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Residential Concrete Deck on Steel Beams 6

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STrctPono

Structural
Jan 9, 2020
706
The longer you look, the worse it gets....

I'm helping a colleague as they are in escrow to buy this house. I'm headed out tomorrow morning to take a look at it in person.

This portion of the outdoor lanai is a concrete topped metal decking (however, I don't think that is a metal deck and looks more like corrugated roof panels??)

I am certainly going to have a punch-list of things to do, based on priority, however the one thing I keep coming back to is the metal deck itself. It is going to continue to get worse and I have no idea how much concrete topping is poured above, therefore I have no idea if the metal deck is necessary or if it is more of a stay-in-place formwork. Given the quality of construction, I would think this Contractor didn't pour an ounce more of concrete than was absolutely necessary... What do you think?

Either way, I'm thinking that to stop the progressive corrosion of the underside of the metal deck it should be abrasive blasted and then repainted. Additionally, I am thinking that the top of the concrete should be sealed with an epoxy flood coat or something similar to slow moisture infiltration. Any thoughts?

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I’m all for “friends hat” when called for, but vouching for this crazy thing is quite a stretch.
 
Legally, your friend can indeed toss you under the bus if you say all is well. In that respect, it depends on how much you trust your friend.

That said, I wouldn't be saying thst all is well. I would be saying:

1) this is what I can prove.
2) this is what I can't prove.
3) this is my my gut feel for performance and risk in this situation.

Basically the same engineering opinion that I'd offer a paying client.
 
That's my point KootK. The OP is saying he'd recommend a complete rebuild to a client but not his friend. I don't see how you can justify such a drastic difference in recommendation. I can see turning down this project due to liability with a paying client but I also wouldn't provide recommendations for free to a friend on something like this.

I've always said "families get along until there is money involved". I've seen it time and again that siblings get along great until it comes time to divy up their parent's wealth. It'd be a pretty rare friend that wouldn't throw you under the bus if sh*t hit the fan.

I also don't like the view that a "deal" could fall through if we are too hard on the condition of this thing.
 
Ah... okay, I understand your perspective now Rabbit.
 
Another thought to add to your collection:

The slab thickness cannot be determined from your photos, but the photo from the top side shows that the slab is jointed. I would conclude then that the concrete is not structural, and rather that the corrugated steel deck carried the load. Since the deck essentially no longer exists, the slab could collapse locally without much additional loading. The shadows at a couple of the joints indicate there has already been some differential deflection.
 
The first line the Op says it all IMHO.

KootK is right up to a point - it's still standing (somehow) and shows no clear signs of distress as far as we can see from the limited amount of information. Please tell me it's not a cantilever at the edge....

However, the issue for me is that you have no control at all over what the new owners will ever use it for.

Get a birthday party out there in the sun and bit of dancing and down she goes. Quite steep drop by the look of it.

Is some of that concrete under the wooden decking? Did they build the wooden decking to hide the cracks in the concrete?
I would be telling your friends that it is essentially structurally unsound as it sits now and you wouldn't feel comfortable with any more than 4-5 people on it and collapse might be very sudden. To fix it to get it semi decent might be ~$20,000?? $40,000? but then they will have a proper deck. If that's a deal breaker then so be it - their money and health

The only thing that tells you the deck might be a bit stronger than it looks is that the "formwork" which has all the appearance of corrugated roof sheets, hasn't collapsed and the concrete may well have some re-bar in it. but you need to destroy part of the patio to find out.

Fix the missing column, double up on the timber beams and turn them the other way around and limit the numbers on the deck to no more than 15.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
 
Ingenuity, not a chance that this was permitted!
KootK, Thanks for all your input.
Hokie66, The joints appear to be steel screed rails that they left embedded in the concrete. They run parallel with the deck flutes.
LittleInch, there is a cantilever on the ends. Surprisingly, the corrosion of the steel beams can be considered mild to medium. I am essentially telling them something similar to what you suggested but a bit more conservative on the condition as it stands. I think the cost of the critical fixes would be lower than $20,000. My estimate for a brand new deck is $75,000.

I did get a chance to inspect it for myself. It really is a monstrosity. The craftmanship is very poor and there was an improper use of materials right from the get-go. There is also very poor drainage in some areas which is exacerbating some issues. With all that being said, I have come up with a list of critical fixes that IMO actually salvage this lanai for a bit more time with annual inspection. My gut feeling is that this could still be used for approx. another 10 years until the section loss in the steel beams gets too excessive. Current major section loss of steel beams and columns is limited to only 3 select locations. Wood joists need to be replaced, redetailed, and closer spaced to account for an assumption of plain unreinforced concrete deck. Concrete deck varies from 3.5" to 5.5" to bottom of flute. Several column bases need to be fixed.

I do appreciate the insight from everyone. I understand that it seems that I am taking a path that not many agree with but based on my observations I do not feel as if this lanai is in danger of imminent collapse. Although tempting to take the easy route and just condemn it outright that does not feel like I will be doing them a service. I am certainly taking care to document my findings and write it in such a way that helps protect myself from the brunt of the initial liability. Thanks to all!

 
anymore when a friend/family or a friend of a friend asks for engineering help, I always refer them to a competent engineer in town if possible.
 
LittleInch said:
I would note very heavily that they shouldn't have a party on it....

Exactly! I would also make sure they don't put planters with soil, water, and plants (110 pcf) -- nothing more than a lightweight table and four metal chairs. You'd be amazed at what owners will put on a deck.

STrctPono said:
salvage this lanai for a bit more time with annual inspection

What is the cost for annual inspections? Or will you do the annual inspections, casually, while visiting? What happens if you are no longer visiting this friend? At what point do you say, "Put up CAUTION tape and Do Not Enter signs and stop using this deck immediately"? What if your friend refuses to stop using it? For that matter, do you have to sign anything saying that the deck is in useable condition right now? I would not put my name on anything related to this deck.

STrctPono said:
Concrete deck varies from 3.5" to 5.5" to bottom of flute

Do you mean that there is at least a 3.5" slab everywhere, but it goes deeper, to 5.5" at the bottom of the flute? Is there any evidence of reinforcing?

STrctPono said:
Current major section loss of steel beams and columns is limited to only 3 select locations

What happens when one of those becomes a point of failure? What will the progression be?

I would stay far, far away from certifying the viability of this structure, and I would also refuse to step foot on it.
 
@STrctPono:

Your attempt to wear your "friend hat" has inspired me to post about my recent attempt to wear my "neighbor hat": Link.

The nature of this space is that we tend to hear conservative viewpoints more loudly than others (often that's me). And, for the most part, I think that's healthy. At the same time, I feel that it's useful to hear from other risk-dummies from time to time so that we have an accurate perception of what's actually taking place out in our profession. So count me as a data point in that respect.

Butchering Einstein: Do not worry about your quandries in professional risk taking. I can assure you that mine are greater.
 
This deck does not look too big. How could it possibly cost 75k to replace?
I'm with the majority here - tear it down before someone gets hurt.
 
XR250, The deck is 750 sq. ft. Approx. $100 per sq ft construction cost for that type of deck. That doesn't even include demolition of the existing deck.

Everything is expensive where I live. Same reason why I just paid $5200 for a KX65 when MSRP is $3700.

Ingenuity, $1.9M. Nice cul-de-sac up in Nuuanu.

KootK, I have been enjoying following your post about your charity work. That was a ton of effort on your part to stick with that thread and address everyone's comments.
 
An owner who pays $1.9 million for a house should be happy to pay $75 thousand for a deck without structural defects.
 
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