We’ve all driven under or over bridges as we travel on interstate highways. Here is what the bridge looks like while being constructed. These steel beams are about 90 feet long, each, about 10 feet high, and weigh about 90,000 pounds. They will be spliced together to span a length of about 130 feet.
The interstate highway was closed in 15 minute increments between the hours of 11:00 pm till 5:00 am to allow the contractor to install the beams. In 15 minutes they had to lift the beam, place it in position, and bolt it together enough so it was stable and would not collapse. The interstate was then opened for a minimum of 15 minutes while the contractor prepared the next beam for installation.
After the beams are installed and stabilized, the deck will be constructed, and you and I will be able to drive across it.
I am a retired civil engineer, currently creating a children’s interactive picture book titled “Have You Seen My Daddy’s 18 Wheeler?” While inspecting this bridge being constructed, I wondered how many 18 wheelers passed me. I also wondered how many 18 wheelers my family and I passed on our travel vacations from Chicago to Hilton Head Island, or Williamsburg, or Yellow Stone, or Orlando.
But, inspecting the bridge construction gave me the money to do that, so let’s look at it some more. After the beams were installed, the contractor installed a total of three decks, two temporary wood decks and the third was the final concrete deck. Here is what that process looks like.
The first temporary deck is called the Protective Shield and is installed to prevent objects from falling onto the moving traffic below.
The “False Deck” is above the Protective Shield and supports the finished concrete deck as it is being poured, until it cures. Both of these decks will be removed prior to completion and acceptance of the bridge. The False Deck makes the final adjustment between the beam and the correct finished deck profile. That final adjustment is called the “Fillets”.
The concrete is connected to the beams with steel studs, welded to the beam. The elevation of the plywood planking is correctly adjusted to meet the proposed roadway profile.
The above process is what creates a bridge that we commonly drive across or under.