Bill Mankin and High Steel Structures - Innovation at work
Bill Mankin at High Steel Structures in Lancaster Pa, sent email, indicating
that his team would be in Charleston for drilling and reaming of the final
center edge girders that join the east and west main spans. I was curious how
the designers knew exactly how long to make the center edge girders and I
learned that they do it the old fashioned way - they measure. So after the
center edge girders were cut to size, they were temporarily spliced to the
last anchor girder. The center girder was then drilled and reamed to
exactly match the holes in the splice plates.
The worksite at the old Navy Yard
Part of the team
The rest of the team
Where is the midpoint of the bridge platform? Locate the vertical stiffener
between the two splice plates below. This vertical stiffener is in the
middle of the center girder (which joins the west and east platforms) and
will correstpond to the highest point on the bridge deck as well as
being the exact center of the main span.
The center edge girder is temporarily
attached to each of the shark fin (anchor) edge girders. The holes in the
splice plate were undersized and now are being reamed to the correct size
The bottom of the junction between the anchor edge girder and
the center edge girder is attached by a splice plate that runs the length of
the center girder.
The wide one is for the bottom and the two narrower plates are for each side
of the upper part of the bottom lip.
These plates will be attached to the bottom of the nearer anchor + center
edge girder and look similar to the far edge girder (with splice plates
already attached)
Before attaching, though, an inspection is in order.
Hmmm, something looks asymmetric - and we know symmetry is essential. Perhaps
a missing hole? hmmmm the collective search from our team is on
Hmm - found it - marked it and applied the center punch
Making a hole (with the drill off) - and making the hole with the drill on
End of George's tale of the missing, but found hole
Next phase. Although the holes for attaching the vertical splice
plates have been drilled, they were drilled undersize.
Now that the anchor edge girder is attached to the
final splice girder (that will eventually couple the east and west platforms),
the splice plates are temporarily attached with drift pins (conical shaped
1 foot rods seen extending beyond the rectangular
splice plate in both the left and right photos)
and the holes reamed to the correct size.
One girder done, now start reaming all the holes on the
other girder
Driving a drift pin to align the plates
Hmmm - everyone seems to know what to do except the guy on the right -
our mysterious 6th member of the team
I always wondered how you could build a bridge several miles long and have
it perfectly meet in the center. Well, attached to the last anchor
edge girder (looks like a shark fin) is the center edge girder that is much
like the keystone in an arch. It represents the center of the main deck
and also is the highest point of the deck. It was originally cut to within
a few inches of the correct length (about 10 feet). The length has now been
reduced to perfectly link the east and west decks.
Here you can see the joint between the shark fin girder and the
center edge girder. Note the extra spacing on the left between the 1st and
2nd column of holes. This has to be matched with the holes in the upper
and lower splice plates. Here is where High Steel does their thing -
laying out the hole centers, drilling undersized holes, attaching the
splice plates to the shark fin girder and the center edge girder with
drift pins and then reaming them to size.
Now here is the matching top plate - drilled perfectly to match the
edge girder hole pattern. So it all really really works like a symphony -
each instrument has its part and the conductor directs the parts to
play in perfect harmony. Note that the holes on the left are smaller
than the ones on the right. When the plates are attached to the center edge
girder, they will be reamed to the correct size.
And now a short aerodynamics lesson. The wind load on the central section
of the brige can create a potentially huge torque on the east and west pylons.
So wind shields were designed and are placed on either side of the
platform along the length
of the center section of the platform (where the east joins the west platform).
On the north side, a different wind shield is used as shown here
and attached to these mounting brackets seen along the length of the
north edge girder
Finally, how to we move the girders from here to there? By
barge of course. Here it is waiting with floor girder in place
