FM 3009 turnaround bridges taking shape

Last night a total closure of I-35 at FM 3009 allowed crews to safely and quickly pour concrete to form the FM 3009 turnaround bridges.

The result: one bridge totally poured. Up next: the other bridge. 

The south-to-north turnaround bridge deck was poured last night. We'll pour the north-to-south bridge next week. Crews hope to have the bridges complete by mid-summer and in use by late summer.

Building a bridge is actually a kind of interesting process....

Once the support structures on the ground are in - that includes columns and abutments (abutments are like concrete shelves built atop a retaining wall on the far ends of the bridge) - a special crew (the guys are called "rod busters") goes in to bend the steel for the column "caps".

Column caps are shaped like an upside-down "T" when seen from the side, and serve as shelves the same way an abutment does. The steel cage built by the rod busters is set up on the top of the columns (that's why they're called "caps") and form panels are put in place around the cage. Concrete crews then fill the panels with concrete, and the caps are allowed to dry and cure.

A look (from foreground) at the back of an abutment, then a finished column cap, and a column cap with forms (center of I-35), another column cap and an abutment. These support structures will form the north-to-south turnaround bridge at FM 3009.

Once the caps are sound, beams creating the bridge span are placed. The ends of the beams rest on the shelves of the abutment and the cap, and several beams are placed a specific distance apart from one another. These beams are sometimes spaced with pieces of wood, which will be removed later. Because these beams need to be placed by cranes - which need to set up in the roadway over which the beams are being set - and because the work is happening over the roadway, we shut the roadway down. It's the only way to ensure total safety. After all, we don't want a beam being dropped on top of a car as it's passing through! (Beams are not dropped often ... but when they are, it's really scary for everyone around.)

With the beams in place, crews then set deck panels. These are pre-cast concrete panels that make up the skeleton of the bridge deck. These are typically set with crane and, since we're dangling heavy concrete over a road, we like to shut down lanes to do this. Bridge crews also build bridge forms to contain concrete that will form the total body of the bridge deck.

After beams are set - done at night with careful lane closures - the pre-cast concrete deck panels are placed. This is also done at night. The panels form a sort of skeleton for the bridge.

Finally, we pour the deck. This is the step we're on right now! After each deck is poured, we cover it with concrete and wait a number of days as prescribed by engineers that know what's going on with that sort of thing to allow the concrete to harden and cure. Once that's in place and OK, we form the barriers (we don't want anyone driving off the bridge, you know!) on either side and pour them. There are some finish items - like posting appropriate signs, making sure the surface is right, painting lane lines, etc. - and then the bridge is done!

Forms are set and the north-to-south bridge is nearly ready for concrete. All lanes of I-35 will be shut down next Thursday while crews pour the bridge deck.

In our case, we won't be ready to open the bridge as soon as the structure is in and complete. We're adding some lanes to the frontage roads - dedicated turnaround lanes - to guide traffic into the bridges. Building those lanes will take some time and will need to wait until the bridges are almost completed, as we're using the area of the new roadway lanes to access the project with heavier equipment and to store materials. That means we're hoping to have the bridges open for use late the summer, though the bridge structures may be built much sooner.

Though the picture is a few months old, the area that will become the dedicated turnaround lane can be clearly seen to the left of the existing pavement. This lane will be built after the bridge decks are complete.

For now ... expect one more total closure of I-35 at FM 3009 next Thursday night. We'll shut down a few lanes at 9 p.m. and have the whole highway closed by 11 p.m. We'll reopen the highway at 5 a.m. While the highway is closed, traffic will exit FM 3009 and go through the intersection before reentering the main lanes.

Also, expect to see some closures Monday and Tuesday nights next week as we tear down our work zone in the center median at FM 3009. Those won't be total closures, but we'll have I-35 necked down to a single lane in each direction ... and that will mean some pretty heavy delays.