Where can I find a book on frame/pipe scaffold design? 1

[anchorengineer]

I am being asked to design frame/pipe scaffolding. I am looking for capacity information on the web but can't seem to locate it. I can't even find a manufacturer located in the US. Is there a design book/manual that anyone knows about?
Thanks!

 

[anchorengineer]

OK. It's always the case when you finally ask the question you find (at least part of) the answer. I found (2) manufacturers in the US. Astro and STVA. I was able to find ultimate loads on the STVA website. Now all I need is a scaffolding design guide book just for a reference. Thanks!

 

[MiketheEngineer]

I can probably help you - since I do that all day long. There are about three main types of "system" scaffolding -
Cup-type, Safway and SureLock (or pin lock). These all use 1.9 steel tubing for the main structural members and go together kind of like K'nex toys. I have left out the frame types of scaffolding -- but that is a whole other type.

To get you started go to BEIS.com or Safway.com. You could also see OSHA CFR part 1926 - subpart L. The gospel on scaffolding safety.

Any questions - just post here.

 

[anchorengineer]

Thanks Mike. The Safeway Scaffold Technical Manual seems to be very comprehensive. Do you think I need anything other than that and OSHA CFR part 1926 - subpart L?

 

[MiketheEngineer]

We offer complete engineered scaffolds for our customers and so do some of our competitors. While this is not rocket science - some experience (like all engineering) is helpful.

I do design with Safway and it is a good product - but it is not my favorite - for a couple of reasons. If you are doing this for a "real" job - I can put you in contact with local companies that maybe able to help you out. Actaully - those websites I gave you have all the locations and phone numbers - I think.

 

[nuche1973]

There's also QES System from Patent Construction Systems or Harsco Infrastructure as they are now called. This is a ring a pin type system.

http://www.harsco-i.us.

 

[MiketheEngineer]

Yes - that is similar in many respects to the others mentioned.

They all have certain advantages and disadvantages.....

 

[anchorengineer]

Hi Guys,
Thanks for your help. I guess I'm overthinking this. From what I understand I should first make a list of the code requirements and then select a scaffold system that meets those requirements. I'm used to designig every detail. I'm hesitant to use a proprietary system in case it is not available. I don't want a contractor just using what is lying around without it being properly engineered...
any thoughts?

 

[RHTPE]

bclarkeoob, Hopefully you are involved with "scaffolding" (OSHA 1926 Subpart L) and not "shoring or falsework" (could fall under OSHA 1926 Subpart Q). The differences can be confusing, and the factors of safety are very different. Much of my career has involved shoring/falsework for concrete construction and temporary construction supports - there are times when "scaffold" design and "shoring/falsework" design may overlap.

Be careful with the rated loads on any proprietary systems - some suppliers are overly optimistic about their safe working loads vs ultimate loads. You might also check out the Scaffolding, Shoring & Forming Institute (

http://www.ssfi.org/),

which addresses both applications.

What kind of application are you involved in? Where is it located?



Ralph
Structures Consulting
Northeast USA

 

[RHTPE]

bclarkeoob,

You might also check out the California Falsework Manual - an excellent resource. See:

http://www.dot.ca.gov/hq/esc/construction/manuals/OSCCompleteManuals/FalseworkManual(Rev32).pdf

Ralph
Structures Consulting
Northeast USA

 

[anchorengineer]

Between Waco and Safeway I think I have the information I need. It seems that with scaffolding coming in from the far east, US Manufacturers are reluctant to publish load capacities. The whole thing seems a bit too black box for me. Any thoughts?

 

[RHTPE]

Anchorengineer, Having worked in the concrete & temporary shoring field for many years, I can tell you that almost every domestic source of pipe frame scaffold/shoring that has a rental fleet would be unwilling to publish any leg capacity charts, let alone release their charts to anyone except for a specific application that they designed. Most every overseas source for the same that I have encountered tends to be overly optimistic about their products' capacity.

It will depend on your application - are you designing a scaffold application (i.e. a platform for workers and their tools)?

Harsco Infrastructure (Patent Scaffolding) could be one source. I have found Waco to be helpful. Safway sold off their heavy-duty shoring equipment to Symons and it has become mixed in with Symons own equipment. Each had their own load charts which diverged as the height increased. Bil-Jax also fabricated for themselves and others (Waco & Patent?).

Obviously, the taller the stack, the lesser the capacity. As the height grows, the more a scaffold/shoring tower starts to behave as a single post shore, and horizontal lacing should come into play to stiffen the legs. Keep in mind that the lacing must be anchored to a secure support. Screw jack extension also has an impact on leg capacity - some have a very limited range of adjustment and really have little impact on leg load - others have a rather long range of adjustment and a greater influence on leg capacity.

