Expectations of the Professional Structural Engineer

[higy1]

I Design and Build Timber Frame Homes. I am an engineer but not certified. The Owner picks the structural engineer for analysis. I use beam tables and rules of thumb for the initial design before the approving engineer is involved. I have noticed wide variation in what the engineers "check" or analyze for their approval. Of course they cannot check every joint or beam as the price in a large timber frame would be prohibitive. I have asked several why they check what they do and I never get a really good answer, they seem somewhat intimidated that the lowly timber framer is asking such a question.
Is there a standard or guideline as to what level of analysis is required for approval? I have been unable to find one. I understand the code requires snow load, floor loads, seismic loads, wind loads etc, but these loads eventually end up in individual beams, posts and joints. Some check the "critical" beams posts and joints trusting me for the rest while others check much more. Any insight would be appreciated. Thanks in advance

 

[PenneEng]

In general when an engineers reviews and stamps the job for approval they are overall taking responsiblity and their future could be at stake if negligence is found. Not only is the beams or columns or building element important but so is the connection. Some engineers are more particular while others may feel comfortable with experience. The difference is size could be how much they deem safe. Some people design to 99% capacity while others leave room for future expansion. It's all engineer judgement if there is a such thing. Others realize there is safety factors in design loads, materials used, and probablity. It's all engineering judgement. Find an engineer you feel comfortable with and grow your futures together. Back to the engineering judgement; some have it some do not.

 

[csd72]

Yes, I would agree that this is an engineering judgement think. Less experienced engineers need to do numbers on everything, more experienced engineers often just know what works.

Also there are quick ways to check sizes relative to each other. Checking the worst case and using simple rules to compare the less critical members can be done with simplified rules and judgement.

Structural engineering is often more an art than a science.

 

[MiketheEngineer]

I usually look at worst condtions and go from there. If a 2x12 can carry the load then I know a 4x12 is OK. Same with columns - if 6x6 works - why check an 8x8 with same approximate or less loads.

Then pick a few critical joints. Check them - set a minimum type and size connection pattern and you are good to go.

That may be where experience comes in...

 

[rscassar]

The engineer who stamps the drawings will be ultimatley responsible for the project. Like yourself, I also work under the supervision of a professional engineer who when they first hired me would look over my designs and calculations like a hawk. But now that they have installed good design habits the checks are less thorough.

Personally I do not like engineers who are prepared to stamp anything which is submitted in front of them. I have been having many disputes lately with truss engineers who in my opinion have been doing this.

But with time, a compentant engineer who has designed many timber frame houses will know intuitively whether the sizes seem right by feel. Much like an excellent wine maker will know when the grapes are right to make a good wine.

 

[TXStructural]

In Texas, it is illegal for me to seal drawings which were not developed by me or someone under my direct supervision. If you give me a set of plans and ask for a review and seal, and you didn't design them under my supervision, I have to check everything. To do otherwise compromises my name and defeats the purpose of the engineering license. The state routinely sanctions engineers for "plan stamping".

If I were familiar with the type of structure, I would check for things I know get overlooked first. At a minimum: loads and specifications/general notes, member layout, load paths, design scheme, lateral system, member sizing for typical members, then all atypical members, connections, fasteners, anchorages, foundation. Compatibility of deflections on rigidly connected members, deflections, and other serviceability also have to be reviewed.

Most likely, I'd have to spend a significant amount of time figuring out how the design decisions were made, so I know how to assess the validity of the design. It is not "is this member the right size?" It is more like "how is the load going to move through this structure and get to the ground?"

 

[csd72]

I have never really understood that rule. supervision does not necesarily ensure the integrity of a design - only a thorough check will do that. Yes, you will be more familiar with the reason for the design decisions but you will also be subject to possible contagion of logical errors.

I always believe that the best way to check a design is to ignore the calculations and check the drawings independently. Few structures are that complex that they cannot be understood easily by an unfamiliar but competent checking engineer.

That said, I agree that an engineer should not stamp drawings that they have not checked.

 

[TXStructural]

I think the idea of "direct supervision" is that you are familiar with the work practices (in the old school, you actually taught those practices to your subordinates) and would be checking the work as the project progressed.

When I started, I was walked through the loading of a structure, given input and feedback on the layout, and calcs were checked as I went along. It was more process control than QA inspection.

 

[csd72]

Yes, thats my point. Just because an engineer knows the proper process to design something does not mean that they are not going to make mistakes.

Out of all the structures that I have checked I have always found mistakes. The mistakes are normally smaller the more experienced the engineer, but they are still there.