|The Lake Pontchartrain Causeways have a lot of spans and piers.|
Designing these piers requires looking at a large number of different loading patterns. What if there's one truck pushed all the way over to the side of the road here, and no others? What if there's one at the edge, but then one spaced 15' closer to center? What about the wind loading? What direction? For Greenfield, I calculated (using some programming code I wrote, not by hand) around 50,000 different loading cases. It doesn't scratch the surface of the number of possible combinations you could check under the code. In fact, I calculated that if I checked every load placed to the nearest foot only, that it would be approximately 10^21 different combinations.
|The columns are built to connect into the footings below (see To Build a Bridge Part IV: A Firm Foundation). The rebar sticking out of the footing that now forms the column had to be placed before the footing was poured, so it's critical the shape and height are right, which can be hard to measure for thin pieces of steel sticking 20' in the air and moving around.|
|These are considered "slender columns", and for them, the total amount of vertical load will actually be critical.|