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Re: Engineers versus detailers

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> From: G Vishwanath <gvshwnth(--nospam--at)yahoo.com>

> A member in the steel detailer's list
> raised an issue regarding the common practice of
> Engineers nowadays relying on "catch all" notes in
> their contract drawings that make fabrication
> needlessly costlier.
> 
> In particular the connections for beams with short
> spans are needlessly expensive when the instruction to
> design the connection for half the uniform load
> capacity is taken literally.

The comments from yourself and the other author are valid and eternal,
but not always important to a project.

Typical contracts separate responsibilities and limit the ability to
coordinate between suppliers for the benefit of the completed project.

The engineer must be generally aware of cost impacts in design but they
didn't bid on the steel supply and are more willing to be conservative
than late or over budget on their scope.

>From the steel fabricator's perspective, individual connections are more
expensive than they need to be when they are specified to maximum
possible forces. But the fabricator didn't bid on the engineering design
for the project and it is easy to call the engineer lazy for not being
more specific.

Simplistically speaking; Whether you are East or West of the Rockies,
the engineer is liable for the connections provided by the fabricator or
sub-contractor, regardless of who actually "designed" them and must take
steps to ensure that each connection design is appropriate. In some
cases the connection design is contracted to the steel fabricator, or to
an engineer affiliated with the fabricator, as part of the steel supply
contract, in which case some of the liability may flow through to the
sub-contractor.

It is not always appropriate for the engineer to give only "actual"
maximum connection forces since it is important to recognize that each
maximum member end-force may not occur in the same load case or that
concurrent members may have different controlling load cases at the same
joint. (Try designing a connection that is statically unstable because
the opposing forces from two intersecting members are not in equilibrium
at their individual maximum loads, as specified). In fact, the maximum
loads cases may not be the controlling connection design case. The
result is that a simple table can become very onerous in time and
complexity in both creating and interpreting.

Bottom Line: USUALLY it is less expensive for the project if simple
shear connections are assumed and fabricated for the maximum (or 50%)
beam shear capacity, etc. Special conditions will arise where large
numbers of connections can be reduced without significant added effort.
There is an economic benefit and all involved parties should get a piece
of that pie.

Connections designed to maximum member capacity have tremendous economic
benefits when renovation or change of occupancy use is contemplated.
(Pay me now or pay me later...)

Epilogue:
Many projects now have a pre-design value-benefit review to consider
coordinated cost-saving opportunities among all suppliers.

Additionally, coordination between design software and detailing
software is making it possible to pass specific loads and load cases
directly to connection design and member detailing. I'm not certain that
this will be a good thing because everything will be designed to the
limit of those conditions that are foreseen and unintended effects, or
poor modeling, may become more critical.

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

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