As far as your "Black Box" comment - from the outside looking in, I can agree that's what it appears to be. Having been inside that "Black Box" (in the shoring industry), I can tell you that most domestic manufacturers & suppliers have developed load charts based on load tests. Of course, that testing was done on new equipment. If you're dealing with rental equipment, I can tell you that at least one domestic source arbitrarily reduced leg capacity because of the age & condition of their rental fleet.

Tell us a bit more about your specific application.


Ralph
Structures Consulting
Northeast USA

 

[anchorengineer]

Thanks Ralph.
I have a Medium Duty workers platform that is going to be 125' tall x 60' long. It's going to be sandwiched between 2 buildings. I will have to design an elevated platform for some of the feet that will span between the 2 buildings. The "black box" comment is me just being used to designing every member and connection per the building codes. This scaffolding design work is new to me although I've been on scaffolding for many years now.

With the data I received from one manufacturer of the scaffolding, I was going to tie the frame to the building at each tier and limit the number of levels that could be loaded simultaneously. I was also going to have diagonal bracing at every level on both sides. There will be horizontal bracing at the areas which will have an extension bracket. I'll be working with an allowable load of 3k +/- per leg which has a factor of safety of 4. Screw jack extensions will have to be checked.

As a structural engineer I have to make some assumptions as to the condition of the scaffold. I was going to make notes that the scaffold must be in new or good condition. It must be inspected before erection. It must be erected by a qualified/competent person. There are also daily inspections required as well. I would ass-u-me that the rest is out of my responsibility.

 

[RHTPE]

Anchorengineer, Some additional thoughts:
I was going to tie the frame to the building at each tier and limit the number of levels that could be loaded simultaneously. You say "workers' platform" - for what kind of work? If it's masonry, you should limit the stockpiling of brick/block on the scaffolding. There will be a temptation to load up the platform as much as possible to minimize hook/lift time.

I was also going to have diagonal bracing at every level on both sides. There will be horizontal bracing at the areas which will have an extension bracket. Which direction will the scaffold x-braces run? Parallel with the existing buildings would make sense if you're utilizing "walk-through" scaffold frames. The x-bracing each side will be effective only if you've ensured good member continuity in the 60' direction. I'm assuming that is the length parallel with the existing buildings. If the frames are tied together with continuous scaffold x-brace end-to-end and bottom-to-top, you may not need any additional x-bracing (assuming the scaffold x-braces run parallel with the face of the building).

I'll be working with an allowable load of 3k +/- per leg which has a factor of safety of 4. Screw jack extensions will have to be checked. Screw jacks for scaffolding (as opposed to shoring) are relatively light. Definittely check out their rated safe working load at various extensions. This should be obvious, but don't forget to include the weight of the components that make up this platform.

As a structural engineer I have to make some assumptions as to the condition of the scaffold. I was going to make notes that the scaffold must be in new or good condition. Now that I've unwillingly entered the world of consulting engineering, I have to agree on this. My note regarding contractor-owned equipment reads something to the effect: "All components used shall be new, or shall have been maintained to be in as-new condition." If this is rental equipment and you are not working for the supplier, a similar requirement should be stated. If you are working for the supplier, your professional agreement with your client must address the matter of their obligation to do proper equipment maintenance and supply equipment that meets their rated safe working load.

Hope all goes well.


Ralph
Structures Consulting
Northeast USA

 

[anchorengineer]

Ralph/Mike,
This should be the end (I hope)!

I've received a load table from a manufacturer which gives me the allowable leg loads which is their ultimate/4. From what I've read in OSHA the scaffold must withstand it's own weight plus 4x the anticipated load. Can I multiply the Ultimate Loads by 4, subtract the dead load (say with a safety factor of 2), then take what ever is left and divide that by 4 to get the allowable LL capacity remaining?

For instance:
Scaffold has an allowable load of 2,325 lbs (braced at each tier).
The ultimate load (UL) is 2,325x4 = 9,300 lbs.
Say my DL of the scaffold is 1,578 lbs.
Multiply DLx2 safety factor = 3,156 lbs.
Subtract 2xDL from UL (or UL-2DL) = 9,300-3,156 = 6,144 lbs.
This would be the ultimate load left for LL.
Allowable LL remaining would then be 6,144/4 = 1,536 lbs.

Would this be unconservative? Would you recommend that I just add my DL+LL and make sure it's less than the leg load in the table? Keep it simple?

http://www.anchorengineer.com

 

[RHTPE]

anchorengineer, OSHA 1926.451(a)(1) states:
..., each scaffold and scaffold component shall be capable of supporting, without failure, its own weight and at least 4 times the maximum intended load applied or transmitted to it. That said, your first method (2X DL + 4X LL) meets the requirement. However, for simplicity's sake, I'd use 4 times the total load. If your design is really that close and you need the small advantage, I'd recommend reconsidering your layout. It's a judgement call based on the probability of realizing full Live Load and on the condition of the equipment actually used.



Ralph
Structures Consulting
Northeast USA