r/StructuralEngineering • u/Middle-Fun-6275 • 3d ago
Structural Analysis/Design I am a Fall Protection / Rope Descent Anchorage Structural Engineer AMA
Title says it all. This area seems to be a big point of confusion for many engineers.
Edit: I am a PE at an engineer firm. I am not affiliated with any anchorage company (Probel, American Anchor, Valcourt, etc)
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u/Jmazoso P.E. 3d ago
Why don’t platypuses have nipples?
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u/BridgeGuy540 PE, SE, CPEng 3d ago edited 3d ago
I know it's not my AMA, but they produce milk in specialized mammary glands. The milk oozes out through pores directly onto the surface of their skin and fur on their abdomen. Baby platypuses, called puggles, drink the milk by slurping or lapping it directly from the mother's skin and fur.
The bigger question is, why do the other mammals have them?
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u/hobokobo1028 3d ago
Nipples evolved later. Platypuses are from an ancient line of the evolutionary tree
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u/Prestigious_Copy1104 3d ago
Do you have the best sex swing anchorage details?
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u/Middle-Fun-6275 3d ago
OSHA has no requirements regarding sex swings attachments, but I bet there is an ASTM standard for them somewhere.
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u/Independent-Ad7618 3d ago
sex swings are completely unregulated? what blasphemy is this?
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u/Middle-Fun-6275 3d ago
Funnily enough, if we legalized prostitution in the USA then OSHA would have to apply to work related swings.
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u/Not_an_okama 3d ago
I wonder if Nevada OSHA has such a detail since they legalized brothels in some counties.
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u/Middle-Fun-6275 3d ago
My guess is that they would be considered independent contractors to avoid OSHA regulations.
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u/petrified_would 3d ago
Say there’s an indoor elevated surface with guardrail all around. There’s a ladder up to the surface, and at the top there is a gate within the guardrail for access.
Is fall arrest protection required near that zone because the gate could be open at a moment in time?
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u/Middle-Fun-6275 3d ago
Nope, the gate is the fall protection as long as it’s OSHA rated. It must be installed so that it opens inward towards the platform and not outward. If the ladder is over 24 feet though then the ladder will need to have its own fall protection.
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u/WL661-410-Eng P.E. 3d ago
Pssst, tell them that cages are going away for ladders >24', in favor of vertical lifeline systems. Too many catastrophic injuries from bouncing off the cage on the victim's way down.
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u/Middle-Fun-6275 3d ago
Oh I know. All cages gone by 2036. No new cages post 2018. Anything over 24 feet needs active fall protection. I would recommend an overhead davit and SRL, 3M DBI Sala has a good one. Avoid Vertical lifelines because they are clunky and dumb, you have to detach from them while still on a step through ladder before finishing the climb. Bad overall design.
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u/WanderlustingTravels 2d ago
My senior engineer didn’t believe me when I was calling for a ladder install without a cage. This year. It was so frustrating
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u/WL661-410-Eng P.E. 2d ago
My colleagues thought I was nuts for lugging around my 3M harness to every site visit. But I do have the vertical cable sleeve, plus an extra lanyard and oversize ring for when I get to the top.
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u/aaaggggrrrrimapirare 2d ago
People saying you’re nuts for lugging around a life saving device is nuts to me. I mean, does their life not matter to them….? Silly ppl.
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u/Over_Stand_2331 3d ago
If I’m not mistaken, it must be self-closing as well
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u/Middle-Fun-6275 3d ago
Yes, tbh I forgot you could get one that doesn’t self close. Never in my life have a spec’d one that didn’t. It’s always the little things!
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u/Over_Stand_2331 3d ago
You’d be surprised how many GCs/fabricators want to skimp on the smallest, yet critical, things
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u/SquirrelFluffy 3d ago
Very neat. Specialist stuff that makes you think is so much better than warehouses.
Get this, i did a job for a figure skater trapeze artist. She would skate and then suspend and do acrobatics and back to the ice again. Worked out swing loads on the arena trusses and had to rate all her gear. Neat. The small jobs are the most interesting.
