I Hate Pricing Episode #476 - Determining Wind Loads on a Replacement Membrane for a Domed Stadium 2

[KootK]

So I have a client with an interesting project. They're going to replace the roofing on an entire, domed stadium. Like an NHL stadium, non-retractable. I'm going to help by working out the wind loads on the new membrane. I'd like recommendations on fee considering:

- Even done with great care, I could see being done with this in 12 HRS or less. So... $1,500?

- If the new roofing flies off during a Hurricane, I could see getting sued for ONE. BILLION. DOLLARS! So... $4,500?

I'm looking into the construction budget and the scale of my client's fee. We'll see how that goes. I like these guys so I certainly don't want to be perceived as gouging. But, then, I also don't want to be foolish from a business perspective as is, unfortunately, often the case.

What would you do?

 

[jayrod12]

Geez,

For that, I think your $1500 is almost steep. as long as the room if fairly regular shaped, i.e. a case defined by the code without significant interpretation.

 

[TehMightyEngineer]

That changes my advice somewhat:

I presume that there are different membrane grades/adhesives/etc. such that there is value in having refined loads? Or is this something where you simply need to find the highest wind force and the waterproofing membrane is typical for the whole roof?

I may be completely off, but I'd price it based on the estimated value your service adds to the client. Perhaps inquire with the roofing supplier (or estimate it yourself) about how much cost you can save them by going from X mm thickness to Y mm thickness or X adhesive to Y adhesive or whatever variables you can change. Estimate how much money a refined analysis costs you. Maybe not wind tunnels, but things like working out different C&C loads for major areas/elevations of the stadium, or subbing out some computer modeling of the structure to get more refined results than typical C&C design, or even a wind tunnel analysis at the extreme.

Even with a symmetrical structure there are predominant wind directions. You could investigate probabilities and determine that some areas of the structure can justify a lower safety factor and maintain the same targeted risk level.

From there, calculate roughly the potential savings a refined analysis can save the client. If you figure that you can save them $100,000 on material you should take 5-10% of those savings and everyone wins.

Unless there's no way to optimize the roofing material, I'd suspect your client wants to spend money on you so that you can add value to their roofing work and turn around and save them even more money. Client spends money to make money and you make money in a fair, friendly way to keep your client happy. If you just give them $1500 to work out the maximum C&C load but another engineering firm says for $10,000 they can give them refined loads and save them $100,000 then you're actually doing them a disservice by not trying to add value to their work.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL, HI)

 

[canwesteng]

Seems more likely to me the client has a number for uplift they're expecting, to match what they can achieve with their system, and just need someone to sign off on the load. If that's the case I'm with jayrod, fees seems a little high but rate seems a little low. Caveat is that if wind testing is required and you need to manage that you probably need a higher fee. I'd be inclined to get some not to exceed number from the roofing guys and see how much number crunching it takes to justify it.

 

[KootK]

For that, I think your $1500 is almost steep. as long as the room if fairly regular shaped, i.e. a case defined by the code without significant interpretation.

Well... it's a stadium so it may well be a bit different. I ended up going $2500. That, because:

1) I still work out prices considering liability at times. Frankly, that relationship exists, for me, because I say it does. If the roofing flies off of an NHL stadium and I get sued out of existence, I'd not be looking back too fondly on a $350 fee.

2) This is something that I want to do carefully and double check a few times. I'll probably run it through some non-Canadian codes and take a careful look at how uplift on the membrane may or may not be different from uplift on the roof plenum as a whole (what we usually look at).

I presume that there are different membrane grades/adhesives/etc. such that there is value in having refined loads? Or is this something where you simply need to find the highest wind force and the waterproofing membrane is typical for the whole roof?

Dunno. Priced for the former rather than the latter.

Seems more likely to me the client has a number for uplift they're expecting, to match what they can achieve with their system

Subsequent discussion with the client has proven this to be correct.

 

[KootK]

Fine... I backed of to $1500. If I get killed on this, however, heads is gonna roll.

 

[TehMightyEngineer]

Subsequent discussion with the client has proven this to be correct.

If that's the case then I'd say you're on the right track with $2500 Edit: $1,500?

I can see why you struggled with this one; the responses of the hive mind are all over the place.

Regardless of your price I agree with some jobs pricing in some of the liability. If you design a simple detail but the liability involved would instantly bankrupt you it makes no sense to be bottom dollar. Risk involved has to be priced in at some point.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL, HI)

 

[KootK]

I can see why you struggled with this one; the responses of the hive mind are all over the place.

Yeah, really did not help myself with the membrane confusion. It just goes do show: even pasty, middle aged, non-ESL guys with astounding vocabularies can bocth the whole engineering communication thing. Long live the sketch I guess. I'm usually pretty sketch forward but I truly thought there'd be no value in it here.

 

[WinelandV]

Come on KootK, they don't still have debtor's prisons is Canada (I hope).

You just get to move back in with your parents or your wife's parents.

 

[WARose]

Somebody's probably already mentioned this, but I'd be sure you gave yourself plenty of admin time with this.(I.e. reading reports, meetings with them, etc.)

