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## Math wizards question

26 REPLIES 26
Message 1 of 27
1197 Views, 26 Replies

## Math wizards question

How would you determine "X" and "Y" when you have a 1% slope or anything except 0%? 0 would be easy to determine.

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26 REPLIES 26
Message 2 of 27

x= y/(g+s)

Jeff_M, also a frequent Swamper
Message 3 of 27

0.5/0.075= 6.67'

Joe Bouza
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Message 4 of 27

"0.5/0.075= 6.67'"

Me thinks you missed the 1% Flowline grade part.

It actually comes out to 1% running slope with curb height of 0.5'

Ramp UP 7.692'

(100*0.5)/((7.5-1.0)*100)*100

Ramp DOWN 5.882'

(100*0.5)/((7.5+1.0)*100)*100

Message 5 of 27

X= y/(g+s)

and

Message 6 of 27

The way I read your diagram is that you need to drop 0.5' at a rate of 7.5ft/100ft = 0.075 ft/ft to complete the small triangles...the flowline grade is irrelevant. The 0.5' perpendicular segment rotates continuously relative to the flowline at a constant 90 degrees.

0.5ft/7.5ft/100ft = 50ft^2/7.5ft = 6.7ft

Fred Ernst, PE
C3D 2025
Ernst Engineering
www.ernstengineering.com
Message 7 of 27

Well, using the formula I posted: 0.075 + (-0.01)  You just plug in the negative slope value.

Jeff_M, also a frequent Swamper
Message 8 of 27

I don't think so. the height of the curb ramp does not care about the slope of the road. Ped ramp wings rise 1 on 12 8% they don't care what the slope of the road is

Joe Bouza
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Message 9 of 27
That the way I read it too

Joe Bouza
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Message 10 of 27

0.5ft/7.5ft/100ft = 50ft^2/7.5ft = 6.7ft

I'm confused a bit here I'm trying to understand where you are coming from but If I take a featureline that is @-1% grade and set an elevation point then offset another to 6.7ft from that I do not wind up with a 7.5% grade but 8.47% instead. Also, that puts the top elevation at 0.4' and not 0.5'. Therefore, the flow grade is relevant, not to mention that the offsets at 7.5% are both different dimensions when using a grade for a flowline. In my case Ramp UP=7.692ft. and Ramp Down=5.882ft.

Message 11 of 27

Assuming those are two right triangles each with a height of 0.5’ .. the 0.5’ height segments maintain a constant relative 90 degree relationship with their base (i.e. flowline here) regardless of the absolute rotation angle of their bases.. making the i.e. flowline slope irrelevant in their base length calculations.

Fred Ernst, PE
C3D 2025
Ernst Engineering
www.ernstengineering.com
Message 12 of 27

Assuming those are two right triangles each with a height of 0.5’ .. the 0.5’ height segments maintain a constant relative 90 degree relationship with their base (i.e. flowline here) regardless of the absolute rotation angle of their bases.. making the i.e. flowline slope irrelevant in their base length calculations.

Fred Ernst, PE
C3D 2025
Ernst Engineering
www.ernstengineering.com
Message 13 of 27

Hi Robert,
Figure is misleading. It looks like "X" is measured along the 1% slope flowline, which would be 7.698078'. I think what you're really looking for is horizontal alignment length, which would be 7.692694.
Dave

Dave Stoll

64GB DDR4 2400MHz ECC SoDIMM / 1TB SSD
Windows 10 Pro 64 / Civil 3D 2024
Message 14 of 27

Typica ADA requires the maximum rate of the flare to be 8% 1:12 which is 6’ for a 6” rise. The ped ramp does care about the slope of the road.

Joe Bouza
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Message 15 of 27

This not what the original diagram shows. The throat is the same level as the flow line and rises independently of the flow line

Joe Bouza
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Message 16 of 27

Am I missing something here? Would not one ramp be longer on one side than the other when there is a gutter flowline true slope? When I lay these out, they tend to come out that way. In other words, 6.67' will not yield 7.5% ramp. If you come off a landing and head towards the upward side of the sloping sidewalk a ramp at 7.5% is going to take a bit longer to achieve than the downward side.

Message 17 of 27
What is a throat joe? If that is the landing 2% is max or 1.5% design in any direction
Message 18 of 27

Hello again.

Joe is correct.  the curb height is 0.5 ft and that is and both ramp ends.

it has to be or else your sidewalk is not matching the roadway slope.

(and that is a design nightmare)

best of luck,

nonbeard13

Message 19 of 27

This illustrates what @RobertEVs is saying.

Jeff_M, also a frequent Swamper
Message 20 of 27

Those aren’t 6” drops as shown in the original diagram though..

Fred Ernst, PE
C3D 2025
Ernst Engineering
www.ernstengineering.com

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