Metal Gangways - Marina egress 1

[Bowsers]

Hello Engineers

I am tasked with certifying a large batch (>100) gangways for a shipyard. I feel I've gotten as far as I can on my own, and by searching old threads, so here I am making a new thread.

These gangways were all made in house at the shipyard, with no previous engineering design applied. As I understand it, shop welder putting them together, with an "it'll be right" design philosophy.

This dockyard has the capacity, and now would like to move into servicing military navel vessels as the work becomes available. I would like my employer to retain this contract, and as I am the lead, would like to generate more work for this as well.

I am struggling to find the appropriate design criteria to apply. Nothing seems to be a US Navel standard.

What I have found to date:
2018 IBC References: None, though North Carolina IBC recommends 100 psf
ASCE Planning and design guidelines for small craft harbor: Minor guidance on page 260, nothing suprising (walkway widths, railing height, deflection, 50psf LL)
DNL-VG ST-0358 certification of gangways. This standards orgazniation is new to me. The design guidance seems the most comprehensive, and includes load factors for items like horizontal and vertical loads for operations.
American Bureau of Shipping: Guide of certification for offshore access gangways. Similar design criteria to ST-0358, designed to LRFD. 100 psf LL, operational loads.


Here are my specific questions:
Which design manual or guide governs in the USA for gangways? I have searched navy and coast guard websites and not found guidance. Does anyone have recommendations?
If I am verifying whichever design I go with, would ASCE 7-16 chapter 13 or 15 govern? (Leaning towards 15 as people walk on this).

Thank you

 

[phamENG]

First question - is this for a marina (small craft, maybe places where you tie up smaller service boats) or is this for the shipyard proper with access to and from ships? Big difference.

Also, what are they going to be used for? Will they just be for personnel, or are they large enough to move equipment?

You're outside of the "building code" on this one. The American Bureau of Shipping is probably a good one to use. Have you checked the DoD Unified Facility Criteria? They have one for piers and wharves specifically for naval vessels. I think I remember seeing some information on gangways/brows in there but it's been a few years.

Most I've dealt with use 100psf live load (vertical) and 10 to 25psf lateral.

 

[Bowsers]

Thanks for the reply, pham.

This design is for 'big ships' in a dockyard. I know they recently had a cruise ship in. The cruise ship company required certification of 100 psf LL capacity, which is why we were brought on board. It was a rush job for 3 gangways, and I used seismic lateral loading criteria. Lateral loads were ~21 psf before EL load factors were applied. The shipyard later strength tested the gangway, and it was able to pass.


The shipyard has said these gangways are for personal transport only, as all equipment is typically lifted to the ships.

 

[phamENG]

In that case, you should use 100psf vertical and 25 lateral live load or wind, whichever is more severe. Using seismic was a good placeholder and you're probably used to it out there, but probably not a real design criteria. These are usually hinged at the top and roll at the bottom if memory serves, so you'd have very little actual seismic load develop in it. Another good resource would be the AASHTO pedestrian bridge guidelines. They use 90psf, but I'd bump it to 100psf to make sure you meet the more stringent egress criteria.

If any of these are going to be new builds, make sure you consider vibration. AISC has a good design guide on it with values applicable for pedestrian bridges.

 

[dhengr]

Bowsers:
I don’t know those codes or stds. exactly, but it does seem that the last two would be most appropriate for your situation. If you cited them all in your report, as the best refs. you could find, and then generally picked the most conservative values or approaches from each, you might make up your own set of criteria for the certification, and spell that out in detail. The US Navy has a lot of various, very good, design stds., I’d look a little further there. Ask the Navy if there is a specific std. for this item. And, it is entirely possible that there is not a specific std. for every detail related to every item on a ship or in a shipyard. After all, good engineering and design is really kinda universal and follows the same general rational analysis in accordance with well-established principles of engineering mechanics. I would think about a 400-500lb. concentrated load, a piece of equip. on a dolly, being wheeled up the gangway, along with 3 or 4 – 300lb. workers doing the wheeling. Ask the shipyard what kind of work they intend to do and what their loading criteria would be, and what loading and safety stds. they must comply with. You might take a look at OSHA, re: worker safety stds. etc. and maybe a need for markings for cap’y. and special usage, etc.

The bigger issue in doing this project, and looking good for any future work, might be in coming up with a good, thorough, well thought out plan of attack for such a potential variety of similar items. How do you identify the material specs. that each is made from, or can you pick the lowest common denominator of the mat’ls. used at the yard, at the time the gangway was built? Can you even determine that time of building? Do they have any drafting room plans and specs. for these? Can you group these gangways into four or five common design variations to be grouped together, with various lengths and widths being the only variables in that group, and finally with a few more special exceptions to be dealt with separately? Do you first have to have someone inspect every one of the gangways, just to assess its general condition, corrosion, wear and tear, etc. and report the findings? Then, an inspection list of the important design details, member sizes, material thickness, weld or connection sizes and conditions, so you can start grouping these. Maybe a numbering/tagging system so they can track these gangways from this cert. process forward. Then, a fairly clean and straight forward analysis/design procedure for each group/type of gangway. And finally, a tabulation/listing of each tag no. and its general cap’y. and limitations, or recommendations to bring it up to par. You build on this listing.

 

[Settingsun]

Is there a code for industrial/maintenance access walkways? It sounds as though that's the use. That would be 2.5kPa (50psf) in Australia vs up to 4kPa for a public marina gangway.

100psf for the cruise ship sounds as though they enforced crowd load requirement (egress).

 

[BWCSA]

With regards to DNVGL-ST-0358:

Det Norske Veritas (DNV) is a well-known and respected standards and inspection/certification organization for everything maritime and off-shore. So you could certainly look into their standards and guidelines library (freely accessible) for anything useful.

However, DNVGL-ST-0358 specifically doesn't seem applicable for your certification job. It mentions explicitly (paragraph 1.3 Application): "This standard is applicable to all gangways temporary/permanently installed on a supporting vessel, ship or mobile offshore unit (MOU), and intended to be used offshore. This standard is not valid for ship/MOU– shore gangways."

Maybe you can still find some useful tidbits in it, but I wouldn't mention it as a reference in your report.

 

[bridgebuster]

google UFC 4-152-01, it has the Navy's design criteria for gangways.

Page 15 of the attached article also has design info, slightly different from the Navy's criteria.

 

[phamENG]

There it is. Thought it was in there. And I like that article. Thanks for posting those bridgebuster.

OP- looks like the Navy's criteria is lower than I remembered, and lower than the cruise ship required. I'd stick with the 100psf vertical and a nominal lateral and/or wind load (depending on combination), and vibration for new construction (if existing doesn't display an obvious vibration problem, you may not need to worry too much about it).

I find it interesting that both reduce the live load for calculating a reaction on a floating dock. For an intermediate support it makes some sense as it lets you account for stiffness without discretely calculating it (which could be a challenge considering buoyancy, etc., of a proprietary dock system or existing barge). But for a simple support it's all going there regardless. Unless it's a serviceability thing...it'll usually just have a couple of people on it so oversizing the floating support could result in added flotation at the gangway and a tilted floating dock during normal operation, where a 100psf egress scenario will fall within the float's factor of safety. Sorry. Stream of thought typing...