Winch / Hoist Factor of Safety?

[JoelTXCive]

My Winch/Hoist project is back, and I'm unable to clearly identify what should be a very basic design parameter.

Which is.. What factor of safety should I use for my winch?

I have a well defined load (3,300lbs) and my service level is very low (once a month lifting)

Here are all the dead ends I have come across:

[ul]
[li]I believe I fall under OSHA 1910 for Overhead & Gantry Cranes. OSHA does not mandate a factor of safety (as best I can tell), they just refer you out to ANSI/ASME B30.2 (Section 1910-179(b)(2))[/li]
[li][/li]
[li]I do not see a specific factor of safety in ASME B30.2.[/li]
[li][/li]
[li]I also do not see one in B30.16 (Winches) or B30.17 (Overhead Cranes).[/li]
[/ul]
[ul]
[li]I have found some required safety factors in ASME's Below the Hook document (BTH-1-2017), but this is just for rigging and not the actual lifting device.[/li]
[/ul]

I have heard talk of a 5:1 safety margin for cranes and lifting mechanisms, but have not seen that value in print anywhere.

Can anyone help? I must not be looking in the correct spot; or I am missing something.

Surely I am not the first person to design a winch and mount?

 

[JStephen]

I'd be kind of surprised if there was a single value of factor of safety used. It's kind of like asking what the factor of safety of an automobile is.
But, for example, see this page:

https://www.cranetech.com/blog/mobile-crane-stability-part-4-adding-it-all-together/

Where it states "For this example, we can use a typical hydraulic truck crane, which is based on a maximum rating of 85% of its tipping load." IE, factor of safety for overturn is less than 2.

 

[JoelTXCive]

I agree with you JStephen that there should be different factors for different scenarios.

I would think there would be some research somewhere that says: "common industrial hoists/cranes have a XX to 1 safety margin."

It would be nice to have something in writing that I can hang my hat on when asked about the safety factor.

I did locate the 5:1 ratio. It is an OSHA requirement, but it's in the construction section 1926. I do not think it would apply to a permanent winch/crane.

 

[GC_Hopi]

Are you designing the structure support a winch/hoist or the actual winch/hoist (mechanical design)? In the live load chapter of ASCE 7 it has information on load factors but I would consider these for the structure. ASME would be the experts for actual winch/hoist design.

 

[r6155]

See ASME B.30 series.

Regards

 

[JoelTXCive]

GC Hopi - I will be doing two things: 1) Selecting the winch capacity, and then 2) Designing the mount for it.

The winch will open and close flap gates for maintenance. We have an existing steel platform that we are going to modify for the winch mounts.

R6155- I've tried the ASME B30 series. They are mostly about safety concerns after a winch has been installed. They discuss maintenance schedules, physical clearances and other related items. As best I can tell, the only ASME document that makes any true design recommendations is the 'Below the Hook' document.

Below is a cross section of what I'm working with.

 

[JoelTXCive]

 

[r6155]

You are very confused. This is the first time I've heard of design factors applied after installation.
Sorry.

Regards

 

[JoelTXCive]

The work is for a municipality. The steel platform is 25 years old.

They had funding for the flap gates last year; and did not want winches. This year, they have decided to install winches.

Generally speaking, we do not do design work until the client requests it.

 

[CrabbyT]

Why not just purchase a 2 ton winch? Or a 3 ton winch if wind is a concern?

Seems like an off-the-shelf item would be a lot more cost effective than a custom winch, and it would have already been designed with all the relevant safety factors taken into account.

 

[GC_Hopi]

You can use the load factors from ASCE 7 as a minimum. ASCE 7 states to use the rated capacity or stalled load of the hoist whichever is larger as a live load. I would also review the corps of engineers document ETL_1110-2-584 Design of Hydraulic Steel Structures. It is free online and has load factors along with load combinations. The bureau of reclamation might have a design guide as well.

 

[JoelTXCive]

CrabbyT - Yes, I think you are correct. We are attempting to purchase an off the shelf unit. I talked with a winch company this morning and requested info on 10,000lb winches, which will be a 3:1 safety margin.

I will then make sure my steel platform and modifications can handle that load using LRFD methodology.

GC_Hopi - Thank you for the Army corp reference. I will download.

