ABSTRACT
TESTING The dynamic behaviour of the building, subject to ambient (wind) excitation, was measured during June 1990 to determine its natural frequencies, mode shapes and damping values. This is somewhat analagous to a doctor listening to a patient's heartbeat with a stethoscope - the natural frequency being the "heartbeat" and accelerometers being the "stethoscope". The theory of structural dynamic behaviour is summarised in Reference 1 and is not repeated here for brevity. The testing set up is shown in Figure 3 - major equipment used comprised four servo-accelercmeters, a four-channel analogue tape recorder and a two-channel spectrum analyser. A deliberately small arrangement (number of measurement locations) was chosen to determine whether a rapid, lew cost test could in fact determine the dominant structural characteristics. With a four-channel recorder this necessitated recording two sets of data (test series A and B as shown in Figure 3) on the ninth floor (top floor). Recorded data was visually monitored using an oscilliscqpe/chart recorder concurrent with the tape recording. Data processing was carried out "off-line" in Lloyd's Register Laboratories immediately following the tests. Each test series lasted two hours, to minimise random and bias errors and to ensure stationary wind measurements (see Reference 2).
