3D modal Analysis calculation package

[Prestressed Guy]

When performing a 3D modal Analysis with one of the many software packages, I have had different responses from plan reviews within the same building departments. Most of the time my projects are approved without comment but other times….

I currently have a single family residence that is to be built with concrete bearing walls (ICF) and SJI floor joists with composite concrete floor slabs. The structure is on a view site and is all window towards the view. Because of this it is a torsional irregular type 1a building. Even so, it is extremely stiff with very little stress in the walls. The plans reviewer has requested additional information 4 times. It seems that no matter what I send it doesn’t seem to answer her questions. I am temped to just do a full output dump to a PDF file and send it to her but that would run to approximately 20,000 pages. This building is your proverbial concrete sh__-house. It seams that the reviewer works mostly on wood stick framed houses and is trying to perform a full hand check on my calculations. She is asking for simplistic answers to complex question.

So what do you normally submit in the way of a calculation package?

 

[DWHA]

I normally submit enough information for the reviewer to re-create the model I had. That way they can either do the analysis by hand or in a computer model of their choice. This helps to compare apples to apples.

 

[rb1957]

oh, i hear the pain in "She is asking for simplistic answers to complex question." ... been through that hell myself.

i won't dump a ton of paper on the desk of someone who you need to approve your work. i'd sit down with the reviewer and try to understand their difficulty ... if they're out of their depth (unfamiliar with concrete structures), throw them a life preserver ! only if you're going nowhere would i play the "let's ask your supervisor" card.

 

[JoshPlumSE]

Some plan check engineers may just want to review your model. If you just give her your model then she may satisfied....

Then again, she may take a month to review your structure while she tries to learn the modeling concepts and analysis concepts that she is struggling with. During which she could nit-pick every tiny modeling decision you have made.

 

[graybeach]

I agree that you should sit down with her and try to understand her concerns. She may well have a point. I am usually on the other side of this problem. As a reviewer I want to see that the analysis addresses all likely scenarios and that entire load path is addressed. If the drawings show some weird bracket with 10 kips eccentric load on it, I want to see that every part was looked at. Sometimes I have to take out a pencil and paper myself and check these things. All too often, I find that something will not work.

 

[Prestressed Guy]

Rb1957 is close to the mark. The plans are going through the residential section of the building department. They usually review plans conforming to the IRC with lateral analysis usually performed by a civil engineer. This analysis is quite often rather suspect with a vast array of skill in the engineers performing the work.

In this case the building is designed under the IBC. I am a licensed Structural Engineer with 16 years of experience, 7 of which are in the prestressed concrete industry. The reviewer received her civil PE two years ago. To date her requests for additional information have cost me two to three days of uncompensated work and she has found nothing that does not comply with the code. I am quite sure that if this was checked by the commercial side of the department it would have gone through without comment.

Some the complaints that she has is that I am not showing a calculation for every shear wall in the building. I used the stress envelope to find the controlling case and provided calculations of the analysis of that wall. this showed that minimum reinforcement was sufficient. NOT GOOD ENOUGH! GRRRRR!!! There are probably thirty shear wall segments.

 

[ash060]

I had one instance where a reviewer made me submit the computer model input file for review, so that he could check the model very unorthodox but what can you do the building offical is the building offical.

It ended up being a nightmare

But there should should always be simple solutions to complex problems

"Good design exacts a price from our egos, but it really is a gift -- it really is freedom -- to find the simplicity in things and finally to reduce an engineering design down to where it ought to be."

John H. Lienhard
University of Houston

 

[BAretired]

This is an interesting thread. In Alberta, plan checkers seem to focus mostly on architectural code requirements such as setbacks, fire ratings, fire exiting, access for fire fighting vehicles, handicapped regulations, etc.

They do not check structural design at all. Instead, they rely on the engineering seal and signature on the drawings. Structural engineers do not customarily submit calculations although the authority could, in theory ask for them. In more than fifty years in practice, I cannot recall ever being asked.

Larger engineering firms may have a checking department within the firm to carry out a design review of major projects before applying for permits, but I doubt that many are doing a review for single family residences.

I sympathize with anyone who has to go through such a process, particularly when the authority can't engineer his or her way out of a wet paper bag. On the other hand, it may cause the engineer to review his calculations more carefully, knowing it will be scrutinized by someone else.

Best regards,

BA

 

[Prestressed Guy]

Ash060, I totally agree with the statement “…to find the simplicity in things and finally to reduce an engineering design down to where it ought to be." The construction documents for this project are very clearly laid out and the details are simple to execute.

I have worked as a framer and as well as an on-site engineer for a precast manufacture. If the plant personnel did not like my drawings, they would drag me out and show me the error of my ways. That “…exacts a price from our egos” if anything does. The challenge with proper simplification of the construction is that it requires diligence in maintaining a good load path. The computation is complex so that the building can be as simple as possible.