Ah, I see. I tend to think of the ASCE 7 as a balancing act between ease of implementation and economy of design, but you make a great point about the importance of transparency. I would argue that the current live loads are very easy for engineers to use (aside from those pesky load...
While I understand the pros and cons of ASD & LRFD, once AISC combined them into one manual, the differences began to disappear to all that remains is a conversion between the two. What is the load and what is the capacity? Well, that depends... the public (or client) demands a clear answer...
Ron, I appreciate the thorough explanation, and I'm sorry for not responding sooner. In fact, I wish this timeline was part of my undergrad curriculum. Only after entering practice did I realize how little I knew about ASD, and how much my understanding of design loads and limit states...
James, Thanks for the response. You make a good point, but for environmental hazards, the safety factor lives in the return period to establish uniform risk. For example, I'm told that snow loads in ASCE 7-16 and earlier resulted in dramatically different probabilities of failure across...
Chad, Thanks for the thoughtful response. It's certainly true that we wrap a lot of big questions into our floor loads, and it may be true that the public cares more about minimizing risk from human-imposed loads than minimizing risk due to external hazards like earthquakes. That's hard to...
Thank you, Ron. I'll look out for that announcement. Does anyone have an opinion either way about the IBC vs ASCE 7 approach to service wind? Using a fixed factor is simpler, but ASCE's MRI method ties the drift check to more tangible performace objectives. -- Christian Parker P.E., M.ASCE...
While live loads are defined, they are still unknown. A heavy piece or furniture could be considered a live load, such as a piano. The other consideration is impact, if I am in my basement and one of my kids jumps off the couch, it is like an earthquake overhead! There is still a place for...
In my professional opinion, "uncertainty" is the key word when referring to the "MINIMUM" Design Loads for Buildings and Other Structures coupled with simplified analyses. ASCE states that "it does not intend, nor should anyone interpret, ASCE's standards to replace the sound judgment of a...
Christian, As you are likely aware, the road to LRFD has been a long one, with some recent updates. The road starts back in the 1960s, when ACI introduced "Strength" design as an appendix in 318-64. In 71 this became the primary method and ASD moved to an appendix. Steel was next, in the...
Christian, as you note the 0.42 factor in IBC is historic and ties back to ASD design. The ASCE 7 committee has not discussed updating this in IBC, but it could become a topic of discussion for the ASC 7-28 Committee, which will be formed in a few months. Look for a call for volunteers...