The paper firstly outlines typical differences between the philosophy of conducting modal testing in civil engineering compared to the application of the same technology in mechanical, automotive and aerospace engineering. These differences have a strong influence on the selection of a fast modal testing technique suitable for civil engineering applications. The instrumented hammer testing technique, where the impostor is a manually operated sledge hammer proved to be very popular because of its low cost, simplicity and speed of execution. However, specifics of modal testing of civil engineering structures such as the use of portable equipment in open space environments, low natural frequencies, closely spaced modes of vibration and relatively high damping require special consideration. This paper discusses some of these considerations which are not adequately addressed in the available literature. The problems presented are related to the use of a portable spectrum analyser, which typically has a limited number of digital data analysis options, when performing modal testing of long span concrete floors and footbridges using an instrumented sledge hammer.
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