Design Reviews
Design Reviews
(OP)
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?
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?






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I am somewhat surprised that a one story addition of 3000 sf is even being reviewed from a structural standpoint.
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The shearwall aspect ratio is pretty key to the wall behavior in terms of limiting values in the code. The fact that the engineer failed basic load path derivation of diaphragm shears seems to me to be a red flag of the first order.
We just had a bunch of boy scouts here in the midwest get killed by nothing more than a chimney falling on them inside a small cabin. The cabin wasn't a huge building but the lack of structural integrity in the storm certainly was fatal.
While these particular mistakes were corrected, did this engineer also make other mistakes of similar nature? I'd request from the firm a review of the design by another engineer within the firm and a letter supporting the design.
Private practice does get scrutinized at times. As the owner, you have the right to expect competent designers...you are paying for them. Not error free designers, but competent ones that at least understand load paths.
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If the designer doesn't even know how to resolve the diaphragm shears, how the heck can he be expected to verify that existing shear walls can support additional lateral forces?
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All of the discussions that I have had have been with their senior structural. I haven't been given the opportunity to talk to the guy that actually did the calcs. What torqued me off was the cavalier attitude they had about these errors. It was as if the building would have been just fine without my review. Granted, they got lucky on the errors I did find. What scares me is, what else did they screw up that I didn't find?
Because we're the federal government, we have a higher responsibility to insure that taxpayer's money is being spent appropriately, otherwise it ends up on the evening news, so any unecessary costs are an issue. Although going from 5 welds per roof panel to 3 welds is not a huge cost impact, it's still a savings.
I'm a very detail-oriented person and expect contractors to comply with the codes and regulations that we use. I've also work at a regional building department and am very code conscious. It irks me when an engineer slaps a design down on paper and calls it good even if it has mistakes, albeit non-life threatening. That, to me, is irresponsible.
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Use your authority to "call a meeting". By that, I mean don't concentrate too much on your interpretation of the technical aspects of the problem. Have the vendor send his representatives to your office to explain why what he wants to do meets the code and will work. If the results are not satisfactory, call another meeting and go through it again.
Eventually, the vendor will literally get tired of attending all the meetings and may begin to listen to you a little more seriously.
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"... we have a higher responsibility to insure that taxpayer's money is being spent appropriately, ... so any unecessary costs are an issue. Although going from 5 welds per roof panel to 3 welds is not a huge cost impact, it's still a savings."
Yes it would almost pay for last hour you spent checking this one story building!
You need to realise that there are 2 ends to the cost equation and that it is not good economics to spend twice as long on a project only to save less than 10%.
But I agree that some firms take this too far and give the rest of us a bad name.
As long as clients continue to choose engineers based purely on price thse engineers will have their niche.
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I agree that is my job, however I don't want to be accused of splitting decimal points. For example, the engineer specified tension control bolts even though the connections were designed as snug tight. In his opinion, contractors have difficulties getting A325 bolts installed properly and the TC bolts will help the final product. Although I think this is overkill, I let this one go. I'm just trying to make sure I have a proper balance of what is really important versus professional difference of opinion.
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You might look at this from the other side, as well. When you design and detail something, and your customer reviews it and requests minor changes, it is often easier, simpler, and better to make those changes even if the customer is wrong than to convince the customer otherwise. This is not a comment on your two items above (not my field) but just to note that when you catch an error and their engineer says "okay", that doesn't always mean you were right and he was wrong.
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When we are in this situation we usually just make the changes.
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To me, this is not a case of a mistake that could be excused. This tells me that the engineer that designed this does not have a fundamental understanding of metal stud shear wall types and their limitations. In addition, we are paying for their senior structural to check this work, and he also missed it. I'm no expert here, I don't have advanced degrees in structural, but I was able to catch this right away just by reading through the calcs. I can understand a junior engineer making this kind of mistake but I can't excuse the senior for not catching it, and then trying to minimize the damage by making it sound like it was no big deal. Sure, they got lucky on this one, but if this is their attitude about this kind of thing, I would prefer not to work with them.
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These types of mistakes are not typically ignored in the private industry, especially the farther west in the country you go. In fact, I think in California, this type of crap would be cause for the state board to question his license.
You're only going to be called nitpicky if the deficiencies you find don't really matter and only slow the project down. With that said, if I were you, I would have ran a quick check of the shearwalls and included some verbage in your initial deficiency report...."hey, you've done something wrong, if you do it the correct way it's a close call. Please revise calcs and show that your design is valid." Usually, if the government reviewer comes off as a nice guy, nobody is going to have a problem with your comments.
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You are 100% correct in your approach to your task as reviewer. But I would not be so hasty as to condemn this consultant. In 40 years of practice, I have never had a government agency review my designs with your thoroughness, so don't know how I would react in the shoes of the designer. None of us like criticism.
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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
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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.
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...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.
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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.
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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.
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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.
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.
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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.
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Don Phillips
http://worthingtonengineering.com
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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.
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However, the engineer could be negligent, who knows. All to many are...
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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.
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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.
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I always thank a plan reviewer whenever he questions my design and especially when he is right.
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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.
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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.