NBCC 2010 Commentary L

[CBEngi]

Commentary L – Application of NBC Part 4 of Division B for the Structural Evaluation and Upgrading of Existing Buildings.

I’m wondering how many other Structural Engineers use this section when looking at older buildings. It’s been bouncing around the office lately, with regards to what extend and applications it’s acceptable for.

Generally I don’t see a problem with using the new Principal Load Factors based upon risk (table L-3), basically we are just reducing our USL load combinations. But other Engineers seem to make it a point to classify the building in accordance with point #18 and basically call it a day, even if in my opinion it doesn’t meet the list of qualifications. They always seem to hang there “hat” on the generality of “satisfactory performance” or “significant change”.

I’m just wondering what others do in this instance.

 

[KootK]

I use chapter L every chance that I get. Makes for happy clients and fewer unwarranted repairs. It kinda feels like cheating at times but, in reality, is based on the same reliability principles as everything else. In practice, the following make chapter L less of a free lunch than it may appear at first glance:

1) No hall pass earthquake loads.
2) Requirement to identify load path and numerically check critical details.

Most older buildings will struggle to meet this requirements without remediation. Mostly just well detailed buildings in wind dominated areas.



I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[TLHS]

I'm a fan of Chapter L. It recognizes the reality of existing structures and also gives you credit for the fact that you can verify actual weights and usages a lot better with an existing building than with proposed work.

For seismics, I'd also recommend taking a look at the Vancouver Building Bylaw upgrade requirements. It obviously doesn't govern anywhere but Vancouver, but it very clearly lays out a standard of practice for what type of work should trigger different types of upgrades. Structurally it's primarily interested in seismics, but it also talks about sprinklers and other life safety things.

http://former.vancouver.ca/blStorage/10908.PDF

It starts on page 259 of that PDF (not the numbers at the bottom of the page... the page in the pdf software)