Floor mounting chairs is the most common method of securing them to the building. Even chairs on risers are often mounted to the treads and not the riser face. Inclined floors are accommodated with the chair's mounting feet angled to match the incline of the floor. Requirements for mounting to concrete floors are shown here:
Irwin Seating can (and has) mounted chairs to other substrates like wood, steel and aluminum, and you should discuss your options with your Irwin Seating representative when using an alternative material.