Bridge Photos by Kyle Evans, 3/15/17
Great shots, Kyle!!
I thought you might like to see this non-technical explanation about what CT is doing at the bridge from Kyle Evans:
I apologize everyone for the delay. I got home and had dinner then spent time with the family. Finally everyone is in bed so now I can start to work on my photos and video from today and offer this explanation.
A big Thank you to the Carmel PineCone who facilitates me being able to be there to take photos. And a big Thank you to the CalTrans guys who are so accommodating to me answering questions and helping keep me safe while I take pictures.
Disclaimer: I am not an engineer and this is my best interpretation of what I saw and the information given to me by the CalTrans engineers that I was talking to.
The bridge is coming down. It isn’t violent or quick however when it reaches that tipping point it will go quickly. The big drop that you saw in my first photo happened quickly after about 10 or so hits when they broke the seam between the north most section and the middle section.
A little bit about the bridge construction. This will be relevant to why they are demolishing it this way.
This bridge was built in pieces. First they made the foundations, then the columns, then they formed and poured the bottom of the bridge. Once that was done they formed and poured support ridges running the length of the bridge but in order to save on weight and materials the majority of the bridge is hollow. Then they formed and poured the top deck of the bridge. They couldn’t get the wood back out of the interior of the bridge so that part of the form stayed.
Over each column instead of being hollow they made the bridge solid concrete. This helps strengthen the bridge and its connection to the columns.
This construction of the bridge effects how they hit it, where they hit it, and how hard they hit it.
Another piece of relevant information is there is no safety quick release on the wrecking ball.
Lastly they are very carefully trying to get the bridge to fall uphill away from the park, away from the steepest part of the canyon and away from the power poles that are very close to the bridge. The power poles by the way are why they can’t swing the ball in from one side and the desire to get the bridge to fall uphill is why they don’t swing in from the other side. Straight up and down is the name of the game.
Going back to the bridge construction. If they hit over the solid concrete parts the ball seems to do very little visible damage and bounces off the bridge but it is deceptive because that allows the majority of that force to transfer down into the foundation of the bridge and does more to move the bridge and shift it towards its tipping point. It also does more damage to the column under the bridge. When they hit over the solid part chunks were flying off the bottom of the bridge.
When they hit the hollow part of the bridge it does more damage visibly but does less to get closer to the end goal.
This is why they are not dropping the ball from a very high point. If they dropped the ball from too high and missed the solid part of the bridge they run the risk of punching a hole through the upper deck and if that happened the ball might get stuck in the bridge completely. Without a safety quick release there would be no way to get the wrecking ball or the crane unstuck.
Also they don’t want to do to much all at once because if the bridge shifted in the wrong direction from a hit they want to be able to correct this action.
While I was there they were hitting around 10 times then surveying the bridge then making recommendations on where to hit then adjusting the hit location.
In addition to that while they are surveying to figure out where to hit next the crane operator has to swing the wrecking ball out over the canyon and lower it down to unspool the wire. Over time the wire becomes crossed and not spooled correctly because it is going in and out rapidly. This has to be corrected or the whole thing could bind up. They unspool into the canyon then slowly bring the ball back up making sure that the wire re-spools properly.
There is a spotter on top of the crane at all times communicating with the crane operator about the status of the spool.
While I was there they focused first on breaking the deck surface between the north most section and the middle section of the bridge. They did not cut the rebar between these two sections because they want the weight of the north section to help pull the middle section of the bridge down. Then after that they started hitting the bridge on the uphill side as close to the railing as they could directly over the north column.
This was causing the column to sink further into the hill and lean more and more uphill. The bridge should fall that direction if that operation is successful.
They are hoping that the bridge will not go more than one more day like this. Judging based on the north most section and how much it moved suddenly they could be dropping the ball on it for the better part of a day with very little visual change when suddenly the bridge will give way and collapse. We just don’t know exactly how it will play out right now.
Hopefully when it finally does go it falls in the way they want that will make clean up easier, and it falls in a way that is safe for all of the workers and machinery involved.
I also found out more details about the part that had failed before. First they dropped the height of the crane arm by about half. Second the crane had a specialized part that would allow it to drop a weight in free fall. This part had never been utilized before. The CalTrans engineer described it as being like having a 4 wheel drive vehicle that you never used 4 wheel drive in before. Then when you go to use it you realize that it is broken. That is what happened with this part. So they had to order a replacement part and have a crane engineer install it and make sure it was functioning.
Now they are up and running. This operation is very dangerous to the crane operator and quite hard on the crane.
This is a much more precise operation than I ever imagined and there are so many variables involved.
I will try to get more information tomorrow and I will try to get my photos and video from today processed before I pass out.
I hope people find this very long winded explanation interesting or at least informative.