Here is the situation. A mobility ramp is to be installed from a deck with a height of 0.6m. The recommended ratio is quoted as 1:12. Using that ratio, what is the included angle? Thanks.
botim,
Aug 4, 7:53pm
Maximum slope for hand-propelled wheelchair ramps should be 1" of rise to every 12" of length (4.8 degree angle; 8.3% grade). Maximum slope for power chairs should be 1.5" rise to 12" length (7.1 degree angle; 12.5% grade).
stevo2,
Aug 4, 8:26pm
You have a height of 600mm and have given a slope of 1:12 so your run will be 7.2mt. Your ramp slope will be 4.763641690726177 degrees
skifflebar,
Aug 5, 7:35am
Thank you for your replies, it is appreciated. Is it possible that you can explain the equation for me?
stevo2,
Aug 5, 8:29am
You have given a height of 600mm and a gradient of 1:12. Multiply the .6x12 and you get a run of 7.2mt. From there its easiest to take those measurements to an online trig calcutor like http://www.carbidedepot.com/formulas-trigright.asp and enter your dimensions. you will come up with the ramp angle I gave you in post #3 Cheers Stevo
tmenz,
Aug 5, 9:22am
Easy: 1 up for 12 along. Tangent of the included angle is height divided by length. arctan(1/12) = 4.76 deg or tan (4.76) = 1/12 = 0.0833
All real world measurements will be proportional to 1 and 12.
budgel,
Aug 5, 11:35am
I am interested as to why you need to know the angle. You already have the info needed to build it. No criticism implied, just curious.
skifflebar,
Aug 5, 1:07pm
That is the reason, curiosity about the process so I can apply the knowledge elsewhere if needed. Thanks to tmenz and stevo
h.e,
Aug 5, 1:50pm
There is a trig app for your phone now days, makes life easy as no need to work out if you need sin cos or tan. Just put in the 2 dimensions you have and what you want and done
skifflebar,
Aug 5, 2:27pm
Thanks h.e, I may look at that and I can see where quick resolution to a problem is necessary. But to be honest, I enjoy working my brain cells when I can ;-) I have played with the information that tmenz and stevo refereed me to and it is like giving your brain a pleasant 'back scratch'.
stevo2,
Aug 5, 3:06pm
You are welcome. Im a builder so I need to know how to work out angles for everything from ramps to rafters. The app makes it a lot quicker than using tangents as you can vary your measurements or angles very quickly and perform "What if" scenarios effortlessly.
skifflebar,
Aug 5, 9:55pm
An app is easier and quicker than a rafter square?
supernova2,
Aug 6, 12:52am
Probably, especially when you are up on the roof and the square is still in the ute.
stevo2,
Aug 6, 5:50am
Yes indeed. I have an icon on my phone has contains all of my work apps such as angle finder, stair calculator, Mitek guide, Gib Site Guide etc. Way quicker than old school methods. The only drawback is that people think Im texting in work time. The only time I use a rafter square these days is for the odd occasion when I need to use a larger than normal square.
tim41,
Aug 6, 7:08am
0.6 x12 =7.2,easy you don't need an app for that,blocklayer.com is a good site for heaps of building related calculations,stairs rafters fences rail setouts etc
bill1451,
Aug 6, 6:54pm
S oh C ah T oa old school Sine= opposite over hypotenuse, Cosine = adjacent over hypotenuse Tangent = opposite over adjacent, but then if you were born after 1970 you probably wouldnt know what log tables or a slide rule was let alone know how to use them.
h.e,
Aug 6, 8:31pm
I used log tables at school but then along came scientific calculators, they made life a bit easier but trig still sucked. It sucked even more when I had to relearn it for trade cert. Then bugger me days 20 odd years later my daughter asked one Friday night if I could help with her math homework, bloody trigonometry. Had to teach myself with the help of a bit of amber fluid and the internet. I started using it a bit this time, I found it could come in handy but it was barely worth the effort. Then a new employee at work put me on to the app, stuff soh cah toa give me an angle a length and I now can have the answer in 30 seconds. Apps rock and trig is easy
tegretol,
Aug 6, 11:32pm
You mean you don't carry one of those A5 grey-covered trig table books around in your back pocket these days?
stevo2,
Aug 7, 5:47am
Got rid of those at the same time we ditched the "Abacus" lol.
shanreagh,
Aug 7, 8:16am
That would be good . would have given much more room in the chariot.
PS Loved trig at school.
tmenz,
Aug 7, 8:24am
I've still got my 'Cambridge Log Tables' and my slide rule!
stevo2,
Aug 7, 5:39pm
I didn't like Trig at school and never paid much attention. I always thought "What a pointless subject, when am I ever going to use that in real life!" Now I'm using all the time in my work and coming on here giving others advice on how to use it.
shanreagh,
Aug 7, 9:57pm
Funny how that happens. I could never really come to grips with algebra though intuitively I knew it would be useful. was lucky at the last two jobs where I needed to do an algebraic equation there were workmates who had been able to figure it out and who did them for me.
golfaholic2,
Aug 8, 3:38pm
Still helps to know how to jiggle the equations about to get to where you want . True story , in the top math class at Shirleys Boys , the teacher was hopeless . All but one of us (son of head of maths dept and right swot) failed trig in the pre exam test . We gave up trying to memorise all the different permutations SOHCAHTOA could give you . so a heap of various equations with no real reason to use them in any given situation . the term SOHCAHTOA was never mentioned . With the small percentage of end of year result trig would give us , we naturally focused on what we could handle .
A week after the test , our teacher was away sick and a relieving student wrote that one word on the blackboard , SOHCAHTOA and BOOM .
Quite funny looking back
budgel,
Aug 11, 10:55am
Interesting. I never used trig . There is a method where a roof can be completely worked out in terms of Pythagoras theorem. Any part of the framing can be interpreted as part of a right angle triangle if you know the rise and run. Trig would have been handy for the angles, but we knew the pitch and used to make a bevel board with the required angles marked on them. You dont need a rafter to be much off straight for the angle cuts to not meet perfectly, so there was often a bit of adjustment required.
I'm all for using whatever method gets the job done. I would have used trig where applicable if I had it. The original question would probably have been answered by the draughtsman who did the drawings, but back in the day we used hands on methods for determining such angles. In the example above it would have been easy enough to mark out a 12: 1 angle on a sheet of something and take the angles with a bevel. Until the advent of the mitre saw, you didnt need to know the actual angle because you cut to the line the bevel marked.
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