Design Reviews 2

[vmirat]

I need a sanity check from you all that work in the private sector. I work for a federal government office as a structural engineer and am responsible to do reviews of designs that have been accomplished by outside architect/engineer firms. Recently, I reviewed a design that had several errors dealing with code requirements. I'll give you two examples so you can see my concerns.

This is a 3000 square foot addition to an existing building. It's 16 feet to top of parapet, 13 feet to roof deck, single story with flat roof (1/4" per foot slope), steel frame structure with shear walls, and metal deck diaphram. One side of the building has six windows with four feet between each window. Total length of building side is 54 feet. The engineer designed the shear wall as Type I without special consideration for load transfer around the windows. He added up the lengths of the wall segments between the windows and used that to determine the aspect ratio for the shear wall (i.e. 16/24). I explained to him that the aspect ratio must be calculated based on the dimensions of the wall segment between the windows, not the total shear area. Although he agreed with me, he said it was not a big deal and that he would revise the calcs by using the strength around the windows. The other mistake was in calculating the roof diaphram shear. He calculated the wind pressure on the wall (211 plf) but mistakenly used that as the unit shear load to figure out the attachment requirements for the deck (i.e. 1.5B22 deck with 5 puddle welds and two #10 tek screws). Instead of 211 plf shear, it is actually 112 plf. Again, he admitted his mistake but said that it wouldn't make any difference in the price of the building because the deck itself doesn't change, so it wasn't a big deal.

I've been accused of being too picky. They said that, in the private sector, building departments don't look that closely at designs, so they're not used to that level of scrutiny. I'm aware that regional building doesn't do the same level of review that I do, but code is code. Are these kinds of mistakes common and just ignored? Am I being to picky here?

 

[JrStructuralEng]

I think what every one is forgeting is that the client pays for the engineers time. On a smaller building, there is no cost savings to spend 4 extra hours to determine that you need 3 puddle welds instead of 5. Where is the economics?

A more common approach in the private sector, especially on smaller projects is to produce conservative calculations for none cost sensitive aspects of the project which actually save the client money in the end by reducing fees. Precise calculations are better suited for cost senstitive aspects of the building such as beams, columns, etc.

To give you another example, if you find out your beam only needs 3 bolts, but it takes you 2 hours of design time versus a conservative loading that takes you 10 minutes that lands 4 bolts. Cost savings to the client. **Thats what engineers get paid to do, we detemine the most economic amount of material to build the intended building safely**. Sometimes, the material economics is very small there is no point being super precise.

That said, I would laugh at someone telling me we need 3 puddle welds not 5 on a building of this size. The bigger problems is your contractor will probably put on 10 half-@ss welds and then you will have to figure out the approximate capicity of thier bad construction. hehe

 

[vmirat]

JrStructuralEng,
I'm not asking for more detail, just for the design to be done right. The engineer made a mistake. Whether it was due to inexperience or carelessness will probably never be known, but it was his mistake and it would have cost the federal government more money in construction (every penny counts).

By the way, this is a pre-negotiated lump sum contract with the engineering firm, so their mistake costs THEM money by having to redo the calcs and resubmit them for approval, so it's to their benefit to get it right the first time.

As I said previously, this is a federal government project and the costs are scrutinized very closely. The type of money being spent is limited by public law to $750,000. We are VERY close to that limit with this project, so we can't afford conservative engineering, regardless of whether it costs us more in design (different kind of money) or not.

This is not a case of conservative design. The engineer made several gross errors in his calculations but tried to make it sound like it was no big deal. Fortunately, the mistakes that I found erred on the conservative side, but what else did he screw up that may be under-designed?

The guy had to do the calcs (design analysis was required by contract), so why didn't he do it right the first time? Now, he has cost the government time in additional reviews and delays in getting the project started.

As a side note, my method of design review is to do a cursory check of the basics (live loads, code requirements, etc.). If those things look good, then I tend to pass over the details. I happened to catch his mistake on the shear wall aspect ratio just because my eye caught it. Once I find something like this, that's when I go into detail. I don't have the time to check every calculation. That's why we paid them for a senior structural's time.

 

[JrStructuralEng]

I agree with many of your comments regarding the design process...but you should know that the designer has a "goverment" charge added in to his fixed fee. You are paying for this type of time consumption whether it is on this project or the next is the question.

...but I think you may have a glorified view of construction process. Every penny on a 3000sqft building does NOT count. I can see you havn't done estimating before. Unless your contractor has nothing better to do than count puddle welds I can guarentee he does not even take one look at this when he bids the job. The job is only worth what someone is willing to pay for it. And in the goverments case, their pockets are very deep.

