same area it will cancel out)
centroid of steel bar from bottom = 5.5 in
Now d = 27- 5.5
d = 21.5 mm
Trending now
This is a popular solution!
Step by step
Solved in 3 steps
