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Re: Connections

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Sorry for the previous incomplete posting.

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 consider the time it takes
to check the fabricators design you will spend at least as much time.  This
has been confirmed by a partner in a major east coast firm that has done
work both ways.  The difference is that in the East Coast you would spend
your time during CA checking the fabricators design.

The reality is that in California where the SEOR designs all the
connections, the SE spends essentially no time in designing simple
connections.  Each firm has their typical details and all that you need to
do is verify that the load is less than the capacity of the connection.  If
the connection capacity is exceeded it is often easier and cheaper to
increase the depth of the beam slightly and add another bolt.  In addition
if you design the connections then you save the time spent putting the
loads on the drawings.

In case you believe that you will not be liable for the connection design,
if you have the fabricators engineer stamp the connection design, I would
suggest you talk to a good lawyer.  Court cases and regulations in many
states make it clear that if you design a steel frame you are responsible
for the design of the connections.

The concept of having a specialty engineer design simple steel connections
because one does not have the expertise is foreign to me.  If you do not
know enough to design simple steel connections you have no business
designing a steel frame.  It is not as if there was any real mystery since
AISC publications make the process very clear.

The belief that you can save money if you give the fabricators a choice may
not be supported by fact.  The question comes down to whether you have an
all bolted connection or a connection where there is some bolting and some
welding.  In California all of the major fabricators have in the past
gotten together and published a document describing the relative costs of
various types of connections.  Based on this input the industry has
standardized on shear plate connections as the default connection.

I would be interested if the steel industry has done a comparison of the
costs of comparable steel projects for a project done in California and one
done in the East Coast where the fabricator designed the connections.  The
comparison should consider both fabrication and erection costs and should
be adjusted to take into effect the different wage rates in the two
markets.

I believe that there are other factors that may make it more expensive for
the fabricator to design connections.  First is the fact that the
fabricator has to pay for an engineer to design and stamp the steel
connections.  On an east coast project I was involved with the decision was
made to have the SEOR design the steel connections in order to eliminate
the time needed for the fabricator to design connections and to have them
approved prior to fabrication.  Remember time is money.

There are also situations where while it may be cheaper to fabricate a
bolted double angle connection, it is cheaper to erect a shear tab
connection.  Given the prohibitions by OSHA on back to back double angle
connections the savings in erection costs are probably even more.

The bottom line is that having the SEOR design simple steel connections
makes a lot of sense no matter how you look at it

Mark Gilligan SE

++++++++++++++++++++++++++++++++++

> 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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