I am planning to build a staircase in the vacation house with a rectangular steel profile as the base and then have the treads in wood. What I'm considering is how low a steel profile I can get away with without the staircase becoming wobbly.
I want to have as much free height under the staircase as possible, otherwise you risk hitting your head on the steel profile when passing underneath it. Therefore, I have looked at profiles with dimensions 150x100x5mm (which seems to be the thickest that can be easily found) and mount it horizontally. Could it also work with, for example, 120x80x5mm or 120x60x6mm, do you think? What is reasonable?
The staircase is quite steep, about a 45-degree angle, with 85 cm wide treads. The length of the stairway opening is about 270 cm and the total length of the steel profile will be about 360 cm.
I want to have as much free height under the staircase as possible, otherwise you risk hitting your head on the steel profile when passing underneath it. Therefore, I have looked at profiles with dimensions 150x100x5mm (which seems to be the thickest that can be easily found) and mount it horizontally. Could it also work with, for example, 120x80x5mm or 120x60x6mm, do you think? What is reasonable?
The staircase is quite steep, about a 45-degree angle, with 85 cm wide treads. The length of the stairway opening is about 270 cm and the total length of the steel profile will be about 360 cm.
My feeling is that what risks feeling most unstable is if you stand farthest out to the side on one of the middle steps and swing. The question is just how to calculate such a scenario?
I have my old "Tables in Technology" with various tables and formulas for different beams and load cases, but I can't quite figure out how to calculate this scenario. It was way too many years ago that I dealt with such things.
If anyone has any tips on how to make a rough estimate to determine a reasonable beam dimension, I would be very grateful!
I have my old "Tables in Technology" with various tables and formulas for different beams and load cases, but I can't quite figure out how to calculate this scenario. It was way too many years ago that I dealt with such things.
If anyone has any tips on how to make a rough estimate to determine a reasonable beam dimension, I would be very grateful!
Know-It-All
· Västra Götaland
· 12 323 posts
Are you planning to have the beam and cut out notches or weld on notches for the steps?
The first beam is of course the best, but I think the important thing is to achieve a really good attachment of the beam and stable steps.
The first beam is of course the best, but I think the important thing is to achieve a really good attachment of the beam and stable steps.
The question involves many interesting design and manufacturing challenges. The biggest problem, in my opinion, is how to handle the curved part of the steel profile. Should you weld parts of the same profile together? Personally, I would probably make the beam out of wood with a custom laminated construction where I steam-bend the different elements before gluing. Alternatively, the beam section could consist of two sections at a right angle resting on a pillar at the bend. The treads can take the curve in the way you've drawn.
From a structural point of view, there are two separate questions: the sizing of the beam and the attachment and sizing of the treads. The treads probably don't need to be calculated. Regardless of the type of wood, I think it involves steps about 45 mm thick. The main load will likely be in the middle. For the central beam, the critical load case should be a full-grown person standing in the middle of the staircase, assuming that the deflection should not exceed 1/300 of the length of the staircase. For simplicity's sake, I think you can assume a straight staircase. The maximum deflection would then be 1.2 cm. Since the staircase should have a 45° inclination, divide all loads by the square root of two to determine the load acting perpendicularly to the beam. The own weight is at most 50 kg/m. According to my quick calculation, you might manage with 70x70 with 5 mm wall thickness. In other words, this is more of a design issue than a structural issue.
From a structural point of view, there are two separate questions: the sizing of the beam and the attachment and sizing of the treads. The treads probably don't need to be calculated. Regardless of the type of wood, I think it involves steps about 45 mm thick. The main load will likely be in the middle. For the central beam, the critical load case should be a full-grown person standing in the middle of the staircase, assuming that the deflection should not exceed 1/300 of the length of the staircase. For simplicity's sake, I think you can assume a straight staircase. The maximum deflection would then be 1.2 cm. Since the staircase should have a 45° inclination, divide all loads by the square root of two to determine the load acting perpendicularly to the beam. The own weight is at most 50 kg/m. According to my quick calculation, you might manage with 70x70 with 5 mm wall thickness. In other words, this is more of a design issue than a structural issue.
As others have written, it's largely a matter of design and also of appearing stable aesthetically. I would never in my life make it in vkr 70x70 even if it might work. What do you think a potential buyer in the future would think when they see that..?
Regarding your problem, it is likely, as you say, that it might not be very torsionally rigid. It risks pulling unpleasantly at the welds depending on how you plan to manufacture. But place a column into the ground at step 5, for example, and you'll immediately have a much stronger staircase.
Regarding your problem, it is likely, as you say, that it might not be very torsionally rigid. It risks pulling unpleasantly at the welds depending on how you plan to manufacture. But place a column into the ground at step 5, for example, and you'll immediately have a much stronger staircase.
I'm not planning to make any notches in the beam for the steps; instead, there will be welded or possibly screwed brackets as the attachment for the steps. These could be made quite wide, maybe 50 cm, so that the steps have a broad and good attachment.
Just as you said, I'm also considering having support at the bottom end of the straight beam. It's likely that almost all the load is transferred to the floor there. Exactly how I will make the curved part I haven't figured out yet, but most likely it will consist of 1-3 joined straight parts instead of being completely rounded.
If you think 70x70x5mm is sufficient, I would probably choose a 120x80x5mm anyway. I have no problem with it being wider. It might just make it look more stable too. If one could know a bit more for sure that, for example, a 120x60x5 would also suffice, then that would be great, but better too robust than risking it being shaky.
