How do you calculate the volume of trapezium footing?

Answer 1

Not sure exactly what you want but our garage was built a few years ago with a trapezium base (to fit the land space available to the side of our house).

The footings were a fairly normal trench style with deeper parts at the corners and under the rear doors' pillars location (our garage is about 9 ft wide at the front but about 18 ft wide at the back). The volume of these footings were the volumes of the cuboids along each side plus the volume of the corners - the slight non-90o corners makes little difference in the amount of concrete that has to be ordered.

For the slab on top, its volume is the area of the trapezium times the depth of the slab (all in the same units):

volume_slab = (12 x sum_of_parallel_sides x perpendicular_distance_between_those_parallel_sides) x depth_of_slab

If you have trapezium shaped footings, then I guess you have a footing with a trapezium cross-section: use the volume_slab formula above with appropriate choices for the parallel sides (of the trapezium) and the depth_of_slab would be the length_of_footing.