Bridge Photos from 9/11/2017 (The bridge will be slightly further along now then when I was down there on Monday but no major changes happened since then)
I went down to the bridge to check on the progress and get some updates.
The project is moving along very nicely. The crew is sticking to a mid October opening and working very hard to get it done as fast and as safely as possible.
The rebar across the deck is almost done. This also includes bolts in place that will be used to attach the guard rails. Once the rebar is done and some pieces of concrete are poured near the abutments they can schedule the concrete pour for the bridge deck. The Bridge deck will vary from 9 inches thick all the way up to 14 inches thick but the majority of it will be 10 inches thick. A total of 450 cubic yards of concrete will be poured for the bridge deck.
The engineers designed the girders with enough strength that if later on they want to refinish the bridge without removing any of the old decking they can pour another road surface on top of the old deck and the bridge can take the extra weight. I will have to confirm but I believe up to another 4 inches can be added across the whole bridge.
Concurrently with the iron work across the deck of the bridge the crew is building forms at each abutment for special concrete blocks that will connect in between each of the girders and serve to add sheer strength to the bridge. This concrete will prevent the bridge from changing from a rectangle to a trapezoid (as one of the crew members explained it to me). This concrete will be approximately 6 feet thick and go from the bottom of the girders to the top. It will not attach to the abutment in any way. The bridge will remain “floating” on its cushion of rubber.
These sheer walls will be the next concrete to be poured and must be completed before the bridge deck can be poured.
They are using an interesting technique if I remember correctly called compression sand forms where small wood boxes were built (shown in photo #3) and sand was compressed into them then the wood forms were built on top of these wood boxes full of compressed sand. Once the concrete is poured, and cured, and the forms are ready to be removed instead of fighting them all they have to do is clip the wire holding the wood boxes together and the sand inside just falls away leaving nothing holding the wood forms up. Then they just pull the wood forms out easily.
I could see looking down at the abutment that the polyurethane foam was installed on the abutment. It looked to be approximately 4 inches thick and it had a thin masonite board covering it in between it and the bridge. This foam if you recall makes up the expansion joint for the bridge to be able to expand and move in varying temperatures.
In photo number 4 you can see the structure of the bridge from inside in between the girders. The wood forms that will hold up the concrete and the red metal brackets that hold up the forms will all be taken out once the concrete is poured and cured. The metal cross beams will remain.
Underneath the bridge I can see many pen marks and notations everywhere. There are supervising engineers constantly inspecting the work looking for anything that isn’t quite right and marking it for further examination.
When I look at the plates holding the massive girders together I can see a seemingly random selection of bolts that are circled with pen. These are the bolts that were tested to ensure the proper tightness was achieved. Similar to how they test a random selection of bolts from each lot to make sure they meet manufacturing spec.
In the last photo you can see the bolts on the cross braces are not actually all the way tight yet. This is because the girders need to be able to move relative to each other. As the weight from the concrete bears on them they move and shift and if they are tightly fixed to each other this could throw the bridge off balance. Instead they leave the bolts on the cross braces only partially tightened for now then once the concrete is poured they go back and tighten the bolts up to spec.
You can see a mark on the bolt end and then two more marks on the cross brace. This tells them where the bolt started rotationally and where it needs to end up to be considered tight.
As I suspected concrete trucks will be coming soon. In the next few days they will pour the concrete for the sheer walls at the north and south abutments then towards the end of this month it will be time to pour the concrete for the bridge deck.
I can’t wait to see a solid surface on this bridge! It is coming together.
I went back recently and looked at some of my past posts. It was really interesting to kind of relive the construction process.
Cheers Everyone. More updates to come.
Caltrans Central Coast (District 5)