Return to index: [Subject] [Thread] [Date] [Author]

Re: ASD vs LRFD

[Subject Prev][Subject Next][Thread Prev][Thread Next]
> From: "Cain, William" <bcain(--nospam--at)ebmud.com>

> Roger appropriately points out that serviceability issues often dominate the
> behavior we are trying to achieve.  I have to laugh when I see the
> pronouncements about how much more accurate LRFD is than ASD and how "we"
> can understand the structure so much better. When you start from the same

Serviceability is also a limit state. This seems to have been forgotten
in many of the postings here. In practice, there has also been some
confusion of serviceability vs LRFD coincident with evolving acceptance
of computerized design optimization, higher strength materials and
proprietary structural components.

> From: Roger Turk <73527.1356(--nospam--at)compuserve.com>

> there *may be* occasional, unanticipated overloads, or that the material
> strength is less than what was assumed in design and/or specified.  Look at

So, LRFD simply separated those two conditions to allow control and
monitoring on each.

> From: Christopher Wright <chrisw(--nospam--at)skypoint.com>

> The ASD design margins provide satisfactory service, which is reason 
> enough for considering them valid figures of merit. I doubt that 

This is true when the entire structure is made of one material and one
trade. As we progress into an era of composites, would it not be easier
to have a way to integrate design between all materials and construction
practices?

> From: "Laurence B. Oeth III" <viacalx(--nospam--at)europa.com>

> We now need to run a strength analysis and deflection analysis.  Perhaps

You weren't doing this before? The requirement for analysis will always
be based on engineering judgement.

> Concerning conrete design, ASD vs. USD:  I design many water retaining
> structures, wherein crack control is the key, not strength.  ASD rules,
> although cookbook factors to design with USD do exist.  I need to know
> both methods but wish my mind was filled with other more interesting
> topics than two redundant ways to design the same thing.

Deja vu!!!! See my comment above.

-- 
Paul Ransom, P. Eng.
Civil/Structural/Project
Burlington, Ontario, Canada
<ad026(--nospam--at)hwcn.org> <http://www.hwcn.org/~ad026/civil.html>