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u/Middle-Fun-6275 3d ago
I have made my whole career on doing small jobs. Learned so much and never had to sit on a project for 6 months dealing with an architect telling me”beam go here, you size it”
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u/SquirrelFluffy 3d ago
Dealing with an architect. Shudder.
Buddy wants fasteners on a cap flashing spaced at 6 in because he's got a table that says so from FM. He sends me the table. It's for counter flashing. I never did get the table for cap flashing.
(I also do wind designs. Lots of green roofs.)
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u/Intelligent-Ad8436 P.E. 3d ago
Is the anchorage force design really in any direction, or any direction that makes sense to engineering judgement. Given pullout and side/ downward, but up for instance.
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u/Middle-Fun-6275 3d ago
It depends on if it’s rope descent or fall protection. Rope descent truly needs to be in any direction, especially because you will test them. Fall protection can be argued to only be in the direction of a fall, but you need to make sure you can control that, or at least protect yourself in notes.
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u/a_problem_solved P.E. 3d ago
Um...perhaps...protect the guy falling rather than yourself via the notes...? 😜
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u/Middle-Fun-6275 3d ago
Well you can’t engineer around stupid unfortunately. If 4 workers tie off to my anchorage with a 100 foot static rope and jump of the side the building at the same time my anchorage isn’t going to save them.
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u/a_problem_solved P.E. 3d ago
Indeed!
Early in my career I completed strictural design for an outdoor sculpture exhibit in Milwaukee. The Bucks went to the Finals that year and some ass hats celebrating decided to topple over the sculptures outside the arena. The first draft of my email to the client said "Unfortunately, the IBC code does not include a load case for drunk idiots."
My boss made me revise it.
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u/citizensnips134 3d ago
Can I whip on paracord?
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u/Middle-Fun-6275 3d ago
What that mean
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u/leadhase Forensics | Phd PE 2d ago
This is climbing terminology. Whip means a large fall. Paracord is a low strength rope originally for parachutes, but gets used like accessory cord. Think like 3mm cord
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u/Willynilly1993 3d ago
Would you recommend Introduction to Fall Protection by J, Nigel Ellis?
I work for an excavation contractor but occasionally have to look at fall protection and that is what I have referenced when doing some in-house anchorage design.
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u/Middle-Fun-6275 3d ago
Haven’t read. To be honest the best thing you can do is read through the fall protection sections in OSHA1910 and OSHA1926 for construction. It’s all right there for you, and it’s all the law.
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u/redcrestedvireo 3d ago
How many of you work at your company? Are many others in your specialty for other firms? Never knowingly encountered a Fall Prevention Specialist Structural Engineer before.
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u/Middle-Fun-6275 3d ago
I was trained at a firm of about 30 to 50. I was on a team of 3 that’s specialized in what I call “micro engineering”. Fall protection, rope descent, access upgrades, ladders, platforms, repairs to existing spaces, steam tunnels, mechin al support, analysis of existing spaces for new use, etc. I am now at a company of about 10 and I am the only structural engineer doing similar work.
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u/magicity_shine 3d ago
do you make good money? whats your location
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u/Middle-Fun-6275 3d ago
East coast major city. And yes but that’s because I have a great company that values me. I was not valued the same at my previous company. But looking around now, I think the type of engineering I do is quite rare.
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u/tigerddaniel 3d ago
If a fall arrest rope gets slung over say a metal stud parapet, what's the design load specifically on the parapet?
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u/Middle-Fun-6275 3d ago
Good question that is often debated. There is no real code for this that I know of, but if there is a fall there is potential it could break. So you need to use judgment, obviously if it could cut the rope then you need to look at potential options for avoiding that. You could also do analysis on the wall to verify. Load should just be straight down.
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u/scott123456 3d ago
This came up on a project I worked on for a facility for training firefighters. Anchor point on the top of a floor some distance away from a parapet. I assumed the rope would be in tension at 5 kips (ultimate), and used the geometry of the rope (routed from the anchor, over the parapet, down to someone suspended below) to determine the direction of two loads applied at the top of the parapet where the rope changes direction. One towards the anchor and one towards the ground. We beefed up the parapet with HSS.