I am not trying to be ignorant, but try to picture this from both sides of the equation. Even if he has already bid the work. The more you chizzle, the more the contractor will look for extra's to charge you.

 

[csd72]

re:"it would have cost the federal government more money in construction (every penny counts)."

Have you counted how many pennys it has cost the government while you have been blogging on this site? I noticed that your last post was very well thought out and spell checked and posted at a time that is during work hours everywhere in the US.

Not meaning to get on your back about it, but you have to put things into perspective. The builder does not build from the calculations.

Cost is mostly influenced by the complexity of the design rather than the sum of its parts, if you make a lean but confusing design then it will actually end up costing more money.

 

[tngolfer]

I think what vmirat is saying is, something as simple as opening Vulcraft's book, going to the table of deck gauge and puddle weld size and comparing your applied loads (uplift from wind, shear from lateral, etc.) to the allowable loads in the table costs the engineer about 5 minutes. If the design engineer is not going to look at that to save 4 minutes, what else is he/she not going to look at?

I also agree with the concern that the design engineer didn't do the shear wall proceedure correctly and mess up a number, he/she just didn't do the proceedure at all.

What I don't necessarily agree with is saying that fewer welds are allowable. They may have a reason for bumping it up to five but in their calcs if they don't say, "3 works, but use 5 because..." it would appear that they may not know what to check the welds against.

 

[JrStructuralEng]

I agree with cmd72 100%, no wait... 110%. Complexity of design is the key factor here. Then add in a little complexity for dealing with teh government and you have a pricey project.

 

[JAE]

That said, I would laugh at someone telling me we need 3 puddle welds not 5 on a building of this size.

JrStructuralEng - I think your points are valid enough as they go....that fine tuning the design to be more "economical" sometimes takes much more engineering effort than it is ultimately worth.

But the real point here, in my view, is not that vmirat saved 2 puddle welds (3 vs. 5) but that the review discovered some errors that tended to reveal that the design engineer didn't know what the heck they were doing....not that they were trying to be economical in their design time....

There's big difference between these two scenarios:

A) Quickly designing a beam connection (your example) for 4 bolts and knowing you are conservative (vs. 3 bolts)

B) Quickly designing a beam connection for 4 bolts when you don't have a clue whether 3, 4, or 5 bolts are required.

[red]The fact that the design engineer's clueless mistakes ended up being conservative doesn't give vmirat "warm fuzzies" that the rest of the bulding is safe.[/red]

 

[vmirat]

There is another aspect of government contracts that I would like to explain. This particular project is contracted through our SABER program. This is an Indefinite Delivery/Indefinite Quantity type contract where the prices for labor and materials are pre-negotiated using the R.S. Means Facilities book. Construction contractors are required to provide the government a detailed line item proposal using a program call e-4clicks. At the same time, the government engineers are required to develop an independant government estimate using the same software which can be compared with the contractors proposal. As the government's technical representative, I must account for every line item in the contractor's proposal. If there is a discrepancy, I must resolve it. This results in either the contractor revising their estimate or the government revising theirs until a common figure is negotiated. The final award is lump sum.

Sometimes there are things we just let the contractor have if it's a minor difference, say 5 welds versus 3 on a 3000 square foot building. It depends on the job. However, I think you all can see why I must be "picky."

Everyone thinks Uncle Sam has deep pockets. Well, where I work, we ain't gittin all that money ya'll think we is. You would be very surprised at how many things we need to fix and how little money we get to do it. So, we are very protective of what we get to spend.

 

[DonPhillips]

The Feds', like any very large business, has 2 very large expenses - human resources and physical facilities. So they may bring in trillions - I mean - spend trillions per year, this does not mean they have deep pockets - especially when someone decides what the budget is and you have to figure how to deliver it.

Don Phillips

http://worthingtonengineering.com

 

[B16A2]

Virmat,
Speaking as an engineer in the private sector. Thank you for doing an honest review. I don't care how small the project is. Keep it up.

The engineer sounds negligent. Everyone makes honest mistakes, but anyone who schluffs off basic load path calcs like that should not be practicing structural engineering. They should be concerned and apologetic, or even embarrassed.

As JAE said, there is a huge difference in designing for economy and being clueless and using "it's conservative" as an excuse.

 

[JrStructuralEng]

I agree with you JAE, my beef was in the 'economy' portion on his post. There will be no ecomony of savings in reducing puddle welds.

