Grades on PnP Sheets divisible by 4...

[mbart87]

I was wondering why certain engineering conventions require profile grades on plan and profile sheets to be divisible by 4?

The explanation given to me was that they are easier to do field calculations on but I can't think of a time when you'd be dividing a grade by 4 in the field.

Thanks for any help.

 

[francesca]

We used to round slopes to one decimal because the contractors were laying out storm sewers with a laser rather than setting inverts.

 

[TerryScan]

Are you referring to the slopes being divisible by 4 or the vertical scale exageration for the profile drafting?

 

[mbart87]

Slopes being divisible by 4.

 

[brandonbw]

Do you have an example sheet to show what you mean? What kind of slope is divisible by 4? Where is that being required?

B+W Engineering and Design
Los Angeles Civil and Structural Engineering

http://bwengr.com

 

[beej67]

I don't understand the question either.

2:1 is as steep as we go around here, and that's with serious stabilization measures. 3:1 is standard for simple seeding. 4:1 is standard in Florida for sandier soils. Only one of these is divisible by four.

?



Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[TerryScan]

I think what some of us are saying is that we know of no "engineering conventions" that require the slope to be divisible by 4.

 

[e2010]

i dont think we are talking about sideslopes here. it is the longitudinal roadway profile being divisible by four evenly to 2 decimal places. i.e. a grade of 2.44 percent divided by four is 0.61. what is the purpose/benefit of this, or is it old tradition being carried on for no reason?

 

[CarlB]

Well based on the last reply I can invent a reason-
Survey stakes may need to be set every 25 feet, so the math is easier if there is an even difference every 25 feet, such 0.61' for the 2.44% slope.

 

[civilman72]

Carl - I think you are on the right track. My first job out of college was as a surveyor - we calc'd everything by hand, and having even numbers (stations, elevations, etc.) made it all easier. Shortly thereafter, during my first job as a design engineer, a lot of experienced engineers also pushed the use of even numbers - particularly to make things easier on the guys staking the job.

This was right around the on-set of ACAD becoming a common design tool. Over the last 15 years all designers and surveyors moved into CAD and I rarely see a surveyor calc anything by hand anymore. So, as a a designer, I see no point in rounding numbers like I used to 10-15 years ago.

 

[brendan35]

CarlB is correct. I was taught this methodology about 7 years ago, and I still use this method. Example, I use 0.52% rather than 0.50%.