“Computational Civil Engineering - "Intersections" International Journal

226 C. C. Comisuflexibility, inertia and damping that govern the dynamic responses) with theexperimental components of research in step 7 (algorithm to quantify modalparameters).The experimental techniques can be further sub-divided into two categories - singleexciter techniques and multiple exciter techniques. This paper is focus to find analgorithm to quantify modal parameters obtained by the single exciter techniques.2. STRUCTURAL DYNAMICSConsider a simple free-free beam shown in figure 1, and assume it has onlythe first three degrees of freedom. To determine the total vibration of the beam, itmast be excited at some point and the vibration measured at several points on thebeam. If this time domain information were transformed to the frequency domain,the frequency response curves obtained at the three points would be as shown infigure 1. That the sharp peaks (resonances) occur at the same frequencies,independent of where they are measured on the beam; the only difference is therelative height of the resonances.FIRST MODE3SECOND MODE THIRD MODE2MEASUREMENT POINTS1FREQUENCYFIRST RESPONSFREQUENCY SECOND RESPONSFREQUENCYTHIRD RESPONSFREQUENCYVIBRATION EXCITERFig. 1. Frequency response of a free-free beam at three measurement points [2]