However, the engineer could be negligent, who knows. All to many are...

 

[pba]

It is entirely possible that the Senior Engineer's relaxed attitude was a front in order to help protect his companies position.

It sounds to me as if Virmat is taking the failures in this calculation rather too personally. A detached and professional attitude is needed.

Basic load path errors are a worry and should be fixed. They are often made by junior engineers - as may be the case here. Such errors should be picked up by internal checking, but in this instance at least, have not. No checking procedure is 100% effective.

The presence of this error alone indicates that further review of the design is warranted. It is for the various parties to determine how this review is to be conducted.

If there is genuinely no faith in the designers, it would be prudent to not enter into contract. If there is faith, then it should be a requirement for the designers to correct any substantial errors.

Conservative design, caused by the incorrect use of a wind value could well be made acceptible without recalculation by simple annotation of the original calculation. This should be left as a choice for the designer.

 

[csd72]

vmirat,

I agree with the last 2 posts, I was referrring more to your comments on economy rather than the major load path issues.

I have checked quite a number of jobs including those done by very good engineer with 40 years experience, and EVERY one had mistakes. The more experienced the engineer the smaller the mistakes, but there were still mistakes.

The secret is to learn which mistakes are really an issue and which are not. The gripe that I have with most people in your position is that they pick up every mistake and require it to be rectified, even if it is of no significant consequence.

I apologize if my posts above sounded confrontational and overly critical, that was not my intention.

 

[FSS]

Count me on JAE's side, as I agree with his posts.

I always thank a plan reviewer whenever he questions my design and especially when he is right.

 

[csd72]

FSS,

Yes I agree with you that it is a good thing when a checker finds something of importance - this is their job.

But I have a job at the moment where I have had to revise half the calculations due to pedantics even though all of the members shown are 100% adequate.

When an experienced engineer designs a job, they will not put calculations to every single item for every single case as they will know that certain items are just not critical. When you get an inexperienced checking engineer ( not referring to vmirat here) then you are forced to do every single calculation. This is a common problem in the UK where all jobs are(or at least were) checking by the permitting authority.

For this reason, I do not check calculations, only drawings. I will only look at calculations if I do not understand their design assumptions/philosophy. I also believe that checking jobs based on calculations is an inherently dangerous method, where the checking engineer may follow the same logical error as the design engineer.

Anyway I have bored you enough with my rant for now.

vmirat, as I said before, nothing personal - am just a bit annoyed at one of your counterparts in another federal department.

 

[vmirat]

csd72,

I can appreciate your frustration. That's why I posted this thread....to make sure I wasn't being too picky. I've often asked myself why I'm spending so much time review these designs. My counterparts at the regional building department don't go into this level of review, so why should I? I suppose that position could be taken on many of the projects we do. However, there are certain projects that we have which are related to national security. Failure in these facilities would have far reaching affects, so we need to be more critical of those designs.

As I said in a previous post, I usually do a cursory check of the calcs to insure code compliance (keep in mind that I am the "regional building department" here since it involves a federal facility). I actually start my reviews with the drawings before I get to the specifications and design analysis, if for any other reason than to understand the design they have. There are things that will cause flags to go up in my mind (such as a lot of windows in a shear wall) which will cause me to look further into that area of the design. I guess you could say I approach review like an onion. I look at the whole onion first, then start peeling back the layers. If I find a bad spot, I'll start to peel some more to see how deep it goes. For example, I looked at the foundation design and didn't see anything of concern, so I didn't even look through their calcs for foundations.

Design review is a lot like the actual design process. An experienced engineer can check a design quickly and without a lot of checking of calcs, which saves time and money. I've always tried to balance practicality with accuracy when I do reviews. However, there are times when I must hold a designer to task for errors that appear to be a result of carelessness. And I won't stand by and let a design go if mistakes cost me more money in construction. That's like a double-wammy. I didn't get what I paid for in design and paid more in construction for it.

The more complicated they make the codes (I've already posted a thread on that one!), the more important it is to check the work, whether it be in-house or by a review agency like myself. In this case, the contractor's own QC system (i.e. the senior structural) missed all of this stuff.

As a professional, I always try to self-evaluate what I am doing. That's why I posted this question.

By the way, I wanted to address a comment someone else had made about the time I've spent (or wasted) posting this question. I visit Eng-Tips every day to see what things I can learn, and I've learned quite a bit because of it. Where I'm from, we don't have CEU requirements for registration, so Eng-Tips is a great way for me to stay sharp on things. I'm really grateful for this web site and I appreciate everyone's comments.