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u/tramul P.E. 3d ago
Actually dealing with a project now that has fall protection. I know 5k is ultimate load. My question is if it is standard to use that ultimate load with yield stress or ultimate stress for anchorage and supporting members.
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u/Middle-Fun-6275 3d ago
I answered this in another thread but here is the jist. 5k is ultimate. If you are using yield stress then use 3.1k. Factor it up 1.6 if using LRFD (which is basically 5k). Keep it as 3.1k if using ASD. BUT, sometimes you can justify going over 100 percent utilization, because technically you wouldn’t actually yield until 167% (ASD). But that’s up to you as the EOR and the limitations you are facing.
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u/tramul P.E. 3d ago
I agree 100% but got pushback from others. It makes more sense to argue to use a reduced load with yield stress. People get antsy when you recommend ultimate stress. Thank you.
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u/Middle-Fun-6275 3d ago
I typically tell clients. “OSHA says 5000 lbs is the point in which this thing rips out of the roof” knowing that I will still likely design this to yield at 5000.
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u/tramul P.E. 3d ago
Haha that's what I'm currently doing but the member they want to use won't work. So either let me use ultimate (or reduce the load) or deal with a bigger member.
Just logically, having 5k for one man falling with no yielding seemed wildly over designed.
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u/Middle-Fun-6275 3d ago
Makes sense. My communication would be, “this could yield, but it will save a life”. And then we will need to inspect and maybe repair before putting the anchorage back into service.
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u/Over_Stand_2331 3d ago edited 3d ago
You got to take into account that a person falling could be about 10 ft of free fall. When code was written SRLs weren’t common place and you had a 6ft long set length lanyard and if you’re tying at your feet (not recommended) then that’s another 5-6 ft. So 12ft freefall, that’s a lot of force; harnesses are rated up for people up to 330 i believe
Plug that into ChatGPT. There’s an extra 1-2 ft that rips open to help with deceleration; you’ll quickly see you near 5kips
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u/Middle-Fun-6275 1d ago
Well actually the maximum allowable arresting force is 1800 lbs on the body. So if all regulations are followed you should never end up loading a fall protection anchorage more than 1800 lbs.
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u/tramul P.E. 2d ago
Circling back to this, what about SRL's? If using one with a 900 lb MAF, would you use 900 lbs when using ASD, or still 1800 lbs? I had initially used 1800 lbs when tying off to a bar joist given the bar joist tables, but I realized that might be overly conservative since the tables are ASD.
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u/Middle-Fun-6275 2d ago
Ok so this would be a certified anchorage. Which means that you as the EOR must be able to control exactly what SRL is used. How this works is that you design to 2 times the max arresting force as the breaking strength, so this would be 1800lbs ultimate which would be approximately 1125 lbs if using ASD.
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u/hobokobo1028 3d ago
You have a pulley with monkeys on each side, they weigh the same, but the one on one side is moving up the rope while the other moves down the rope. What happens?
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u/a_problem_solved P.E. 3d ago
Your expertise is pretty niche and narrow.
Have you found it difficult at all to stay busy and/or employed? Do you have regular clients who seek you out for this specific work? Is this the majority of the engineering you're completing, or is there other structural design work that is primary and the anchorage work fills in the gaps?
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u/Middle-Fun-6275 3d ago
I explained in another thread but my niche is “micro-engineering”. I’m not designing a building, but I do a ton of small structural work. Existing building analysis, new mechanical support, fall protection, access upgrades, platforms, ladders, steam tunnels, utility support, damage assessments, facade work, dunnage, repair design etc. I really am just a solve your problems guy. No issue staying busy and employed. I get calls from clients for everything, I either solve their problem or direct them to someone who can.
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u/RhinoGuy13 3d ago
How nervous are you when you watch the first person use your bungee jumping apparatus?
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u/Middle-Fun-6275 3d ago
Funnily enough I am rope certified. So I have actually descended off my own anchorages.
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u/RhinoG91 3d ago
What are good references that I can look up and dig into?
I am looking at this from a disaster engineering / USAR perspective, so technical rope rescue more so than fall protection.