 

[EdStainless]

Watch out about oversizing the winch. You now have to design the structure for the stall load of the winch, plus some margin.
We were lifting steel coils. because of the equipment size they would never weigh more than 5800#, we used hoist rated at 4T and even though it was designed to be strong enough to handle 2.5 times that it was clutch limited to lifting the 4T. The hoist frame was designed at 12T. We made sure that each part exceeded the gross rating of the part attached to it.
Will people be working under these?
If so can you build in a hard lock to hold them or will you rely on the winch?

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[JoelTXCive]

Ed -

Yes, We will lift up the 8'x8' gates and then workers will drive a small bobcat through the box culverts to clean out any muck & debris.

We have discussed a back-up restraint, but have not come to a decision. Perhaps a secondary chain or wire rope that can back up the winch.

I'm familiar with 3 other locations and they rely on the winch only to hold the gates open for maintenance.

When talking to the winch consultant, they said they were going to provide me information along with their recommendation on the brake system.

 

[SJBombero]

I think ASCE 7 4.9.1 is applicable rather than 4.6.4.

4.9.1 General. The crane live load shall be the rated capacity of the crane.

Using the stall load of a winch would be a huge overdesign. Typically all cranes can pull themselves down if you load them up enough since the lift rating is not based on the capacity of the motor to lift but rather the capacity of the motor to accelerate the load to reasonable lift speed.

I would think that relying on the winch only to restrain the door during maintenance would violate OSHA regulations (and basic common safety) regarding working under a lifted load.

 

[dik]

Also depends on the juridiction... for many items lowering things down the 'shaft' the mines act may require a SF = 10.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[JoelTXCive]

PVChabot - I'm very open to having a back-up safety, and I think my bosses + the site operator would be too.

There is some crazy stuff out there...on some facilities they use automotive winches to lift gates, or chains attached to back-hoes to raise the gates for maintenance.

I wonder if I could have a 2nd chain that could be tightened and secured after lifting the gate with the electric hoist.

I'll see what the Winch company rep comes back with. It is definitely an area that we will look at.

 

[dhengr]

JoelTXCive:
In your X-section, where is the gate hinged, that doesn’t show up on the drwg., and what are the hinged linkages on each side of the gate for? The X-sec. does not seem to match the photo, why not, and which is right? You don’t need a 10k winch to lift a 3.3k load, you are piling a FoS on top of another FoS. I agree with JStephen…, “I'd be kind of surprised if there was a single value of factor of safety used.” and I like his analogy “It's kind of like asking what the factor of safety of an automobile is.” The winch people already have a FoS in the design of their own equip., for their confidence in their own design, so it will already lift much more than their rated load without failing. Ask the winch manuf’er. about this, you are not talking about lifting double/triple the rated load 10 times a day. Do you really clean those 8x8 box culverts out “once a month lifting” (28APR21, 19:32)? This relates to the duty cycle per day or year, and the life of that equip. If you want some FoS for your own overall design and mech./elec. equip. package, for proof of deign to the client, consider testing the system to (125%)(3.3k). You will find that ‘125% of the rated load/lifted load’ as a final testing value, in a number of places in the ASME B30 stds., this is a fairly common proof testing loading for lifting equip, when structural or mech. equip. are the limiting factors. The 85% of lifted load number for stability of a crane has been around for a long time, but doesn’t really apply here.

Depending upon the exact situation, I would look at buying 2 or 3 winches about 2 or 3 ton cap’y. Your 5t (10k) winch is really expensive overkill. I would put these winches on little railcars, on tracks, on longitudinal beams, up on your existing platform/deck. These can be moved to track stops over each gate, since you are not likely working on all gates at once. I would put an elec. power supply stand btwn. two (every other) gates, to serve those two gates with power and control. This type of system will likely save your client in first cost, and in maintenance of excess equip. The max. lifting load would appear to be during the initial opening phase, so position this track system for best advantage at that phase of the work. This same railcar/track/winch system might be used for gate maintenance and replacement lifting, so consider that as a potential future use, and price advantage of your offering. That same winch could run a second wire rope drum, with an unloaded safety cable, attached to the same lifting shackle on gate. This wire rope would just be pulled up to the deck as the gate opened, and then through a fixed loop at its top end, it would be tied off to a fixed spot on the deck or the railcar. Put a hinged cover box over the winch to keep it out of the weather when not in use, but let it breath.