Math wizards question

[RobertEVs]

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

 

[Jeff_M]

x= y/(g+s)

[Joe-Bouza]

0.5/0.075= 6.67'

[RobertEVs]

"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

[RobertEVs]

X= y/(g+s)

and

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

[fcernst]

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

[Jeff_M]

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

[Joe-Bouza]

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]

That the way I read it too

[RobertEVs]

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.

[fcernst]

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. 

[fcernst]

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. 

[Pointdump]

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

[Joe-Bouza]

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]

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

[RobertEVs]

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.

 

[RobertEVs]

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

[CahaLF7RX]

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

[Jeff_M]

This illustrates what @RobertEVs is saying. 

[fcernst]

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