engleski

Modal identification of structures during static load testing: Interaction effects

Structures such as floors or bridges are usually tested, according to some standards, in order to check some of their properties. Stiffness and modal parameters can be obtained through static and dynamic testing. Usually, static testing consists in adding mass to the structure and measuring the additional deflection. For convenience reasons, the added mass is usually implemented with tanks of water. However, if the static testing scenario is used to conclude modal parameters or dynamic serviceability assessment, it is necessary to ensure that the added load is representative of the structure conditions during its life span. Although for static load testing the results do not depend on the nature of the gravitational load, the same does not occur when modal parameters are of interest. Whether the mass is solid (sandbags or concrete blocks), liquid (water in tanks) or other types (as vehicles or people, etc.) greatly affects the damping due to interaction phenomena. These interaction effects appeared in an attempt to evaluate the damping on a wooden floor through traditional techniques (modal analysis using a shaker and some accelerometers). With the floor without any load, the different modes of their girders (one-way slab floor) could be easily identified and their frequencies and damping ratios well quantified. However, when supporting water tanks, the identification procedure was a challenging task. Trying to understand how the nature (solid or liquid) of the added mass affects, six case studies based on a lab-scale structure are presented.

structural dynamics ; experimental modal analysis ; solid or liquid live loads

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