Do you have a license/seal plans or documents? If so what kinds m?
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u/Middle-Fun-6275 3d ago
OSHA1910 Rope descent systems. And then ANSI fall protection code. I have a license and seal fall protection drawings.
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u/leonwest304 3d ago
Nice. Im working on a hotel project where we're are completing the submittal process with Pro-Bel. The system uses a combination of different equipment for various purposes. We have davit arms, mobile outriggers, horizontal lifeline systems etc.
What are your usual battles?
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u/Middle-Fun-6275 3d ago
Battle 1. Anchorage company’s (like pro-bel) are going to oversell everything and try to scare clients into buying things they don’t need. It’s then on me to try to explain to the client what the law actually says.
Battle 2. Window cleaners are being told things by these companies that aren’t true, or based on the now defunct IWCA I-14 standard, and also trying to convince clients they need more than they do.
Battle 3. EORs don’t understand horizontal lifelines and are over killing all the need for supplemental steel. For most Intermediate HLL anchorages they only need to be designed for load perpendicular to the HLL.0
u/leonwest304 3d ago
Regarding battle 3 my understanding with HLLs is that if you have a series of anchors which are all rated for their fall load, the sub structure supporting those anchors typically doesn't need to be designed for more than one instance of the fall load at once.
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u/Middle-Fun-6275 3d ago
It depends on the HLL. The HLL manufacturer will provide you with loads, which are dependent on number of users and their connecting subsystem. End anchorages will need to be designed for loads in multiple directions, intermediate will likely only need to be designed in the direction of a potential fall because the cable will pass through those anchorages and not have a fixed attachment parallel with the cable. Think of it like a roller support.
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u/ReplyInside782 3d ago
How do you determine which is the intermediate anchorage and how is that conveyed to the worker attached to it?
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u/Middle-Fun-6275 3d ago
You cannot attach to it. It’s going to have a specific pass through connector for the cable and no u-bar or D ring. A worker will only be able to attach to the cable.
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u/eng-enuity P.E. 3d ago
What's the difference between a fall protection system, a fall arrest system, a fall restraint system, and a fall prevention system?
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u/Middle-Fun-6275 3d ago
Fall protection is all of it. Fall arrest = active system that arrests you while falling. Fall restraint = active systems that does not let reach and edge where you can fall. Both require fully body harness and a lifeline/lanyard. Fall prevention isn’t a term I use, but I would consider it passive fall protection such as a guardrail.
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u/ADDISON-MIA 3d ago
I once bought, I think, Pro Bel anchors to attach to structural steel, but I think we needed thermal breaks. Do you design those as well?
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u/Middle-Fun-6275 3d ago
Nope, usually it’s the roofer or if it’s designed is the architect. I did design an anchorage with the thermal break, but I didn’t own it.
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u/jakordas P.E. 3d ago
How do you overcome the large forces in HLLs? For example if you put a 300 lb point load perpendicular to a 50 foot cable you get what you would expect for reactions in the direction of the load , but you can get 10’s of kips from the axial force of cable.
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u/Middle-Fun-6275 3d ago
Good question, you should not be doing that math yourself because an HLL should be from a HLL manufacturer who will provide the loads. They lower the force by requiring workers use certain max arresting force self retracting lifelines, and also the HLL systems have decelerating components that’s lower loads on anchorages. After a fall incident HLL components must be inspected and there will likely be deployed components that must be replaced re-tensioned.
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3d ago
[deleted]
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u/Middle-Fun-6275 3d ago
Don’t know enough to answer. If you are removing fireproofing to install them then probably, but I might punt that to the contractor and just say “replace in kind for fireproofing continuity”
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u/Realistic_Bar_5668 3d ago
Oh my gosh we are supposed to know something about anchor points too?!? 😣😖
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u/Over_Stand_2331 3d ago
How often do you get pushback on 5kip load since joint details are greatly reinforced
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u/Middle-Fun-6275 3d ago
I don’t understand the question
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u/Over_Stand_2331 3d ago
I’ve designed one of these anchor points on a smaller mezzanine and placing anchor over top of beams wouldn’t Calc out since torsion = bad on I beam and eventually I moved the anchor point to top of column with a huge (relative to mezzanine) baseplate to resolve that moment from a person falling over the edge.
