Corroding beam @ stair
Corroding beam @ stair
(OP)
I wanted to pick smarter brains here for a problem.
Existing stair, built nearly 40 years ago. See attached sketch for a layout. There are four stringers, each TS6x4. One of the stringer has significant rust while another one has some rust on it.
Repair: I figured that adding new plates to the existing HSS is not going to do anything because of the amount of corrosion. So I want to put in new beams to support the stair as shown.
My question is in regards to the existing steel that's already corroded. Would you recommend it to be welded with plates and painted to be left in place, or would you remove the entire portion of the corroded beam and replace it with new?
Also, because of the corrosion issues, I am going to have the new steel galvanized and then painted. Considering that this is an interior application, is that overkill?
Thank you,
Existing stair, built nearly 40 years ago. See attached sketch for a layout. There are four stringers, each TS6x4. One of the stringer has significant rust while another one has some rust on it.
Repair: I figured that adding new plates to the existing HSS is not going to do anything because of the amount of corrosion. So I want to put in new beams to support the stair as shown.
My question is in regards to the existing steel that's already corroded. Would you recommend it to be welded with plates and painted to be left in place, or would you remove the entire portion of the corroded beam and replace it with new?
Also, because of the corrosion issues, I am going to have the new steel galvanized and then painted. Considering that this is an interior application, is that overkill?
Thank you,






RE: Corroding beam @ stair
RE: Corroding beam @ stair
RE: Corroding beam @ stair
RE: Corroding beam @ stair
RE: Corroding beam @ stair
I agree with ztenguy that a good first step is sandblasting. This will give you a better idea of the extent of the rusting.
BA
RE: Corroding beam @ stair
I couldn't figure out why the rust was so localized and at that particular location. To me it appears that there is water infiltration from the basement wall. But why is rust more prominent away from the wall rather then right at the wall is a mystery to me. My guess is that since the water ends up sitting more often in the center of the beam (since the beam is definetly deflecting near mid span), their has been more prolonged exposure to water then the ends.
RE: Corroding beam @ stair
BA
RE: Corroding beam @ stair
In effect, you would have a system that looks like the attached idealized sketch:
RE: Corroding beam @ stair
I am reluctant to get rid of the existing tubes because they are embedded in conc. I want to enclosed the damaged portions with welded and painted plates and leave the existing in place.
RE: Corroding beam @ stair
Also, this is REAL picky on my part, but a bent plate should be called out with the thickness listed first...i.e.
BENT PL 1/4 x 8 x 2 x 0'-6" @ 8" o.c.
RE: Corroding beam @ stair
Thanks for pointing out the correct designation but can I have a picky question. Since this is a bent plate and not an angle, am I not supposed to show the " (inch) symbol with every dim? I thought with angle you don't have to show " but with bent plate you do. Am I wrong?
RE: Corroding beam @ stair
It would be desirable to leave the existing steel intact if possible, but the source of water and the extent of rust need to be known before moving forward with a solution.
BA
RE: Corroding beam @ stair
I always use ft and in. symbols on the length only. I may be wrong from a "picky AISC" perspective though.
I would second BA's recommendation to solve the water source as part of your effort. Also, I would worry about the slab itself. Do you know if the landing/stair slab system is deteriorated as well?
RE: Corroding beam @ stair
There are no visual signs of any damage to the slab itself but I am not sure how to verify that.
As far as water source is concerned, like I said before this has to be coming in from the side bearing within concrete. The top of landing and actually bottom of existing HSSs is above grade (see attached pic taken from outside). I can't think of any other water source then the what is creeping up the foundation/basement wall and finding its way into the steel.
RE: Corroding beam @ stair
Also, I am not surprised to see the rust in the tube members - there is no ventilation... For the new galvanized hat sections, I would encourage you to install some vent/drain holes as you will be sealing up the members again if they are not installed, leaving the possibility of future rust. Galvanize the hat sections after the holes are drilled.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Corroding beam @ stair
I was definitely going to recommend galvanizing of new steel. One of the reasons I am keeping the new and old steel separate is because existing is not galvanized and as far as I know if galv and non-galv steel are in contact, the galv will try to galvanize the non-galv part. So I may have a problem at the moment connection of the new and old steel i.e welding galvanized plates between a new galv section and existing non-galv section but I don't see a way around it.
As far as vent are concerned, I was planning to place two small holes in the horizontal leg of the bent plate (6" long). For the new HSS I don't want to leave the ends open so I'll use cap plates but would it be advisable to have some small vent holes at the bottom side of the HSS? Do I just put on the drawings that I need vents for the steel guy to do his thing or do I need to spell out size and spacing?
RE: Corroding beam @ stair
JAE.... sorry about the mixup on the sketch attribution, even though it wasn't my doing. Probably happened out of force-of-habit, since most of BA's post usually include the phrase, 'please provide a sketch.'
RE: Corroding beam @ stair
RE: Corroding beam @ stair
BA
RE: Corroding beam @ stair
RE: Corroding beam @ stair
BA
RE: Corroding beam @ stair
RE: Corroding beam @ stair
You are planning to enclose the existing hollow section within new steel framing according to the sketch in your first post. If you drain the old HSS, you will be retaining water on top of the new HSS which you cannot drain. I wonder if that is wise.
BA
RE: Corroding beam @ stair
Looking at his first post, those bent plates are not continuous. Not sure if that is a good idea or not, just saying... I don't like the proposed scheme of leaving all that corroded steel in place.
RE: Corroding beam @ stair
I missed the fact that the bent plates are not continuous. That makes me wonder how the new 6x4 HSS on the flat can adequately replace the corroded 6x4 HSS members.
I don't like leaving the corroded steel in place either. I still believe that more investigation is needed to determine the extent and source of the corrosion.
My preference would be to eliminate the source of water and to replace the existing beams, field welding to the sloping portion as required. I don't think galvanizing the replacement material is appropriate in that case.
BA
RE: Corroding beam @ stair
RE: Corroding beam @ stair
An opening in that location would preserve the shear strength of the member. The moment is negligible near the reaction, so the loss in moment capacity should not be critical.
BA
RE: Corroding beam @ stair