I've done this before and it's not like evaluating a geotech's report....there's a lot of "ok so what do I use here? What is this?" and so on.

 

[Agent666]

As an aside, if there is any doubt about risk, I find it funny how many responses have been along the line of dealing with or accepting the risk = simply getting paid more dollars to do the job. This isn't actually dealing with the apparent risk at all.

If the risk is an issue, don't do the job or mitigate the risk, transfer the risk or some other strategy until it is acceptable to you, if the client doesn't accept the risk mitigation then don't do the job.

Having $1.5k more in your pocket doesn't really help if that risk eventuates. Just saying $1.5k -$1M = approx -$1M, vs $3k - $1M = approx -$1M, spend it well I guess.

 

[KootK]

I find it funny how many responses have been along the line of dealing with or accepting the risk = simply getting paid more dollars to do the job. This isn't actually dealing with the apparent risk at all.

I disagree strongly. Thanks to the Scottish Widow's fund, there's an entire field of study dedicated to assigning dollars to risk. That isn't the only way to mitigate risk but it sure as hell is one way.

If the risk is an issue, don't do the job or mitigate the risk, transfer the risk or some other strategy until it is acceptable to you, if the client doesn't accept the risk mitigation then don't do the job.

I'm impressed that things are so clear cut for you. Care to:

1) show me any meaningful engineering assignment where risk isn't an issue and/or;

2) share some strategies that I might use here to mitigate or transfer risk other than the obvious, monetary/QC routes?

 

[JAE]

You look good in a mask.

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[JAE]

Check out Eng-Tips Forum's Policies here:
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[KootK]

It's a pretty good likeness really. Beady eyes, chicken legs, a touch of rosacea. Take the whiteness of the teeth down a shade or seven and we could be twins.

 

[TLHS]

On the cheeky side, I'm pretty sure dome uplifts are smaller than conventional peaked roofs. Could you spend an hour proving that to yourself and then, since the Canadian code doesn't have figures for domes, calculate a conservative uplift force using the available figures and use that? Built in conservatism that gives you likely still conventionally constructable numbers with a 'best effort at using code' justification!

 

[KootK]

On the cheeky side, I'm pretty sure dome uplifts are smaller than conventional peaked roofs.

I had the same thought. In local terms, I'd bet money that there's less net uplift on the membrane of this dome than there is on the overhang of my hip roofed house.

Could you spend an hour proving that to yourself and then, since the Canadian code doesn't have figures for domes, calculate a conservative uplift force using the available figures and use that? Built in conservatism that gives you likely still conventionally constructable numbers with a 'best effort at using code' justification!

I could. In addition, I'd planned to run this thing through some of the international codes that tackle domes more explicitly. I offered up $1,500 but my client went ahead and put me down for $2,500 anyhow. They're great. Anyhow, there's plenty of fee room for me to do an excellent, peer reviewed job of this.

 

[CANPRO]

I'm not sure your typical roof uplift calculation applies to the membrane. Roof uplift is driven by a pressure differential between interior and exterior - in this case the "interior" is the space between the membrane and whatever comes next in the roof assembly.

I've been reading your replies for years now KootK, good to put a face to the name...

 

[Ron247]

I know nothing about this topic. But... this is the longest thread I have ever seen. Congrats Rapunzel.

Oops, I spoke too soon, just saw one that is longer so I had to edit this message.

Just joking, but these are the threads I pay the most attention to. I am a 1-man company, so the threads with a lot of viewpoints and back and forth thought are very valuable to me. I have no one in the office to bounce thought or ideas off of.

 

[KootK]

I'm not sure your typical roof uplift calculation applies to the membrane.

Me neither and that will be a real part of my learning process. If anybody has a definitive answer on how one calculates membrane uplift, I would welcome input on that.

Roof uplift is driven by a pressure differential between interior and exterior - in this case the "interior" is the space between the membrane and whatever comes next in the roof assembly.

While I've not sorted this out for myself yet, I'm not so sure that I agree with you on this. Unless one can prevent interior air pressure from making it's way to the membrane, I would tend to think that it would be something similar to the differential between interior and exterior. After all, the membrane usually is the air barrier "thing", right? Perhaps one needs to modify the usual procedure to account for lag in equalization between the interior volume and the underside of the membrane?

I've been reading your replies for years now KootK, good to put a face to the name...

It will be most expeditious for you to think of me as the temporally unlikely genetic love child of Fazlur Khan and Brad Pitt.

 

[KootK]

But... this is the longest thread I have ever seen. Congrats Rapunzel.

Pfft... noob. Check this one out: Nutso

I have no one in the office to bounce thought or ideas off of.

#MeToo +/-. I've actually been working hard to build up a network of folks in similar situations to whom I can bounce businessy stuff off of. Eng-Tips is useful for that but not perfectly so. Mixed with the solid business advice, you also get a lot of responses that, to me, look like what people think their "perfect selves" would do rather than what they would actually do in practice. If you'd be interested in another commiserator, a little riddle solving will get you in touch with me: KootK