What about the rotational force if you load a step as unevenly as possible? Is there any way to roughly calculate how much, for instance, a 70x70x5 twists in the worst-case scenario? Or is it perhaps nothing to worry about?
Thank you very much for the help so far. Now I can move on to thinking about how to solve the bottom part.
Just as you said, I'm also considering having support at the bottom end of the straight beam. It's likely that almost all the load is transferred to the floor there. Exactly how I will make the curved part I haven't figured out yet, but most likely it will consist of 1-3 joined straight parts instead of being completely rounded.
If you think 70x70x5mm is sufficient, I would probably choose a 120x80x5mm anyway. I have no problem with it being wider. It might just make it look more stable too. If one could know a bit more for sure that, for example, a 120x60x5 would also suffice, then that would be great, but better too robust than risking it being shaky.
What about the rotational force if you load a step as unevenly as possible? Is there any way to roughly calculate how much, for instance, a 70x70x5 twists in the worst-case scenario? Or is it perhaps nothing to worry about?
Thank you very much for the help so far. Now I can move on to thinking about how to solve the bottom part.
Don't skimp on the stiffness of the beam. The staircase will definitely be wobbly with a 70x70 beam. Closed profiles are torsionally stiff, so that's advantageous; however, it's important to consider the attachment at the top and bottom regarding torsion. In EKS 10, it states what loads the staircase should be designed for, 200kg/m2 or a point load of 2kN, these loads are in addition to the staircase's own weight. The best and most visually appealing solution is to weld your own small box beam from four plates, as plates are easy to bend. I would probably also make the steps out of plate and then cover the steps with the intended surface material, that way you can have thin and nice steps 
Then you really need to be skilled at welding. If we agree that aesthetics are most important, I find it hard to see how a home-welded beam could meet even low standards in this regard. There are several reasons to avoid steel, primarily the weight of the construction. A large steel beam with welded step brackets and treads will weigh several hundred kilos, which can be quite difficult to maneuver into a tight space. However, I do agree that the beam should be over-dimensioned regardless of material. It always looks better. But it's good to know where the minimum limit is.
I have constructed several advanced steel staircases for some of Sweden's leading architects, unfortunately, I cannot say they have low demands when it comes to aesthetics The heavier the staircases, the better if you're concerned about sway. Thumbs up for a nice staircase by the way
The heavier the staircases, the better if you're concerned about sway. Thumbs up for a nice staircase by the way It was never my intention to belittle bossespecial's knowledge about staircase construction. The idea of making a box girder from welded sheet metal is very creative if you want to make a double-curved structure. However, it assumes that one can utilize a welding company with competence and the right equipment. And that one can provide a usable drawing, which requires some knowledge of geometry. Having access to a good 3-D program significantly facilitates this.
I have designed quite a few staircases myself, with an emphasis on design and function. epkjoja's staircase looks elegant but has certain shortcomings in terms of function, which I think he should consider. 1) Very young and very old people do not like stairs without risers. With risers that are screwed and glued to the treads, the construction becomes stiffer, and the treads can have smaller dimensions. 2) For a staircase to be perceived as pleasant to walk in, one should follow the so-called stair formula. It states that 2 x rise height + tread depth should be 60 - 63 cm measured in the walking line. There is no information on the current floor height, but in a holiday home, it is usually 250 cm. With 14 risers, the rise height becomes 17.9 cm. 13 treads over 270 cm becomes 20.8 cm per step. 2x17.9 + 20.8 becomes 56.6. Such a staircase is not pleasant to walk on. You need to experiment with the number of steps to find the best solution. 3) A railing is important for many, both young and old.
I have designed quite a few staircases myself, with an emphasis on design and function. epkjoja's staircase looks elegant but has certain shortcomings in terms of function, which I think he should consider. 1) Very young and very old people do not like stairs without risers. With risers that are screwed and glued to the treads, the construction becomes stiffer, and the treads can have smaller dimensions. 2) For a staircase to be perceived as pleasant to walk in, one should follow the so-called stair formula. It states that 2 x rise height + tread depth should be 60 - 63 cm measured in the walking line. There is no information on the current floor height, but in a holiday home, it is usually 250 cm. With 14 risers, the rise height becomes 17.9 cm. 13 treads over 270 cm becomes 20.8 cm per step. 2x17.9 + 20.8 becomes 56.6. Such a staircase is not pleasant to walk on. You need to experiment with the number of steps to find the best solution. 3) A railing is important for many, both young and old.
The distance from floor to floor is 264 cm, so I have concluded that it would be best with 13 steps. That results in a step height of 203 mm, step depth of 218 mm, and a stair formula of 624 mm. It's the only way to satisfy the stair formula with the given measurements.
I must have a railing, at least on one side. I want to avoid risers even though I can see the advantage of them for rigidity. The staircase will be in the middle of the house, and I want to make it as "transparent" as possible.
Very good points! I will take them into consideration.
I must have a railing, at least on one side. I want to avoid risers even though I can see the advantage of them for rigidity. The staircase will be in the middle of the house, and I want to make it as "transparent" as possible.
Very good points! I will take them into consideration.
The load-bearing capacity can easily be handled with 120 mm in height. More challenging is ensuring that the steps don't tip sideways, i.e., when someone stands on the outer edge. One possibility is to have a corresponding support on the inner wall or within the inner wall and a sturdy plank that can withstand some overhang.
Alternatively, you can build a trapeze under each step that supports the middle beam.
Alternatively, you can build a trapeze under each step that supports the middle beam.