Engineered design question

[Sifu]

Probably opening a can of worms here but I need educated. I have an exterior wall, +/- 20' tall and 20' long, full of openings. Engineer gives a set of general notes indicating he is designing the walls of the house to any of 5 of the prescriptive methods he lists. He does not indicate which walls meet which prescriptive method. It is easy enough to identify which walls meet which method except that the tall wall does not meet any of them. I asked for him to identify which method and how he intends to satisfy the particular requirements of the method. The response was that the tall wall is not a braced wall, therefore no method or requirement for bracing. Is this valid? I was under the impression that while a DP can design methods other than the prescriptives in the IRC to comply with the intent, he could not do away with the intent. My boss and plan reviewer disagree, and they are pretty sharp so now I don't know. I understand that 602.10 states that where a portion of the building does not comply with any of the prescriptive provisions, that portion must be designed. I guess my question is does using the engineered design allow for this wall to be ignored as far as the wall bracing requirements go. I am not really arguing this point with a sealed design and a response in my hands, I am wondering if my notions have been wrong about what a DP can or can't do.

 

[JBI]

'Designed in accordance with accepted practice' is more than drawing a picture and notes.

Design requires calculations.

Calculations are broken down in the design methodologies - Allowable Stress Design, Load and Resistance factor Design, etc.

If it is prescriptive you simply follow the path in the code. If it is not then the method used should be identified and calculations provided. If not with the application, then upon request. IF the work was done there is no reason to withhold it.

 

[Phil]

Without the tall wall, does the building meet all of the requirements for wall bracing? (I have only done engineered shear walls, so I don't know the IRC braced wall line lingo and requirements) In other word, if the tall wall is replaced with posts and a beam/header, would all of the IRC requirements be met?

 

[Keystone]

Post and beam would require DP.

 

[steveray]

If it is an exterior wall, it is most likely a braced wall....If he is stamping a design and it is detailed enough for you to inspect it to that very specific design, great. If it is just some crap drawing, grill him...

 

[jdfruit]

A lot of unknowns on the actual structure; however generally I agree with Sifu that the 20ft tall exterior wall should be "designed" by the Engineer, not ignored. If not part of the bracing necessary that is inline with the wall you still have wind or seismic loads perpendicular to the wall in addition to vertical bearing loads. Stud walls taller than 10ft require combined loads for vertical and lateral be analyzed so the studs do not bend too far out of the wall plane; if they do, the results can include partial collapse.

 

[mtlogcabin]

Table R602.3(5) allows a maximum height of 10 ft for bearing walls that are unsupported laterally. Non bearing 2 X 6 walls can be 20 ft laterally unsupported

a. Listed heights are distances between points of lateral support placed perpendicular to the plane of the wall. Increases in unsupported height are permitted where justified by analysis.

Seismic zone D, high wind areas and ground snow of over 70 lbs will require engineering.

Ask for fastener details and calculations.

 

[Sifu]

The wall is "designed", as the entire structural drawing is a sealed design. My suspicion is that either the wall was not built as the designer intended it, or the designer accidentally excluded the requirement for bracing. The response I expected was some sort of revision based on one of my two suppositions. Instead I got the response that it is not required to be braced. That is something I believe the code would not support. My superiors believe the designer has and can disregard the requirement for bracing since he "designed" it. The question remains- does "accepted engineering practice" allow for the code to be disregarded in this manner? Maybe some of the DP's can help me with this. I am not challenging the expertise of any DP, more so challenging my own assumptions.

On this plan and many others I often see the DP reference a code section, either word for word or by actual book and numerical reference instead of inventing his own, for example: "garage wall to be constructed as method PFH, see IRC 602.10". For this plan he actually references 5 different wall bracing methods for the entire structure but like I wrote in the OP he does not identify which walls should employ which method, nor does the wall I questioned meet any of them, or any other one of the prescriptive methods.

 

[JBI]

'Design' is more than a drawing, it requires calculations.

The Code provides a prescriptive path that is one way demonstrate compliance.

Non-prescriptive elements must document how the meet the performance requirements of the Code.

Allowable Stress Design is a methodology that is considered 'accepted engineering practice', it requires calculations.

Ask for the design methodology and calculations.

 

[jdfruit]

There could be a standard of care or minimum competency required for registered Engineers in your state. A call to the registration board with your question could be a good idea.

 

[ICE]

A call to the registration board with your question could be a good idea.

Or a really bad idea.

 

[Francis Vineyard]

Why are you suspicious?

Is it not the inspectors responsibility to verify the contractors constructed the structure in accordance with the approved plans?

The Building Official may require or the adopted code requires braced walls be identified and located on the construction documents.

To my knowledge the DP must use the referenced standard in R301.1