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Re: Connections

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I would like to offer some thoughts on the concept of the fabricator
designing connections.

It is suggested that the engineer can save fee by delegating the design of
simple connections.  The reality is that if you con

> 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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