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Re: Connections

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Sub: Connections

My thoughts and opinions are:

The Structural engineer need not design all the
connections.

That would involve considerable additional work on his
part for which the compensation may not be adequate.

He could reserve his time for other tasks that cannot
be delegated.

Connection can be successfully delegated to an
engineer who specializes in it and is hired by the
detailer or fabricator.

The advantage is that the fabricator can make  choices
that suit his shop practices (without  clashing  with
design intent.)

For this to work out, the engineer has the
responsibility to give at least general specifications
for connection design. This is often neglected.

Shear Connections are possible using single shear
plates, double angle clips, stiffened or unstiffened
seats, with welding, or bolting or a combination of
both.

The engineer must indicate his preference if any,  so
that time is not wasted in correcting the shop
drawings after they are submitted for approval.

Routine connections can be taken care of by the
detailers themselves by referring to tables in the
AISC manual.

But for this, the reactions must be given for all
beams.
However too many engineers avoid this and take short
cuts by specifying "half uniform load capacity".
This results in an over designed connections.

At times the half uniform load specification results
in an impossible connection when the spans are very
small.
Instructions must be given clearly to cover cases of
short span simply supported beams so that a reasonable
connection is possible.

A table giving the number of bolts and dia and type to
cover short span beams would be convenient.

Alternatively there could be a note to the detailer
specifying that for short span beams where reactions
are not indicated, a full depth connection with A325
3/4" dia (or higher dia) must be provided. The span
(say 8') less than which beams are considered "short
span" must also be specified.

Moment connections must be sketched out in a general
way and the engineer must at least indicate whether he
prefers beams to be butt welded to the column, or a
connection using flange plates.

His preference, if any, for bolting or welding  of the
flange plates must also be indicated.
If he does not do so he must be willing to accept what
the detailer/ fabricator has chosen and not make
changes while approving the drawings.

It is necessary to indicate the moments for which the
connection is to be designed.
Too many engineers avoid this and take the easy way
out by asking for full moment capacity.

The requirement of doubler plates and stiffeners must
not be left to a detailer.
They must be indicated clearly if really required and
an effort must be made to avoid them. This effort can
be made only by the engineer. Doublers and stiffeners
are expensive and also a nuisance during detailing,
fabrication and erection. 

Axial forces in bracing members must be clearly
indicated.
Many engineers shirk their responsibilities by
specifying "full tension capacity" which results in
over kill.

These responsibilities are fully discharged by
Structural engineers in India and I personally have
gone far beyond this when I designed steel structures
in my career.

I am now associated in an advisory capacity with
detailing for US Fabricators and I must say I am
terribly disappointed with the structural drawings
that I have to work with.

Happy Thanksgiving

Regards
G Vishwanath
Bangalore, India



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