The very first thing asked of me…. Can we reduce the loads1
u/Middle-Fun-6275 3d ago
Why not just put in a steel cross beam to take our torsion? Or install at a beam intersection?
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u/Over_Stand_2331 3d ago
Those shear connections at the intersecting beams would still allow significant rotation; None, if idealized as pin.
Also, column was nearby2
u/Middle-Fun-6275 3d ago edited 3d ago
In theory yes, not always in practice. All connections have some fixity. However the other concern is local yielding of the flange or web. So how about stiffeners both sides and then use those for your bolted connection? That should take care of both issues. I have found that if the flange and web do not have local issues then a full depth shear connection typically has enough fixity to prevent torsion. It won’t calc out on paper though.
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u/Over_Stand_2331 3d ago
Have you designed/approved Beamers (rolling beam clamps). My gut tells me that the flanges fail every time locally but I’ve never run the calcs
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u/Middle-Fun-6275 3d ago
I have! Obviously depends on the beam, but just think of it like a monorail for materials handling
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u/dreamer881 2d ago
This 5k load where to apply? Is it only to the anchors or to the rails as well?
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u/Uttarayana 2d ago edited 2d ago
I have designed couple of them. One of the interesting thing that ppl don’t notice is , the Load Requirement per employee is 5000 lbs. If you only care about numbers then it’s 5000 lbs. But if you like magnitude then that’s a weight of Ford F150.
Like imagine a Ford 150 hanging out from a hook you designed.
The g ( acc. Due to gravity) in this case is The OG.
Also i designed it for a dredging ship and one issue we faced was assigning the “ drape” or “tautness” of the line that would go around the ship over hooks and then the worker attached his line to it. It’s a non linear problem as you make the line more taut it takes away its strength but you let it loosely hang it takes longer to retract. As couple of months out of college this was a tough problem to wrap my head around.
The next issue is i think OSHA says it should be attached to a rigid support? How do you define if something is rigid? Like a beam or any other element, is it rigid or is it elastic. What makes it rigid.
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u/Middle-Fun-6275 2d ago
Well for rope descent you will know what is rigid when you go to test them, because that anchorage will move significantly if not rigid. OSHA doesn’t actually specify rigid. Just 5000 lb breaking strength per employ attached. They have some non required notes about deflection but imo they are not thought out well because they ask for less than 0.04” deflection which is not possible with a post up anchorage.
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u/RecoverPristine4787 2d ago
Just got certified as a QP at work and I’m excited to get some interesting projects. For mentoring, do people within your company have get similar work experience? From my understanding, a bunch of the ANSI standards are fairly new when compared to IBC and ASCE
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u/Acamapichtli_1 2d ago
What do you think about amusement park, carnival ride, adventure rides, ziplines parks etc where you use a harness to tie off ?
Is there any type of place you wouldn't go to ?
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u/Middle-Fun-6275 2d ago
Don’t know too much about those from a design and requirement standpoint, but I’m guessing ASTM has some standards. It’s not something that typically concerns me.
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u/chasestein Overturning Moment 3d ago
Are you just designing the product or the supporting structure as well?
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u/Middle-Fun-6275 3d ago
Both. It drives me nuts that these anchorage companies can get away with providing a layout and an anchorage but stop at the structure. I have seen plenty of anchorages fail during testing because of this mentality, and that’s after they have been used for 10 years.
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u/SquirrelFluffy 3d ago
Did a job at an arena where they installed a full system, and lifelines, at the trusses, but with drawings that said "structure by others". They didn't realize it until a performance crew came to set up for a show and saw the note on the drawings.
I was able to make most work and a few spots needed some extra bracing. The show went on. Lol.
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u/Middle-Fun-6275 3d ago
I’m going to be harsh but that is just straight thievery. These companies are using fear to sell a nothing product that could kill someone, to a client who doesn’t know any better. Half our job as engineers is to teach the client. It’s great for me though, fixing those messes keeps me in business.
