Modeling of the deck support of a bridge deck on piers with double shafts.

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A recurring query received by our technical support department is related to the modeling of the support of a bridge deck on piers with double shafts.

When a deck with a large width is supported on piers with double shafts, it is essential to be able to model the effect caused by the torsion of the deck on each of the shafts. The torsion of the deck, since it is a moment around its longitudinal axis, will cause one of the shafts to be tensioned and the other to be compressed.

The solution is based on using two tools that we find in the dialog box of the member attributes:

1.- The eccentricities.
2.- Joints at the ends of the members.

With the first one, we will get the top nodes of the piles to be connected to the node of the bar of the deck and, with the second one, we will be able to edit the way they are connected, which will allow us to adapt those connections to the characteristics of the support devices that we will have in reality on each of the shafts.

With the help of the following example we will indicate the steps to follow:

1.- We introduce the board. In this example, we are going to define a panel with a box section:

2.- Insert the batteries - THIS IS WHERE THE TRICK IS!

The batteries must be inserted connecting the base of each one of them and the knot of the board where they should arrive:

3.- We give eccentricities to the ends of the piles that coincide with the board until they are in the position we need:

4.- Finally, we edit the joints of these two ends according to what we need depending on the characteristics of the support devices:

If we introduce in our example the following eccentric load:

We can see that the effect of the torsional moment of the deck is transmitted to the piles by pulling the ones on one side and compressing the ones on the other side:

Having thus obtained a model that will allow us to analyze the effect we will have in reality on our two shafts.

Finally, we would like to emphasize that, with the procedure described in this article, we avoid using auxiliary elements such as infinitely rigid bars, which dirty the model and make it much heavier, resulting in a much more optimized and elegant model.

As you can see, in this model, the support of the board is modeled on its lower face. We invite you to read the article (by clicking on the following link) that we have published in our help center dealing with this subject to complete the information:

- Model correctly in STATIK the support of a board on its bottom face when the sections have axis point on the top face.