Circular Stairway in Spherical Tank

edocket.access.gpo.gov/cfr_2007/julqtr/pdf/29cfr1910.24.pdf

Note the stipulation that each stair must, at a minimum, carry 1000 lbs moving, concentrated load. And the sphere shell needs to be designed for that as well.

.................. now I more than willing to help you out, and I enjoy helping others, however, I can foresee where/how this is going and I must reiterate - you should really have someone in person mentoring you.

Call up CBI, and see if they are willing to help you out (for a fee, nonetheless)

Hehe..

Thank you very much Mr. xmech..

I will examine your OSHA file. And i will also not forget your "reiteration" to find someone to train and supervise me!

Once more, thank you.

Oya, what is the formula to calculate the circular stairway? Maybe that one is for backup and comparison, because i have plan to use non-circular stairway, common stairway.

Hello Premium:

Some very basic and easy to follow instructions there, from the first respondent.

Can we have a little more detail,........

The tank size,

What is it made from,

What is it used for,

Is this a 'real' construction job or part of a project test?

If it is real work, is there more than one tank

Is there any connection flows or pipework at the bottom of the tank

Do you need stairs

Do you need a set of virtical safety steps 'fully covered' in case of a full? (Such as you may see on the side of a crane).

Do you need these to carry only one person or more

Will this person/s be carrying tools?

Have you considered a safety mechenism that will work on a stair rail,

If you need the spiral should it be enclosed and covered to preven falling

You should consider the height of the 'hand rail', to low and if there is no covering frame, it may be possible to fall over the side

As mentioned the Landing or two or more of them is a good thought from the first poster. But it may also be easier to move items up and down with landings which are not much more than six steps?

Can you explain to me how you are going to calculate the number of steps and the other points, where they apply please? This is very basic stuff. I would be seriously worried if you did not understand what you were going to do to work out the run of these steps.

Cost may come into it but, you may find a spiral staircase ready made for your perpose?.........Just a thought.

It matters, unless you have a seperate method of lowering tools the stair and steps have to be large enough to allow space for one or more people + tool boxes and or cleaning gear.

I wish you luck and would be most obliged if you can answer some if not all the questions above. They all should be in your mind as part of the design stage, OK?

Take care...........................

It is holiday, sorry i am late to check this forum..

My tank inside diameter is 21.216 meter. It is spherical.

It is made from SA 516 Grade 70

It is used for LPG storage

We are currently in the bidding phase with the deadline so tight (March 8).

It is four spherical tanks Sir.

Yes, there are any conections of piping.

Yes of course it needs stairs

"Vertical safety steps 'fully covered', sorry Sir i can not understand this part.

I need this stairway to carry around 2 persons with tool (tools for tank maintenance)

I have not consider the safety mechanism on stair rail. Could you please explain me about that.

"Spiral should be enclosed & covered to prevent failing", i can not understand this Sir. Then which one is better? To be enclosed or not? Because i dont know about this. Sorry.

There is any handrail to prevent failing. Middle handrail and top handrail along the stairway.

Well to calculate the numbers of steps is simply to divided length of stairway by its distance between step. I wish i am correct.

Readily waited for your comprehensive answer Sir. I am not in the US.

Thank you..

Hi Premium,

Please note that when a copy of a line or sentence is taken from your post, it is pasted in Italic and sometimes bold also. This is so you can see which line in part of the post is a description and which part is in reply to a particular question.

Thank you for your answers. Most seem OK! I hope you get at least a couple of days holiday! No need to to call me Sir, OK? Just bb will do fine!

I am not in the US either, I am mostly in the UK.

"Vertical safety steps 'fully covered', sorry Sir i can not understand this part.

I should have said Ladder not steps, sorry!

Go down to Page 11. Ref' 4.6.8 Stairways. Just below the stairway detail in mention of ladders with 'cages' to prevent falling.

I have not consider the safety mechanism on stair rail. Could you please explain me about that.

This safety mechanism can be a rope or cable running behind the person walking down. Or it can be a type of 'ratchet wheel' that can run the full length of the stairs, this has a connector for a safety-line. This is in case of an accident , exposure to gas, or illness etc, it allows easy recovery of the person/s who cannot walk back up the stairs themselves.

Spiral should be enclosed & covered to prevent failing.

This may not be necessary but I think it should be at least discussed in the design.

Well to calculate the numbers of steps is simply to divided length of stairway by its distance between step.

