Two immovable concrete blocks are connected wtih a 2.25 inch by 2.25 inch square
ID: 1368717 • Letter: T
Question
Two immovable concrete blocks are connected wtih a 2.25 inch by 2.25 inch square bar. At 68 degrees Farenheit there is no stress in the bar. If the bar heats from 68 degrees F to 94 degrees F, A) what is the stress in the bar? B) How much force do the blocks exert on the bar? The thermal expansion coefficient for aluminum is Usteel=6.5 x 10-C. Steel has a Modulus of Elasticity E=30x10^6psi.
We are working with the equations f=P/A or force=axial force/perpendicular resisting area
and also e=d/L or unit strain=total deformation (elongation)/original length of specimen in the load direction
Explanation / Answer
A)
Lets calculate change in length that occurs when heating
T1= 68 oF = 20 oC
T2= 94 oF = 34.4 oC
use:
deltaL / L = Usteel*(TF-Ti)
= 6.5*10^-6 * (34.4-20)
= 9.36*10^-5
stess = E* strain
= 30*10^6 * 9.36*10^-5
=2808 psi
B)
stress = F/A
2808 = F/ (2.25*2.25)
F=14215.5 lb
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