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Dynamic characteristics of a 30 storey building during construction detected from ambient vibration measurements Schuster, Norman David


The dynamic response of building structures to earthquakes has become an issue in the province of British Columbia because of increased awareness of the seismic hazard in this region. While there is a great deal of knowledge about structural dynamics, the majority of this knowledge is based on uniform structures. Hence, there is concern about extrapolating these results to the behaviour of nonuniform building which emerge from current architectural trends. The focus of this study was to monitor and to quantify the dynamic characteristics of a 30 storey, reinforced concrete building during its construction. This building is representative of the type of construction in Vancouver, B .C. and is therefore a useful case study. In addition, the lateral force resisting system in this structure is uniform in plan and elevation while the distribution of storey mass is asymmetrical due to its geometry as well as a major setback at one corner. Dynamic characteristics were determined by analyzing ambient vibrations of the structure. These vibrations were acquired and processed using a testing system developed at the University of British Columbia (Department of Civil Engineering). Several computer programs were developed during this project to complement the existing software. The objectives of this study included determining mode shapes and periods, determining the effect of architectural components, assessing base motion, and assessing the manner of the core’s deformation. In addition, a dynamic analysis was performed to assess the accuracy of modeling techniques. Finally, some aspects of current building codes were assessed. Ambient vibration testing methods proved very practical and useful. Torsional motion and modal coupling were found to be very significant, while little motion was detected at the base of this building. Natural frequencies decreased and tended to converge as the building height increased. Architectural components did not significantly influence the dynamic characteristics. The dynamic behaviour of this building could be accurately represented using dynamic analysis. Finally, the building code provisions considered in this study appear to be appropriate.

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