It depends on how you look at it as to whether you have given a correct answer. I would have said: you divide the height (20 M?) into steps, and each step onto any landings or temporary storage racks should be equal. If they are not it is easy to imagine someone slipping as they miss a step?

The steps should be galvanised steel grating type. And a minimum width of 750 mm and 275 mm deep (from heel to toe measurement). The first post said the minimum step should be 7"/175mm. I would imagine your measurement of 21.216 to be an estimate. The hatch you climb through at the top, does that encroach into the tank? Because you should measure to the top of the tank, to allow the correct number of steps but, also allow for the closure of the hatch, as it will need room to close. I have not checked the rules, but I would think one or two 'landings' part way down would be useful. Depends on how much weight a person is carrying really. The landings should be 750 mm deep and the width of the stairs of course. You can 'loose' any 'odd' mm at the top or bottom of the stairs. As oftentimes is is easier to work on 7"/175 mm steps and then have either a slightly deeper or shallower step as you climb onto the first, or off of the last. Are you making the steps? Or is it something you buy in from outside sources? It is a basic standard size and the fabrication may cost more than buying a staircase from another source?

Well you tell me roughly how many steps you will need? It does vary according to the exact measurements of the tank, so do not take my example I will give later as 'gospel'! It is for you to figure out.

You did very well but did not tell me how many steps the stairs should have.

Good luck and take care!...................

Oh ya sorry. I forgot to bold and italic the quotation Mr BB

Well actually there is only one vertical ladder, it is located inside the tank. But i have not designed it yet. Oh God there are lots of things to do

This safety mechanism can be a rope or cable running behind the person walking down.

Well i think there are no safety mechanism.

Anyways sorry, what standard do you use in designing stair Mr. BB?

Oh i see, it is better to take from another souce instead of fabrication by ourself.

And what about the thickness of the step? I use 6 mm for the thickness, i am afraid it will not comply to standard. The material is SA-36.

After these all completed, i will try to calculate the weight to determine the price.

Thank you to all of you here..

Hi Premium,

With the italics and or bold thing, I was just explaining. You do not have to do it but it makes reading the posts easier.

I am not saying it is better or what you should do is buy stairs from a supplier. But, it is one of the 'standard' items, and if time was short then it is worth giving it a thought?

Why are you angry? Have you calculated how many steps you will need yet, and did you have time to visit the link I sent?

Hi Premium,

This is what I meant by a caged ladder:

Take care..................

Hello jrpeck:

How are you?

There is not much happened in this thread at the moment, but as a basic strt you have given some good advice.

GA to you.

I doubt whether this chap, lady, is in the US. I would not much like anyone under me to have asked really basic questions like this.

Take care..................

Sir, my angle to horizontal is 40 degrees. And according to OSHA 1910.25, the rise (vertical distance between step) is 8" and tread (step) is 9.5".

Distance between step according to my calculation is 316 mm

This value was from: vertical distance between step / Sin 40.

I hope the calculation was correct and comply to standard.

Thank you all..

Hi Premium,

Tell me, just out of interest, what company do you work for, what is thier name?

Sir, my angle to horizontal is 40 degrees. And according to OSHA 1910.25, the rise (vertical distance between step) is 8" and tread (step) is 9.5".

Distance between step according to my calculation is 316 mm

This value was from: vertical distance between step / Sin 40.

I hope the calculation was correct and comply to standard.

-----------------------------------------------------------

I suggest you use either metric or non metric, do not mix them.

Can you explain how you reached the sum of 316 mm please?

vertical distance between step) is 8" and tread (step) is 9.5".

Is the 8" (~203 mm) the distance from the tread of one step to the thread of the next? The step depth 9.5" (heal to toe)?

Can you confirm this please?

Ups sorry that was unconsciously in mixing between inch and mm.

Yes, 8" is the distnce from one tread to the next tread in vertically.

Yes the depth (from heel to toe) is 9.5".

The value of 12.44" (316 mm) was came from : 8"/sin 40

Is it enough Sir? Thank you..

I am not sure why you want to go into so much detail just to calculate the cost of a stair for bidding. I would get a good budget number from a supplier of stairs and use it(maybe with a markup?) The good thing about this is that you can figure it exact later after you get the job. If time gets tight or you figure out that you can't build it as cheap then buy the stairs from the supplier and make your markup. One thing that is for sure the stairs supplier that knows his work can build it cheaper than someone who has never built stairs. I have built stairs several times before and they can be very hard to design so they come out right. There is nothing worse than to have to start over because the plans was not correct.