Homework Help: Compound bars question

1. Dec 15, 2013

anthonyk2013

A concrete column is reinforced with steel bars and carries a load of 20t. The overall cross section area of the column is 0.1m^2 and the steel bars accounts for 3% of this area.
Find the stress in the concrete
If the length is 4m< how much does it shorten.

E of steel 200GN/m^2
E of concrete 20 GN/m^2

Area of concrete =.1*97%/100=.097m^2
Area of steel=.1*3%/100=.003m^2
Area of concrete=.1*97%/100=.097m^2
steel=s
concrete=c

σs/Es=σc/Ec→σs=σc*Es/Ec→σs=σc*200/20→σs=10*σc

F=σs*As+σc*Ac
19.6*10^4=(10*σc*.003)+(σc*.097)
19.6*10^4=σc(10*.003+.097)
19.6*10^4=σc(.127)

19.6/.127=154.3*10^4
σc=154.3*10^4

My question is, the answer I have in my notes is 1.54MN/m^2. Why is my decimal point wrong?
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Dec 15, 2013

Fineline00

I'm not sure if it isn't. 1.54MN is the same as 1.54 x 10^6. 154.3 x 10^4 is the same as 1.54x10^6

3. Dec 15, 2013

anthonyk2013

Would be able to break that down more, still don't understand. Thanks

4. Dec 15, 2013

Fineline00

I just want to stress I'm not so sure on the physics but I feel it is just a error in standard form

Your notes give you the answer 1.54MN/m2, which is 1.54 Mega nm2 which is 1.54x106 N/m2 or 1,540,000 n/m2

5. Dec 15, 2013

anthonyk2013

Thanks

6. Dec 15, 2013

anthonyk2013

Appreciate if someone could check the physics work in my problem.

7. Dec 16, 2013

anthonyk2013

Anyone thanks