|Jackhammers demolishing the deck of the old, Greenfield bridge|
The first step to building the new Greenfield bridge is getting rid of the old one. The new bridge is going to be bigger, and built to an updated code, but there was already a bridge there. It will be down for about 6 months while the new one is put up. This is fast, but does not really fall into the realm of "accelerated bridge construction" (ABC). I just means the crews will be working a little harder, or with a few more people on staff to get it done.
|A look at the equipment and the bare girders behind it with the deck stripped off.|
|After night one: the girders over the interstate remain as well as the piers. The old deck with its rebar is sitting in the foreground waiting to get carted off.|
Most bridges people know, or think about when asked are long, impressive looking ones. These are often referred to as "signature" bridges. A signature bridge is one in which a lot of extra money is put in to make something unique and beautiful. They can be shorter if they're in a prominent location and the powers that be want a specialized look (an example from my neck of the woods is the Milwaukee art museum bridge). Some bridges can't help but be signature-style bridges due to their immense length.
Most bridges, however, are not signature bridges. They are designed to be as cheap as possible, with maybe 1% of cost added to make them look vaguely appealing to the public. That aesthetic improvement typically coming by adding relief patterns to the columns and staining the whole thing what are deemed to be pleasing colors. Thought is given by the designer to how things will look, but that isn't likely to be a controlling factor unless the cost and construction considerations of the choice are essentially zero. And that tends to only be true for details that the public is unlikely to notice.
|The old, steel girders with shear studs that used to connect them to the deck.|
|The shear studs are designed so that when the girders bend, the concrete above would bend with it, thus you can take advantage of the added strength of the deck when designing the girders and save money on steel.|
Most states use prestressed, concrete girder bridges in this range. A few with big steel industry in their state will use steel girders. Wisconsin does not have a big steel industry so concrete girders are used in this range. All bridges are made out of steel and concrete. There are a lot of fancy materials out there, but nothing can compare to steel or concrete for their strength-to-price ratio. Other materials are used in small capacities (like using rubber to seal joints to keep water out) but structurally it's always concrete and steel.
Each material has different ways it can be used. Very short bridges are normally "slab" bridges. Essentially the deck is made strong enough to carry the whole load without any girders beneath. Then you get to traditional girder bridges like both the old and new Greenfield bridge which have these girders running the length and supporting the deck above.
As the spans get longer, the girder shapes change. A typical girder is shaped like an 'I' (see the above pictures), a thin 'I' if it's steel, and big, overweight 'I' if it's concrete. Longer spans, or ones with horizontal curves (and some very highly skewed bridges) will switch to "box" or "tub" girders. When you start to get above 250 feet you start to get into fancier and fancier systems, moving away from girders entirely.
But Greenfield isn't fancy. It will be wide, but it's a work-a-day bridge and so it will use, as much as possible, all the standard, WisDoT features of a normal length bridge.