landing at a deflection not greater than 45 degrees

[Allis Chalmers]

I do not see where the ICC117 requires a landing at a minor deflection (not greater than 45 degrees) in a ramp alignment, but can think that it might have something hidden in there.
Does anyone know of that? If it was curve formed alignment, then a landing is not specifically required. Obviously 90 degrees is covered.

Thank you.

 

[Yankee Chronicler]

I don't see where A117.1 DOESN'T require a landing at changes in direction less than 45 degrees.

 

[Allis Chalmers]

not sure that you understood my question.
Let me phrase this differently.
We aren't talking about a 90 or 180 degree turn, and not talking about a required landing for rise limitations.

If the ramp is a curve- and not more than 30 inches vertical (30 feet Horiz), then no landing is required.
If the ramp alignment is chorded instead of a curve, then how do you see that?

Meaning that the ramp run continues thru the deflection.

That is the question.

 

[Joe.B]

Being in CA I went first to 11B and I see this:

11B-405.7.4 Change in direction. Ramps that change
direction between runs at landings shall have a clear landing
60 inches (1525 mm) minimum by 72 inches (1829
mm) minimum in the direction of downward travel from
the upper ramp run.

"Change in direction" is not defined, so I thought I'd go see what the ADASAD says:

405.7.4 Change in Direction. Ramps that change direction between runs at landings shall have a
clear landing 60 inches (1525 mm) minimum by 60 inches (1525 mm) minimum.

Also not included as a defined term. But they do include this statement:

Advisory 405.7 Landings. Ramps that do not have level landings at changes in direction
can create a compound slope that will not meet the requirements of this document. Circular
or curved ramps continually change direction. Curvilinear ramps with small radii also can
create compound cross slopes and cannot, by their nature, meet the requirements for
accessible routes. A level landing is needed at the accessible door to permit maneuvering
and simultaneously door operation.

Would your scenario create any compound slopes?

 

[Allis Chalmers]

Thank you Joe

We are getting closer to the question topic now.
And not talking about door landings- those are clearly defined already.
The 180 and 90 degree corners are well defined already also.

I was not thinking about small radii.
So think of a larger radii curve. That would be a better approximation of a chorded alignment.
And now approximate that as incremental chords.

I think your advisory commentary has good food for thought.
Thank you

 

[Yankee Chronicler]

not sure that you understood my question.
Let me phrase this differently.
We aren't talking about a 90 or 180 degree turn, and not talking about a required landing for rise limitations.

If the ramp is a curve- and not more than 30 inches vertical (30 feet Horiz), then no landing is required.
If the ramp alignment is chorded instead of a curve, then how do you see that?

Meaning that the ramp run continues thru the deflection.

That is the question.

If it runs continuous, it pretty much has to be curved. That's not what your original post proposed.

The problem with curved ramps is that the slope in the direction of ramp travel cannot be steeper than 1:12 at any point on the ramp. Since with a curved ramp the inside of the curve is shorter than the outside, the inside edge is the steepest part of the ramp. The 1:12 slope has to be measured along the inside edge of the ramp.

I have no idea how you can do a chorded ramp (I assume by this you mean broken up into pie-shaped segments) without introducing uneven slopes.

 

[bill1952]

I do curved aisle ramps a lot. Elevation between landings and cross slope are what you have to comply with. Mine get complicated because it may start at 1:12, but usually much less at end.

 

[Joe.B]

I assume they're talking about something like this:

 

[Joe.B]

 

[Joe.B]

 

[Joe.B]

 

[Paul Sweet]

I think large radius curved ramps are OK as long as the inner edge is less than 1:12 and the cross slope isn't over 2%. I haven't seen anything definitive about how large a radius is necessary.

You are more likely to run into cross slope problems if you're trying to approximate a curved ramp with polygonal segments deflecting a few degrees instead of a smooth curve.

 

[bill1952]

I'm not sure how you measure cross slope on a circular ramp but presumably on the radius and that should be easy to have 0 cross slope.

 

[Yankee Chronicler]

I think large radius curved ramps are OK as long as the inner edge is less than 1:12 and the cross slope isn't over 2%. I haven't seen anything definitive about how large a radius is necessary.

You are correct. As long as the ramp slope in the direction of travel doesn't exceed 1:12 at the inside edge, the ramp meets standards. Many, many years ago, when reviewing such a ramp, I calculated what the minimum radius would have to be to maintain a 1:12 slope. I have long since forgotten that that minimum radius turned out to be.

But that works for a continuous slope. I'm not sure what the OP meant by "chorded," but if it means a bunch of segments then that suggests to me a series of slope changes -- and that, in turn, suggests that there should be a series of landings.

 

[e hilton]

I'm not sure how you measure cross slope on a circular ramp but presumably on the radius and that should be easy to have 0 cross slope.

It would have to be a radial line, because anything else will have a slope. Right?

 

[Yankee Chronicler]

It would have to be a radial line, because anything else will have a slope. Right?

That's my understanding. Cross-slope is measured perpendicular to the line of travel. If the line of travel is an arc, the radii are the perpendiculars.

 

[bill1952]

It would have to be a radial line, because anything else will have a slope. Right?

Yes but it's still planar, so shouldn't be a problem. You can get into the same question murky area with a very wide ramp. How do you be sure the path of travel is just down slope.

 

[Yankee Chronicler]

Yes but it's still planar, so shouldn't be a problem. You can get into the same question murky area with a very wide ramp. How do you be sure the path of travel is just down slope.

You can play that game with a wide stair, too, if you're into making games out of code compliance. A ramp goes up and down. The natural path of travel is the most direct route up or down.