Originally accessed:
Portland Cement Association
"Located in Seismic Zone 3, the structure is designed for a combination of gravity and lateral forces in accordance with the 1997 Uniform Building Code. Lateral resistance is provided by a combination of shearwalls and special moment-resisting frames (i.e., a dual system), with approximately 70 percent of the seismic forces carried by the shearwalls. This type of lateral-force-resisting system is both well balanced and highly redundant, providing the necessary strength and ductility required for the prescribed level of seismic risk. The shearwalls, which are 24 in. (610 mm) thick for the full height of the building, are located around the elevator and stair cores. At the top of the parking structure (8th floor), the lengths of the walls are reduced to account for the decrease in lateral forces."