Construction PE
Well-known member
Sample Problem:
Due to a unique jobsite condition, a 20-in square column 12-ft high is to be concreted in 1-hr at a temperature of 60F (concrete). The maximum lateral pressure for the formwork is most nearly:
a- 1400psf
b- 1600psf
c- 1800psf
d- 1950psf
According to School of PE, the answer is:
Rate of placement is 12ft in 1-hr, so since R>7ft/hr use equation:
Pmax= (150) + (43,400/T) + (2800 R/T)
This gives an answer of 1433psf (so the correct answer choice should be A)
However, I have my doubts...
If you look at ACI 347, yes, the equation they used is for a rate of placement greater than 7ft/hr (ACI 347 eqtn 2.4) however, this equation 2.4 is for concrete placement in a WALL (problem states you are pouring a column).
ACI 347 provides a different equation to be used for concrete poured in a column... ACI eqtn 2.2:
Pmax= CwCc(150 + (9000R/T))
This "column" equation appears to be for all columns poured (not dependent on rate of placement)
If column eqnt 2.2 is used, the answer would be 1950psf (which would mean answer d is correct).
Lastly, if you look this topic up in CERM page 49-7 eqnt 49.3, CERM seems to agree with School of PE as they only present 1 set of equations (for placement <7ft/hr and for >7ft/hr). Neither CERM or School of PE make a distinction on whether a wall is being poured or a column.
I have come across a couple of similar problems and get them "wrong" for using the ACI 347 equation for columns.
Does anyone know if the PE exam would place more importance on rate of placement vs. what is being poured? Just wondering if I do need to use the "wall" equations to solve column problems during the test.
Any insight would be appreciated!
Thanks!
Due to a unique jobsite condition, a 20-in square column 12-ft high is to be concreted in 1-hr at a temperature of 60F (concrete). The maximum lateral pressure for the formwork is most nearly:
a- 1400psf
b- 1600psf
c- 1800psf
d- 1950psf
According to School of PE, the answer is:
Rate of placement is 12ft in 1-hr, so since R>7ft/hr use equation:
Pmax= (150) + (43,400/T) + (2800 R/T)
This gives an answer of 1433psf (so the correct answer choice should be A)
However, I have my doubts...
If you look at ACI 347, yes, the equation they used is for a rate of placement greater than 7ft/hr (ACI 347 eqtn 2.4) however, this equation 2.4 is for concrete placement in a WALL (problem states you are pouring a column).
ACI 347 provides a different equation to be used for concrete poured in a column... ACI eqtn 2.2:
Pmax= CwCc(150 + (9000R/T))
This "column" equation appears to be for all columns poured (not dependent on rate of placement)
If column eqnt 2.2 is used, the answer would be 1950psf (which would mean answer d is correct).
Lastly, if you look this topic up in CERM page 49-7 eqnt 49.3, CERM seems to agree with School of PE as they only present 1 set of equations (for placement <7ft/hr and for >7ft/hr). Neither CERM or School of PE make a distinction on whether a wall is being poured or a column.
I have come across a couple of similar problems and get them "wrong" for using the ACI 347 equation for columns.
Does anyone know if the PE exam would place more importance on rate of placement vs. what is being poured? Just wondering if I do need to use the "wall" equations to solve column problems during the test.
Any insight would be appreciated!
Thanks!