Changing the face of Charleston : The unbuilding of the Grace and Pearman Bridges
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(Mar 27)
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December 16, 2005:
Dropping Pearman supports M1 - M5

Today was really fantastic. Mickey, Ken and their ABS team rigged Pearman supports M1-M5 to ignite sequentially, at 200 msec intervals. Just like clockwork - it happened. This time after the event, I immediately turned on the write protection for my video. Not another "senior moment" of disaster this time! Watch the sequential motion of the tops of the supports as they collapse.

Starting out at the base of the Grace Bridge, we checked the progress of unbuilding the Pearman supports in shallow water. For the past week a jack-up barge was used - but for the past few days, Michael and his 1250 on an "ordinary barge" have been unbuilding the supports. Here is Michael and his 1250 actively unbuilding

However, with Tina looking on, its time for a break, with the 1250 arm retracted

The context of watching the unbuilding of M1 - M5. Under truss 34 on the top of the Grace support here is probably the last ever photo of the underside of the Grace Bridge looking west. I am entranced by the shadows of the Ravenel, and Pearman (left) and the Grace (right) on the surface of the Cooper River. Pio, Richie, Brad and Speedy have been rapidly removing the Grace roadway surface - so sunlight, for the first time since the late 1920s has penetrated the Grace (look at the area just above the concrete support in the middle of the photo.

Pearman girder harvesting is in full swing and a load is on its way, probably to Nucor - here you can more clearly see the current location of Grace roadway harvesting.

Looking east, the sunlight is not yet able to penetrate Grace's surface and there are no Pearman trusses to cast their shadow. To the right, you can see the roots of M7 and M6 (recently removed by the machines on the jack-up barge) and the to-be-imploded M5, M4, M3 and M2 (M1 not shown)

My photo spot with double reduntant video (Mickey's and mine) and my D70. The white cord you see hanging down between the tripods is our 100% tie-off - to prevent Frank from kicking the tripods with cameras over the side.

The fusing and line linking M2 with M1 which provides the 200 msec delay between M2 ignition and M1 ignition. For a better view of the fusing, look at Loading D-25

And the real thing: this is the control (before)

about 400 msec later. M5 ignition walks up the columns and M4 ignition has walked half way up the columns

about 800 msec later. M5 and M4 ignition is complete, M3 ignition has yet to reach the cap, M2 ignition is about half way up and M1 iginition has just started (a small puff at the bottom of M1 (right most columns). Note that the cap of M5 (the left most column) has started to drop as the columns collapse. Note the red area just above the cross member on M1, the right-most column - indicating preignition.

Now you can see the left edge of all the caps progressively drop as the supporting columns collapse. In addition, a water wave is developing around each base and moving outward. Also note the containment of debris - very little horizontal movement of pier fragments.

Continued downward movement of the pier caps - as judged by the cap edge positions. Note puffs of white cotton balls are forming over the edges of the M2 the cap (overlapping the base of the Motley Rice building in the background)

Here M5 (left most column) has completed its collapse while M1 (right most) has lost about half its height

Here, M3 and M4 have finished their collapse

and here only M2 and M1 continue their downward movement while the M2 cotton puffs remain stationary.

and its all over.

Note that the cotton puffs above M2 have drifted a little to the south based on using the Motley Rice building in the background as a reference. Not a lot of wind today - at least over the past few seconds.

more of the same and then all the cotton puffs

begin to dissipate

And, as my dental colleagues would say - only roots of M1-M5 remain

Ignition and collapse: Selected video frames

(click image to enlarge)

Initial ignition of M-4 (time = 0)

M-5 detonation and progression of M-4 ignition (time = 400 ms)

M-4 detonation (base) and M-4 ignition (top) (time = 760 ms)

M-3 detonation (time = 1.25 sec)

M-2 back detonation and M-1 ignition (near the cross member)
(time = 1.72 sec)

M-1 base detonation and ignition near the top (time = 2.34 sec)

M-1 base detonation and cap ignition (time = 2.67 sec)

Collapse of M-1 - M-5 (time = 4.36 sec)

continued collapse (time = 4.85 sec)

continued collapse (time = 6.5 sec)

And a photo of me - Ellen wanted to see where I was (this time)

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Attribution: C. Frank Starmer and Sparky Witte from