Design a connection plate between two wooden plates and ladder for access 6

[patstructural]

Hello everyone,

I am a recent grad in Ontario (Canada) working for a company where I am their first hired structural engineer, they have other engineers.

I have been tasked to design a platform (more like a plate) between two wooden plates, see attached image (blue highlighted area is where the plate will be, for maintenance purposes; and ladder is meant to provide access to the elevated wooden plates). I designed a slab, beams, columns in school and even a building in my last year so I am comfortable with the knowledge/experience I gained and I am sure it helped. However, I would like to confirm if my design/analysis approach for this task is correct or not, since I have no experience designing neither at school. Additionally, the task is for a US project and I believe I will have to use their standards/guidelines/regulations.

1. Plate considerations:
Design
a. Location
- Seismic? _ I don't think this should be an issue but could be wrong.
- Code requirements? (US equivalent of CSA Design)
- Avoid clashes/interferences
- Dimensions (28"x14"x5")

b. Capacity
- Max loading conditions at supports
- Construction joints (bolted)

c. Use
- Anticipated loading conditions on platform (check code!!!) - DL (self-weight) + LL (300 lbs from maintenance crew)
- Protective railings?
- Steel/aluminum/wood to wood? _ I took steel and wood design courses but I'm more comfortable with steel.

Analysis
- Slab
- Slenderness _ Isn't this normally a column consideration plus the steel plate is fairly small where I don't think a slenderness ratio matters.
- Min bolts
- R factor? _ Based on research, this is related to seismic. I took a seismic course but I didn't cover this.
- Deflection
- Drift (caused by seismic)
- Buckling _ Since buckling is from lateral or compression loadings at supports, I assume this is a non-issue.

2. Ladder (Fixed) Considerations:
Design
- Material (steel/aluminum?) - slip resistant
- Dimensions (The width of the ladder should not be less than 600mm?; height from floor to wooden plates = 5' 6")
- Loading condition
- Supports (welded between rungs and side rails; bolted/anchored at bottom and top)
- Codes and guidelines (OSHA + others)
**Do not use a metal ladder when working with electricity or electrical current

Analysis
- Moment frame
- LTB (Lateral-torsion buckling) - lateral loading

OSHA Fixed Ladder Requirements
- 10" minimum and 14" maximum spacing from centerline to centerline of rungs. Note: ANSI A14.3-2008 calls for exactly 12" spacing of rungs (the first rung can be up to 14" from the floor surface.)
- The minimum clear width of rungs on fixed ladders shall be 16". Note: The International Mechanical Code 2018 (306.5.4) calls for a minimum of 18" between rails. This width increases to 24" clear at the top of the ladder where the side rails extend 42" above the deck.
- For 90 degree (vertical) ladders, there shall be 30" of clear space on the climbing side.
- Fixed ladders shall not have a pitch greater than 90 degrees.
- Extend 42" above the landing or access level? (check)

I would be happy to provide any additional info to the best of my abilities. Thanks for the help.

 

[JStephen]

My guess on how this would normally work would be that somebody out in that shop would slap a piece of steel or aluminum checker plate over the gap, put a bolt in each corner, and call it good, without ever involving any engineering.
I'd check back with the supervisor and try to nail down just exactly what they want. You could spend a lot of time designing handrails, handrail anchorages, checking the whole thing for overturn, etc., but it would be kind of uncommon to have handrails on something like that in the first place.

 

[WesternJeb]

My advice is to find another firm with a mentor as soon as you can. I am sure you are capable of a lot of things, but you don't know what you don't know.

 

[human909]

My advice is to find another firm with a mentor as soon as you can. I am sure you are capable of a lot of things, but you don't know what you don't know.

I think in general this is excellent advice.

Though I'll put forward my experience as a counter point. I joined an engineering firm where I was the only structural engineer. It gave me fantastic opportunities that accelerated my learning and my career. However it was certainly baby steps to begin with and I did seek out an external mentor.

If your firm has hired you expecting you to perform full structural design and analysis from the get go unaided then they are naïve at best or simply irresponsible.

 

[patstructural]

Thank you all for the help.

I'll be careful moving forward if they want full structural design and analysis without the supervision of a qualified mentor.

I will discuss my findings with my superior (P. Eng. in chemical engineering) at work and decide what our course of action should be.

 

[dik]

I feel for you... looks like you have been tasked with a problem that appears to be simple, but it actually fairly complex. The above advice is good. I was thrown into the 'deep end' early in my career; it was an adventure, but times were different.

