Stairs are harder to walk, and higher risk of injury than slopes (imagine falling from stairs versus falling from slope).
So why aren’t slopes used more commonly in buildings?
Even stairs-shaped escalators are more common than slope-shaped escalators.
**Edit:** By “slopes”, I mean “ramps”. Pardon my English.
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Slopes built with the same steepness as an average staircase will be too steep to climb. For a slope to be climbable it has to be shallow, which means it’ll be very long which 1) isn’t always possible to engineer, and 2) may take longer to walk
A ladder takes the most strength over the least distance. A ramp takes the least strength over the longest distance. Stairs are the midpoint between a ramp and a ladder.
As the others have pointed out, slopes require friction. You can STAND on horizontal ice, but you’ll immediately slide on a sloped ice-covered surface. You can climb icy stairs much more easily than you could an icy slope.
So forget about the ice (or that surfaces may be wet or covered with some sand), but still people may have shoes of varying “grip”, slipperiness, and practicality. It’s quite difficult to go up a slope wearing high heels. Or ski boots. Or sandals. Quite easy to use stairs with all of these types of footwear.
Try to find one of those [stairs that have a bicycle ramp](https://i.pinimg.com/originals/c5/a5/f5/c5a5f5e809b8d18060df82cd8ebd9f94.jpg) so you can directly compare stairs vs. ramp of the same climbing angle.
Slopes are much harder to climb.
Stairs have a horizontal surface, so you don’t slip. On slopes, there would always be a possibility of slipping because you rely on friction to keep you up. It would get really dangerous wjem wet or icy. Also, due to stair surface being horizontal, your foot / ankle is always at a natural 90° angle as opposed to slopes.
The slope is a method you can use with a lot of space. Stairs work pretty well between 30 and 40 degrees. Slopes max out at closer to 15- and that’s mighty steep.
In lots of places, when the sidewalk gets too steep the cut stairs into it
Your logic is completely wrong. A slope at the same angle as stairs is significantly harder to climb than the stairs
In winter, an icy set of stairs can still be navigable with time and careful footing. An icy slope of even a quarter grade that of stairs would be impossible for most adults and any heavy person to surmount without slipping back down.
Stairs built properly are actually safer and easier to use than a slope.
Slopes are great under good conditions – when the slope is of a gentle gradient and the conditions are good they can essentially be treated as flat ground and just walked on normally.
The problem occurs when you don’t have perfect conditions. When the slope gets steeper for example, it starts to require better balance to use (as you are no longer standing flat against the ground, but at an angle), and much more importance is put on friction between your feet and the ground – if that surface gets wet or icy for example, you now need to be able to prevent yourself sliding back down the slope, unlike a flat stair where you will remain stationary without any input.
When it comes to the decision to place one step at a change in height, or a ramp, generally it covers down to practicality and ease of use. A stair provides an instant change in height, and marked properly is obvious to users and easy to navigate. A ramp requires a much longer distance to ensure a gentle enough gradient, and the change from flat to sloped and back to flat again is more likely to unsettle someone.
The benefit of slopes is for things like wheeled trolleys which have trouble navigating steps, but again you need to ensure that the slip is long and gentle enough so as not to unsettle the contents of a trolley, or that too much effort will be needed to push it up a long, steep slope.
To this end, most countries provide legislation regarding slopes and stairs to ensure new infrastructure is suitable and safe for users – slopes should be kept to certain gradients, stairs should be of standardised heights and pitches, and both should be provided with suitable flat areas to allow users an opportunity to stop and rest of needed, and handrails for support.
TL;DR
Stairs are more space efficient than slopes, however we can only make slopes so steep due to accessibility. Generally speaking a step on a stair is 15cm high and 30cm deep (1:2 gradient) and a slope can at most be 0,5m high over 6m lengthwise, then you have to have somewhere to rest that’s 2m long and has a maximum slope of 2% (4 cm incline/decline over 2m). So arguably in buildings, it’s required space that’s the problem, therefore stairs and elevators instead of slopes.
Hopefully it cleared up some part of the question. I don’t know about escalators, but I would hazard a guess it’s about required space there as well.
I work as a civil engineer, designing roads, courtyards, football fields and other such things in Sweden so this might not fit a 100% of the time in all other countries but I believe most of the time it will. Generally if it’s outside and if it’s in the ground, I could be working on it making a drawing for the production side. So not inside of buildings, but the same generally goes when it comes to stairs and slopes.
You usually go for a slope when you have to make it accessible for people who might find it difficult to get up stairs for instance if you’re in a wheelchair. Now we can’t make the slope too steep because that would be an issue as well. There’s some rules and regulations that says that the most we can do slope to keep it accessible is 1:12, so 1 meter in height over 12m distance. However, the most we can do in one slope is 0,5m in 6m, but the gradient is still the same and after that we need a sort of flat surface for 2m, it can at most have a slope of 2%, so 4cm incline or decline on that “rest area” before you can do another slope or if you want to have a surface that’s 3%.
So what it sort of boils down to is that as long as we don’t have a slope that’s more than 2% we can go on forever essentially, but if it happens to be ‘steeper’ than that then every 0,5m of height we need to have a 2% slope for 2m as a form of rest area (best way I can describe it).
A step in contrast is usually 1:2 in its gradient. A normal step is about 15cm high (15-17cm) and 30cm deep (30-34cm) keeping the same gradient as 1:2. So it’s more space efficient to make stairs instead of slopes. Granted there are some stairs that we as humans might find strange or weird which are way deeper but only say 10-15cm high, we find these annoying to walk up usually because the stride length does not fully match with the effort and step depth.
Looking at cars and trucks (which of course doesn’t have stairs but you have to have some kind of gradient rules with those as well) we have a ruleset for those as well, depending on what type of road it is, in regards to how many vehicles will go down this road on average per day and what’s the purpose of this road, to get traffic in and out of a city center or a service road in the middle of nowhere?
So for roads you normally don’t want to go over 5% incline, but you can go up to 8% and in some cases you can go up to 12% but that will be very steep and in certain situations if there’s a pulley system for trucks, you could have it steeper perhaps up to 14%.
And as a final reference, we usually for roads have a slope on the side of the road that’s in grass and those are generally drawn with 1:3 (so 1m elevation over 3m length) but they can be done with 1:2 – 1:4 as well, these are the most common ones. There’s always some exception to the rule so to speak, but now you might have a general Idea of how it all sort of comes together.
You can fit a functional set of stairs in a smaller footprint than a ramp.
A 45° staircase is an easy climb.
A 45° ramp is damn near impossible.
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