Concrete Beam Test Beam Calculation

[durtaholic]

Hello All,

Was hoping for an explanation for a test beam calculation ... Have been beating my head against this for the last few hours and not coming up with the same number from a previous correct sheet .

The formula is R = 1.05 Pl / bd^2

P = Maximum applied load - 350
l= span length in " 18 "
b = width in" 5.88 "
d = depth " 6.04"

This formula should also achieve the same result but not making sense to me .
CF = Exact / Actual

R= 1.05( psi )CF / 145 .
Any help would be greatly appreciated ....
Thanks

 

[durtaholic]

After going back again and again I believe one formula will convert to modulus of rupture MPA and the other to modulus of rupture in PSI. I think my span link number might be off... Anyways , should have dug in a little deeper before I posted . The link is for CTM 523 which shows the actual formulas. If anyone can point me in a direction other than my forehead into a wall over and over would appreciate it ..Thanks

 

[Hoaokapohaku]

durt...I only skimmed through CTM 523, but it looks to me to be a Caltrans implementation of ASTM C78. The attached worksheet is one I created for recording data and reporting results for C78.

One difference there might be is that ASTM C78 provides two different formulae. Which one is used depends on where the break occurs in the beam. The attached worksheet applies the correct formula per the method based on the value designated "(a)" in the worksheet. When I glanced through CTM 523, it looked like the situation where the second formula would be used in C78, in CTM 523 it appeared that situation would be considered an invalid test. In actual experience, I've never seen a beam break in a location the second formula would be used.

All the cells shaded yellow require input either for calculation, or so that all the reporting required by ASTM C78 is in fact reported.

Feel free to use or adapt the worksheet as needed.

 

[Hoaokapohaku]

Curiosity got the better of me and I looked at CTM 523 again. What I said above about the differences between ASTM C78 and CTM 523 is wrong. The actual differences I notice are two.

1) CTM 523 seems to use a piece of equipment a little different, that requires converting the gauge reading to the actual lbf by reading a table. I suspect this may be where your problem is because the value you gave for "P" doesn't make sense. An MR of 650 would require a P value like 7800. Maybe someone provided you with the raw reading off the gauge rather than the converted value.

2) CTM 523 uses that 1.05 multiplier whereas C78 does not. My guess that is about the C78 precision statement, which states that the single operator coefficient of variation is 5.7%. By using the 1.05 multiplier, they nearly eliminate the possibility concrete may be rejected simply because of testing variation.

I'm sure there are other differences as well, but focusing on the calculation issues, I notice those two.

The formulas for PSI or MPa are the same. Whether the result is in psi or MPa is a function of the unit of the P value that is input, lbf or N.

 

[durtaholic]

Thanks for the insight Hoaokapohaku ... Had barely figured out the old method and then the state revised it .. Thanks again for the help ....