# Specific TIPS



## NCcarguy (Oct 17, 2007)

Well, since it's almost EXAM time again, and I was JUST solving a problem and got caught on a tricky item that I thought would be quite sneaky of NCEES to throw at us during the exam, I figured I would start a topic about items that I get tripped up on all the time. If any of you can think of others, please feel free to share

When you are solving a *BROAD CRESTED WEIR* problem, and if you get a depth over the weir.....that's actually *2/3 H*, and not *H*.

I know that, but I swear I miss it if I get in a hurry.

Any others you can think of?


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## IlPadrino (Oct 18, 2007)

NCcarguy said:


> Well, since it's almost EXAM time again, and I was JUST solving a problem and got caught on a tricky item that I thought would be quite sneaky of NCEES to throw at us during the exam, I figured I would start a topic about items that I get tripped up on all the time. If any of you can think of others, please feel free to share
> When you are solving a *BROAD CRESTED WEIR* problem, and if you get a depth over the weir.....that's actually *2/3 H*, and not *H*.
> 
> I know that, but I swear I miss it if I get in a hurry.
> ...


I don't know why, but weirs have always made me think twice... at the end of the day I think I've got them down, but the next time I look at them I have to rethink everything. I'm not sure what you mean above... Do you agree with the stuff at PE Notes-Hydraulics-Weirs?


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## Capt Worley PE (Oct 18, 2007)

I forgot about applying the wide beam rule when calculating deflection. And yeah, that was one of the distractors.


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## bigray76 (Oct 18, 2007)

In my WR notebook I made sure I had listed Manning's Equation several different ways so I didn't have to 'reinvent the wheel' depending on what I was looking to solve for AND should the units be Metric instead of US Customary.

-Ray


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## NCcarguy (Oct 18, 2007)

2 more I thought of

If the problem asks for a radius of horizontal curve...make sure they don't wan't the *CHORD* definition, instead of the *ARC* definition.

and if you have a geotech problem, make sure if they mention in the problem "A *saturated* soil" that means S=1 for all problem solving....I miss that one a lot too.


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## Road Guy (Oct 18, 2007)

always go with "worst case" or "safer" option , especialy if reading from a table or chart.


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## NCcarguy (Oct 19, 2007)

If you calculate the flows going into a pipe and it requires a 18.25 inch pipe.......an 18 inch pipe WILL NOT work, remember to go up one size!


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## bigray76 (Oct 19, 2007)

NCcarguy said:


> If you calculate the flows going into a pipe and it requires a 18.25 inch pipe.......an 18 inch pipe WILL NOT work, remember to go up one size!


Not only do you want to go up a size, but you want to go up to the next commercially available size!

-Ray


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## Suns Den (Oct 20, 2007)

NCcarguy said:


> 2 more I thought of
> If the problem asks for a radius of horizontal curve...make sure they don't wan't the *CHORD* definition, instead of the *ARC* definition.
> 
> and if you have a geotech problem, make sure if they mention in the problem "A *saturated* soil" that means S=1 for all problem solving....I miss that one a lot too.


rule of thumb

*chord for railroads n arc for highways*


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## Suns Den (Oct 20, 2007)

Captain Worley said:


> wide beam rule when calculating deflection


whaz this?


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## RIP - VTEnviro (Oct 20, 2007)

bigray76 said:


> Not only do you want to go up a size, but you want to go up to the next commercially available size!
> -Ray


I agree with you in real life about this one - the contractor is gonna look at you real funny if you spec out a 19" pipe. But I'm not sure if they make this distinction on the PE.

I would just pick the next biggest size listed among the answers.


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## Capt Worley PE (Oct 22, 2007)

Suns Den said:


> whaz this?


If a beam is greater than 8 times as wide as it's thickness, you have to multiple the deflection that you normally get time (1-(Poisson's ratio)^2)

It's in the MERM, but it is buried.


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## NCcarguy (Oct 22, 2007)

Here's another one that WILL come in handy.

On Horizontal Curves.....

If you are given the PI sta, and enough information to calculate the "T" distance, then asked for the PT sta.

You subtract the "T" distance from the PI to get the PC, then add the LENGTH OF CURVE to the PC, NOT the "T" distance from the PI, to get the PT sta!!!!


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## maryannette (Oct 22, 2007)

^^Be careful about the radius that you need. It could be centerline, edge of ROW, center of lane, etc.


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## NCcarguy (Oct 23, 2007)

maryannette said:


> ^^Be careful about the radius that you need. It could be centerline, edge of ROW, center of lane, etc.



Good point, pay attention to the formula, and WHERE the curve should be located.

another item......total vertical stress is soil, and pore water pressure, but for vertical effective stress you subtract the pore water pressure.


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## bigray76 (Oct 23, 2007)

Watch your units... look at how the question is asked and how the answers are given (in order to convert correctly as needed).

-Ray


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## rudy (Oct 23, 2007)

Watch out for the friction factor. The Darcy friction factor is NOT the same as the Fanning friction factor. Know what type of friction factor is specified on the friction chart you are using. f (Darcy) = f (Moody) = f (Blasius) = 4 x f (Fanning). NOTE: f (Fanning) is 4 times bigger.


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