RAM Concept calculates the footfall response of structures using assumed dynamic loadings that were derived from a large number of experimentally measured footfall force time histories. These studies also showed that normal walking rates range from about 1.5 to 2.5 steps per second.

The first four harmonics of the specified range of walking frequencies are considered. From these harmonics, a set of critical walking frequencies are determined that would coincide with the natural frequencies of the structure and thus promote resonance. The response must be calculated for each of these critical walking frequencies as it is otherwise not possible to determine which frequency is most critical.

The assumed periodic footfall function can be separated into any number of harmonic components using a Fourier series. RAM Concept uses four harmonic components in this evaluation.

where

W	=	weight of the individual walking
κ	=	dynamic load factor (refer to "A Design Guide for Footfall Induced Vibration of Structures" for a detailed discussion)
j	=	harmonic number
n	=	total number of harmonic components considered
T	=	period of the footfall

This relationship is demonstrated graphically below for a walking frequency of 1.5 Hz:

In the resonant analysis, a maximum natural frequency to use in the analysis can be input into RAM Concept . Only modes of vibration with natural frequencies less than or equal to the input value will be used in the resonant response analysis.