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Re: eccentric hss braces / erection bolts

[Subject Prev][Subject Next][Thread Prev][Thread Next] I  think in most cases, the erection bolt hole is neglected in the design of
the slotted HSS braces.  Typically I have only seen one erection bolt hole at
each end of the brace by the fabricator and erector (if they use one at all).
 The fielder welder during erection will often heat up the termination end of
the brace slot (the radius end of slot) for a minute or so, which causes the
steel to expand and the slot to open up to allow the erector to slide the
brace over the gusset plate.  As the steel cools, it contracts and you end up
with a tight fit around the gusset plate (assumming the slot wasn't made
significantly wider than the gusset plate in the shop to start with which
leads to complete penetration welds to repair the oversized slots) The
erection hole is then either filled with a bolt or piece of rebar to
temporarily secure the brace in place, assumming they don't just tack weld
the brace in place and not place the erection bolts at all.  I don't think
they like to use two erection bolts because it makes it more difficult to
plumb the building prior to welding off the braces.

You can develop the net section of the brace when welding since you are
welding typically on to a larger gusset plate than the HSS brace.  If you
want to get real technical, since the slot is typically longer than the
gusset plate for erection purposes, you may have to add lap plates on the
vertical sides of the brace to make up for the lost cross sectional area of
the brace. You do have to address shear lag, which means you end up with a
longer weld by a few inches.  A rule of  thumb for weld lenghts I have often
use is twice the width of the tube (example: 5x5 tube will have four 10" long
welds) to develop the yield strength of the tube brace (AsFyRy)

Mike Cochran

In a message dated 8/8/2001 3:55:58 PM Pacific Daylight Time,
dadie(--nospam--at)bjginc.com writes:


situation - eccentric braced frame using slotted hss braces and gusset
plates.

does anybody know of a design reference or procedure for taking into account
"erection bolts"?  is there even anything to take into account?  

does it matter how much hss / gusset weld is in place (along the connection)
before the bolt occurs?

does anybody specify size or location of bolts on their drawings?

tia
da