ADA Switchback ramp

[richcrow1]

Here's on for you that will probably be more implemented as everything has to be ADA accessible.

Challenge:
I have to design a ADA switchback ramp with the following guidelines
Three rises in all (2) 28 ft ramps that are apart of the switchback and a 15 ft ramp leading from the switchback to the desired elevation needed. The ramp is needed to get from a 15 ft elevation to a 9 ft elevation in a confined space and meet ADA guidelines.

My problem, don't we all have them, I'm more of a water engineer then structural, but I work for a small firm and we make do.

My real problem is that I don't know what to design the base out of or structure itself. I started with a retaining wall but someone mentioned "concrete block". I don't quite know how detailed I have to be also in regards to the ramp. I hit google pretty hard but haven't had any luck yet.
I followed ADA guidelines to the tee as far as spacing, slope and handrails.

I'm a year out of school but that doesn't help much either. Just looking for a little advice or for someone to point me in the right direction. Standard or example would be good.

Thanks guys/ladies and I really appreciate your help.

~Rich~

I've attacched a few PDFs to help.

 

[graybeach]

richcrow1,
This problem is always tough. I have used mesa block to retain fill for supporting the bottom couple of ramp runs, where the ramp is close to the ground. After that, there are various ways to support the structure. When I was faced with a similar design problem, I drove around and visited some ramp structures to see what others have done. I'm in NYC so there are plenty of them around including a really cool one across from the Intrepid Museum in Manhattan. Hopefully you have some of them near you. Good Luck.

 

[cvg]

choice of materials will likely be determine partly if you are in or outside and what the surroundings are. For outside you could use reinforced CMU walls, reinforced concrete, a steel structure or even wood. I have also used gabions to support an ADA ramp near a flood channel.

 

[richcrow1]

Thanks guys and that's difinetly a start. "Mesa block" is a idea to hold the foundation in.

I think one of my challenges is that I live in South Florida, which is pretty much flat. Retaining walls, ADA switchback is not a common thing around here.

I'm getting along pretty good in the design. Although the CAD, details and specs are killing me, but here are a few more questions.

How do I or should I connect the retaining wall to the switchback ramp?

I can envision putting the typical retaining wall up with a standard typical gravity wall on both sides, and then laying the concrete block down to keep the foundation in. lastly, laying out the concrete form work to lay down the ramp.

Second question
How detail do I have to be regarding the ramp itself? Is that up to the conctractor? Form work? Which kind of handrailings to use? Handrail post installment (How far do they have to be apart)?

Wow this seems like they should have really hired a geostructural engineer to do this. But hey, I'm low man on the ladder. On the bright side, I'm learning so that's what counts.

Again, if you guys have any ideas it would be greatly appreciated.
Thank you,

~Rich~

Water is so much easier in South Florida.

"Water flows down hill"

 

[graybeach]

I think you answered your first question. At the end of your retained fill ramp, you could have a concrete seat that would support the beams that support the ramps.

The second question is sort of scattered. I would leave the formwork up to the contractor. But I would definitely fully design the railings myself. The ADA guidelines are very specific as to the railing configuration. Study them carefully and make sure your railing complies to the letter. The same goes for slopes, length of runs, sizes of landings, etc. If the ramp does not exactly meet the requirements, it is likely that you will be sued by advocates for the disabled. Drainage can also be tough, but at least you do not have to worry about ice.

Do you have someone familiar with the codes who can review the design? We have an in-house code expert who rakes everyone over coals. Painful but worth it. I just designed some ADA compliant picnic tables. Wow - you would never think something could be so complicated! Anyway - it would be a good idea for you to find such a person, maybe on a consultant bases.

 

[JKW05]

I tend to design the walls as cantilvered retaining walls (reinforced concrete or masonry), but prefer to bear the slab on top and tie it into the wall to prevent any long term movement in the wall. I generally don't use formwork, but pour the slabs on fill. Having said that, I also generally reinforce the slabs as structural slabs spanning between the walls, and count on fill as the formwork only.

ICC/ANSI A117.1 has requirements for ramps (referenced by IBC). Here are some points to check that come to mind (Assuming you are under IBC):

1) You will need an extended surface, or a curb or barrier, at the edge of ramp(s).
2) You need to extend the handrails 12 inches past the beginning and end of the ramp.
3) If grade difference to an adjacent surface is >30" you will need a GUARDrail AND a HANDrail.
4) There are opening limitations between ballusters for GUARDrails.

 

[richcrow1]

Wow, I wouldn't of thought but I sure did hope for some kind of help. That was really helpful and calcs/design for that idea are easier and make better sense. To be honest, that was my first idea. To just cut a triangle out of the side of the hill and lay the ramp down. But my PE didn't like it. Not her fault though, just not experienced in structures.

Just so I'm not mistaken. A retaining wall, both sides have a gravity wall and then a (let's say a 8 inch) slab connecting it all. Then the form of the ramp on top. That just sounds so much easier and makes structural sense.

One last question that just popped up. Where would you connect the slab to the (2)gravity walls and retaining wall. At the footing, on top of the footing or above it?

Again, thank you and for those who want to know I'll keep this thread updated to see if it works or gets approved.

 

[JKW05]

Not sure what you mean by "(2) gravity walls and retaining wall".

Perhaps my concept is better described by first assuming a single-run ramp:

1) Design each side wall as a cantilevered retaining wall to hold back the compacted fill inside.
2) Cut the block, or form the top of the wall to match the slope of the ramp and place and compact the fill to match the top of the wall.
3) Pour the slab on the fill and extend it over the top of the wall. I usually place reinforcing dowels bent 90 degrees to tie the slab into the wall (these have to be installed with the wall). Movement of the wall over time is countered by tying the slab into the wall.
5) By designing the slab to span between the walls, concerns about the slab settling over time is eliminated. (The fill only has to hold the concrete up until it hardens).

The common wall at the switchback may be confusing things here. In that case, I would add a shelf in a thicker wall to receive the slab at the lower ramp run. (i.e, the wall might be 12" thick below the lower ramp slab, and 8" thick above the lower ramp (creating a 4" shelf).

The slab would not be tied into the footing at all! The wall is doweled into the footing as part of the retaining wall design. I would place the footings at frost depth, but I guess in So. Fla. you wouldn't have that requirement. Check if your building code has requirements for minimum footing depths. Otherwise, just make sure it is deep enough to satisfy the retaining wall design.

Please note that the construction I described requires excavating to the propoer footing elevation(s) and backfilling between the walls; not just "cutting a triangle" into the hill and pouring concrete on it.

I hope this is a little clearer for you. Good luck!

 

[richcrow1]

JKW05,

I don't know what to say? I hope just a thank you will do. With one semester of concrete, that I don't even remember, I was stuck. You've helped me out here "Tremendously". All of you. I've been put in a bad place and expected to get out with out any guidance. Engineering? I don't know but I do know that I'm truly greatful.

~Rich~

P.S. So where should I tell the firm I work for to send the bill to?

 

[ACtrafficengr]

Rich,

Sounds like you should give JKW a star!

"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928

"I'm searching for the questions, so my answers will make sense." - Stephen Brust