First time user - need help

[vento98sc]

I m working on a Pavement Analysis problem. I am using excel to find the equation relating the Stress to Resilient Modulus. Below is the table:

Stress Invariant (psi) Resilient Modulus (10^4)
12 10.34
30 20.27
60 31.58
120 52.63
12 10


I graphed it on a log-log and tried to find the best fit curve.
I went to chart then add trendline and display equation but none of the answers match the answer I m suppose to get. It is an exponential equation. So I have used the exponential option under trendline but I m still not able to get the answer.

Answer is to be: Mr = 1750 x θ^0.711

1750 is the Y-intercept and 0.711 the slope.

I m not able to get those results.

Anybody ? any idea ?
What am I doing wrong?

Thank you

 

[RalphA]

Assuming your equation to be Mr = 1750 x S^0.711, where S is the Stress Invariant in psi, and substituting various of the S values in your table, it seems that the answer needs to be multiplied by 10 to get Modulus of Resiliency (Mr) values that match your data airly closely. Could it be that the Y-intercept is actually 17,500, rather than 1750?

Now, my Excel 97 doesn't seem to be able to generate the semi-log charts that would be needed to look for the best fit, nor does it seem to allow a trendline, nor obtaining an equation, so, I can't help you further on this.

Of course, a "best fit" curve obtained by a program will rarely closely match one obtained by a human!

 

[vento98sc]

Thank you for the reply. I was able to figure it out.