This chapter will walk you through the steps for modeling a mat foundation, also known as a raft. Alternative metric values and units are identified in square brackets [ ] next to the US units. The metric values are not exact conversions. The code used is ACI 318-05.

For information on creating a new file, see Creating and opening files . You should ensure that you select mat foundation in the new file dialog box.

Most mats support columns and walls. You may choose to model the columns and walls but you should be aware that this could affect the mat behavior. In particular, if there are lateral loads then you should be very careful in defining the supports above as having no horizontal restraint. Otherwise, the supports above rather than the soil (springs) below could resist some lateral moment and shear.

A mat need not have columns and walls modeled above. The reasons to model columns and walls above include improving the appearance of the model, and providing snap points for point and line loads. Additionally, a wall above will stiffen the mat in a beneficial way.