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RE: We're Not Getting Older, We're Getting DUMBER [WAS: Any Young Engineers Out There?]

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I'm almost hesitant to enter the fray, but here goes. We recently authored a paper for Wood Design Focus on this topic. Here's a link to the PDF:
Here are some excerpts:

The question is often asked, "Why switch to LRFD?" The answer really lies with the designer. The wood industry now has provided a dual format NDS to give the user the option of using either methodology as transparently as possible (Line et al. 2004). Universities have predominately been teaching LRFD for the last decade to engineering students, so young designers may have a certain comfort level with LRFD.

One benefit of LRFD is the convenient use of common load sets regardless of the structural materials used. When designing hybrid structures involving wood and other materials; the designer now can use one set of loads for LRFD, instead of switching load sets part way through the structure as required by a structural material change that might have an LRFD or ASD basis. Most structural materials now have the availability of resistance values and design processes on an LRFD basis. However with LRFD, since deflection analysis still requires unfactored loads, both factored and unfactored load sets will be required to provide both factored and unfactored load paths through the entire structure. The bottom line is that the designer can choose the methodology that best suits his or her needs. LRFD makes the design of structures using multiple materials more convenient.

Load factors can contribute significantly to differences in design results using LRFD versus ASD. In many cases, more economical designs result using LRFD procedures. The underlying premise of load factoring is to move more of the safety factor, or reliability, to the loads side, since more information is available on loads today. It is reasonable to expect that more efficiency in the design process results from this knowledge.

Designers of multi-story wood-frame buildings might consider the LRFD approach where multiple transient live loads could result in significant efficiencies. For applications with numerous structural elements, such as headers, this could result in substantial savings.

OK, now I'll duck and cover.



John "Buddy" Showalter, P.E.
Director, Technical Media
AF&PA/American Wood Council
1111 19th Street, NW, Suite 800
Washington, DC 20036
P: 202-463-2769
F: 202-463-2791

The American Wood Council (AWC) is the wood products division of the American Forest & Paper Association (AF&PA). AWC develops internationally recognized standards for wood design and construction. Its efforts with building codes and standards, engineering and research, and technology transfer ensure proper application for engineered and traditional wood products.

The guidance provided herein is not a formal interpretation of any AF&PA standard.  Interpretations of AF&PA standards are only available through a formal process outlined in AF&PA's standards development procedures.