To design the plate, assuming it's checkered plate, there is a spreadsheet by Alex called Flrplate (attached). I've attached a copy of my shop drawing review notes for ladders to give you a bit of an outline of what you should be looking at. I modify the notes to suit the project, and some of them are not applicable (not trying to confuse you). You need to determine what standard is applicable for your project.

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/raw/upload/v1702915385/tips/FLRPLATE13_urduui.xls[/url].

LADDERS:
-DESIGN LOADING:
DL AND LL FACTORS FOR LADDERS, AND GUARDS BOTH ASSUMED TO BE 1.0;
RUNGS AND ACCESS STAIRS 1.32KN (300LB) AT ANY LOCATION WITHIN A 10’ HEIGHT; AND
LADDER RAILS 4.448KN (1000LB) VERTICAL AT ANY LOCATION;
LADDER LOAD IS SHARED BY 4 FASTENERS;
LADDER DEAD LOAD SHALL BE LESS THAN 75 LBS PER FASTENER;
STEEL GRATING TO BE DIAMOND GRIP STRUT® GRATING BY MARCO, TYPE 1-1/2” x 12 GA OR EQ.;
LADDER RUNGS SHALL BE GRIP STRUT® LADDER RUNGS 14GA, 2-1/2x1-1/8 MIN OR EQ’
LADDER RUNG PLANK ‘TRACTION TREAD' BY McNICHOLS, 13GA, Ó-ROW BUTTON TOP OR APP'D EQ
LADDER RAILING AT TOP IS NOT DESIGNED AS A GUARD; AND
LADDER RUNGS SHALL BE NON-SLIP.
-HEIGHT OF LADDER MARINALLY EXCEEDS 5 M. A VARIANCE SHOULD BE OBTAINED FROM THE AHJ TO PERMIT ACCEPTANCE.
-SUPPLY AND INSTALL BILCO LADDER UP SAFETY POST MODEL LU-4 ALUMINUM OR APP’D EQ

LADDER ANCHORAGE
-SECURE LADDER TO SUITABLE BACKING WITH 2 – 1/2” DIA @ 4’-0” MAX O/C LAG SCREWS. EMBEDDED DEPTH INTO S-P-F #2 MIN LUMBER BACKING IS 3”.
-SECURE LADDER TO SUITABLE STEEL FRAMING BACKING WITH 2 – 1/2” DIA A325 BOLTS @ 4’-0” MAX O/C VERT. PROVIDE DIM LUMBER BLOCKING TO MINIMISE CRUSHING OF SIDING.
-SECURE LADDER TO SUITABLE MASONRY BACKING WITH 2 – 5/8” DIA @ 4’-0” MAX O/C THREADED ROD SECURED TO MASONRY WITH HILTI HY-HIT 270 ADHESIVE. EMBED LENGTH IS 6” MIN. PROVIDE HILTI SCREENS AS NECESSARY.
-SECURE LADDER TO SUITABLE CONCRETE BACKING WITH 2 – 1/2” DIA @ 4’-0” MAX O/C THREADED ROD SECURED TO CONCRETE WITH HILTI HIT-HY 200 ADHESIVE. EMBED LENGTH IS 4” MIN. MIN CONCRETE STRENGTH TO BE 20 MPA (3000 PSI).

If you are supporting the ladder at one edge of the checkered plate, it would be good to support that edge of the checkered plate with a small angle... maybe L2x2x1/4 (check the design). Determine if the ladder should be attached to the plate by welds or bolts. You can secure the checkered plate to the wood with lag screws (there are better attachments than lag screws; Simpson makes good fasteners).

There may be safety reasons that you may require a guard around the platform. You should look into this. Maybe even if a safety 'tie-off' is required?

Depends on the area of Ontario for seismic... not likely a problem, depending on use. Check with the Authority having Jurisdiction.

Good luck... (lots of edits).


-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[patstructural]

Thank you Dik.

 

[jayrod12]

Ho wide is that gap? Could it be plywood?

What's the final use? Just for service of the equipment?

do they require a guardrail around the platform or what's the fall protection scenario. As an engineer, you also need to ask the questions regarding items like this. It's not necessarily your responsibility to come up with all of the life safety requirements, but as a professional whose first priority is safety of public and users, you should be pointing out that working on an elevated platform like this should have fall protection in place.

I say that part because, if something were to happen to a worker that used your new ladder to stand on your newly designed plate, where they fell off of the service platform, you will be looked at as the main professional. In my experiences with things like this, especially when it's inside a manufacturing/production facility, their internal safety committee will usually need to weigh in. So what I've done is pointed out that we're creating an accessible platform that currently has no fall protection in place, and ask what the fall protection plan is for workers and whether the internal safety committee has had a chance to review and provide comment. Usually that results in proper attention being paid to the issue.