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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

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Attribution: C. Frank Starmer from