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?

 

[civilperson]

("Too" versus "to"), you are finding errors for which you should be receiving thanks but the it did not make any difference in the material requirements or connections. As a reviewer for the client, your criteria controls but the errors listed are not life and safety critical, merely arithmetic corrections. You should have a stamp, "approved with revisions as noted".

 

[rb1957]

i'd accept your first point as valid, but the second (using a higher load than required) is a bit careless on the part of the engineer, but isn't a Real problem

 

[jike]

Although I don't like engineers to make any mistakes, we are all human (not superhuman as some may think) and it can and does happen. I would just hope that we would admit those mistakes and learn from them and hopefully they are on some small thing that doesn't affect the end product like perhaps in this case.

I am somewhat surprised that a one story addition of 3000 sf is even being reviewed from a structural standpoint.

 

[JAE]

I guess I'd agree that this isn't a huge building, but the errors you point out are not, in my opinion, "not life and safety critical". Arithmetic errors in structural engineering can be devatstating. Both mistakes reveal a complete lack of undererstanding.

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]red[/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.

 

[civilperson]

An addition to an existing building can probably share the shear wall bracing of the existing building to prevent collapse and rigid frame windows have ability to transfer some shear without racking. That is why I felt this was not life or safety critical. The collapse of the chimney on the Boy Scout camp was tragic, but I doubt that codes for wind could prevent this particular tornado damage.

 

[JAE]

The chimney example was an attempt to point out that even small additions can have huge ramifications if the design is flawed....not that codes could have prevented a collapse.

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?

 

[vmirat]

The perception that we have in the office is that A/E firms minimize effort to maximize profit, even if it costs the government a little more in construction. They're not going to give full attention to a $700,000 project so they give it to a junior engineer and don't even check his work.

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.

 

[SlideRuleEra]

vmirat - I have been an Owner's representative for most of a career. This will sound kind of "kooky" but I have found the following is one of the best ways to deal with vendors who don't take your input seriously:

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.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[csd72]

RE:

"... 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.

 

[lsmfse]

vmirat, It is my opinion that it is your duty to point out code violations. Isn't that why you are reviewing the plans?Maybe they are embarresed, too bad. Plan check agencies where we work require structural calcs for almost every structure, wether it is a 300 SF addition and especially a 3000 SF addition. Barns included!

 

[vmirat]

lsmfse,
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.

 

[cvg]

as a reviewer, your duty is to exercise the standard of care which a reasonable person (engineer) would do. No more, no less. You are in a quality assurance role which is to assure the government that the consultant's quality control procedures are working. It seems that you have determined that this particular consultant is perhaps having some issues with quality control. You may want to have a heart to heart with them and discuss ways of improving their QC program. However, the bottom line is that it is the consultant's butt on the line if there is a safety issue with a building he designed. It seems that so far they have not designed anything unsafe - but apparently over-conservative.

 

[JAE]

I think you have a poor consultant. Most firms I have worked for there is not this cavalier attitude towards clients.

 

[archeng59]

Did the engineer try to use the perforated shear wall concept? Still has to consider how the shear gets transferred around the windows, but that could explain using the total wall length.

 

[JStephen]

Once you know of stuff like this, you need to point it out.

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.

 

[csd72]

JStephen is 100% correct.

When we are in this situation we usually just make the changes.

 

[vmirat]

The engineer was not using the perforated shear wall method. Once I pointed out their mistake, they readily admitted that they used the wrong aspect ratio but tried to minimize their mistake by saying that it probably wouldn't have made any difference if the mistake wasn't caught. They agreed to go back and re-analyze using the perforated shear wall method. What was interesting is that they didn't mention anything about the reduction allowance in AISI Lateral for shear walls with aspect ratios between 2:1 and 4:1. If they had looked at it, they would have found that their design was just enough to meet the shear requirements. This tells me that they are not used to using this document for shear wall design, even though its use is required under IBC 2006.

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.

 

[Atomic25]

Hi there. I'm on the private side here, and work on government projects from time to time.

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.

 

[hokie66]

vmirat,

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.