The equivalent static design procedure described above is widely used in the petrochemical industry. Occasionally, the results of a equivalent static design results in a foundation which is impractical or too costly. In this situation, the dynamic analysis method can be used. A dynamic ananlysis takes into account the interia of the foundation mass in resisting, the load, and will generally yield a more eccomical design. The procedure is described in detail in TM5-856 (volumn4) and TR 4921.