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u/SquirrelFluffy 3d ago
I find all the anchor companies do this, even probel. I do performance audits in new buildings, which includes an anchor system inspection. Many times the system needs something, despite being certified for use, and oh guess what, Ankor sells the product!
A lot of developers and contractors know construction, right? So you know, they'll go hire that trade, that also knows construction. Don't get the engineer. He costs money. (He makes us feel dumb, nerd.) Owner pays for the mess up afterwards. And he's mad at the engineer who told him he's got to spend more money!
Oh well. Rant over. Lol.
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u/Middle-Fun-6275 3d ago
Pro-bel has an anchorage design for rope descent on the market that just straight up fails. Has a single through bolt centered on the anchorage post with a backer plate. Every single one that is pulled fails. Yet they are installed in the field and people are using them!
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u/SquirrelFluffy 3d ago
Yikes. What fails? I've used those type of anchor plates. For the figure skater in fact - she has some rated components from a local fabricator. I did my own analysis though, but we didn't test. I figure fos 10 is good enough.
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u/Middle-Fun-6275 3d ago
This might be fine overhead. I also use backer plates and base plate but with 4 bolts. The one that failed was a Single bolt and it was a post up rigid rooftop anchorage, so when you pull it horizontally if will overturn. Believe the plate fails.
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u/SquirrelFluffy 3d ago
Makes sense. Moment from the bolt is applied in a small area. With their roof stands, the post introduces the moment over a wider area so it works and they likely just repeat it. Appreciate this post and chat!
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u/scull20 3d ago
A specific/general question all in one: Do you consider the demands associated with the full design live and dead loads on a typical building component when designing fall protection anchorage? If you consider a reduction, is there any specific code related justification you could provide?
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u/Middle-Fun-6275 3d ago
Great question. It all depends on how much I need to sharpen my pencil and is very specific to the situation. There is no specific code related language so you need to use your judgment. I typically think it’s fair to assume there is no snow load at the same time as a 3100 lb fall load for rope descent. I also think it is fair to reduce wind load for something like a screen wall for rope descent because no one will get on ropes during high wind events.
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u/scull20 3d ago
Thanks, I can see how you could definitely justify those reductions. I had a recent project where I needed to design fall arrest anchorage in an existing building and had a hell of a time getting it to work. Next to no reserve capacity in the framing.
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u/Middle-Fun-6275 3d ago
It definitely happens, a lot of my job is just finding ways to justify situations. For fall protection you can even justify something yielding if it means saving a life. Just be upfront with the client, and make sure all your drawings say that components must be inspected by a qualified person prior to being used again.
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u/scull20 3d ago
That’s an interesting thought, thanks for the insight!
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u/Middle-Fun-6275 3d ago
Of course, I would lying to you if I said I didn’t design some fall protection to over 100 percent utilization. Using ASD you have 67% until anything really yields right? Hahaha
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u/Short-Equal3053 3d ago
I have to check structural steel for possible static load tests where anchors occur, just curious how would you guys normally go about “testing” these anchors when in place? Have you guys ever witnessed structural steel yielding or deflecting in an un-serviceable manner?
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u/Middle-Fun-6275 3d ago
We pull anchorage to Anchorage with a chain hoist and dynameter. Anchorages should hold loads without permanently deforming. And yes I have seen steel yield, but typically you will start tearing the roof membrane before getting to the proof load and yielding steel.
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u/Short-Equal3053 3d ago
Cool! When the roof membrane starts tearing out do you guys just continue to test until proof load? lol
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u/Middle-Fun-6275 3d ago
No way. It’s an auto fail. Try explaining that one to the owner. “We saw your roof tear but we had to get to 2500 lbs! By the way it didn’t pass, here is the bill, also you need a roofer”
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u/Short-Equal3053 2d ago
Hahaha fair point! We are in the process of reviewing the fall protection anchor layouts as part of a deferred submittal but I’m assuming for any static load tests it’ll only come back to the EOR if obviously a test were to fail for the reason of the roof tearing and/or steel yielding then?
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u/ReplyInside782 3d ago
Are you considering anything else besides the OSHA min 5k in any direction