topic Re: Math wizards question in Civil 3D Forum

Math wizards question

RobertEVs — Wed, 24 Jul 2024 16:33:09 GMT

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

Re: Math wizards question

Jeff_M — Wed, 24 Jul 2024 17:27:38 GMT

x= y/(g+s)

Re: Math wizards question

Joe-Bouza — Wed, 24 Jul 2024 19:21:40 GMT

0.5/0.075= 6.67'

Re: Math wizards question

RobertEVs — Wed, 24 Jul 2024 20:03:47 GMT

"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

Re: Math wizards question

RobertEVs — Wed, 24 Jul 2024 20:18:32 GMT

X= y/(g+s)

and

Y= y/(g-s) for down grade

Re: Math wizards question

fcernst — Wed, 24 Jul 2024 20:38:49 GMT

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

Re: Math wizards question

Jeff_M — Wed, 24 Jul 2024 20:41:36 GMT

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

Re: Math wizards question

Joe-Bouza — Wed, 24 Jul 2024 20:47:26 GMT

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

Re: Math wizards question

Joe-Bouza — Wed, 24 Jul 2024 20:53:26 GMT

That the way I read it too

Re: Math wizards question

RobertEVs — Wed, 24 Jul 2024 21:06:56 GMT

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.

Re: Math wizards question

fcernst — Thu, 25 Jul 2024 01:47:22 GMT

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.

Re: Math wizards question

fcernst — Thu, 25 Jul 2024 03:02:08 GMT

Re: Math wizards question

Pointdump — Thu, 25 Jul 2024 09:35:32 GMT

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

Re: Math wizards question

Joe-Bouza — Thu, 25 Jul 2024 15:01:08 GMT

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.

Re: Math wizards question

Joe-Bouza — Thu, 25 Jul 2024 15:04:53 GMT

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

Re: Math wizards question

RobertEVs — Thu, 25 Jul 2024 15:46:50 GMT

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.

Re: Math wizards question

RobertEVs — Thu, 25 Jul 2024 15:48:50 GMT

What is a throat joe? If that is the landing 2% is max or 1.5% design in any direction

Re: Math wizards question

CahaLF7RX — Thu, 25 Jul 2024 19:21:21 GMT

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

Re: Math wizards question

Jeff_M — Thu, 25 Jul 2024 22:00:31 GMT

This illustrates what @RobertEVs is saying.

Re: Math wizards question

fcernst — Thu, 25 Jul 2024 22:36:41 GMT

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