Existing steel frames not complying with modern seismic codes are often vulnerable to earthquakes due to inadequate seismic detailing. These types of framed structures typically feature semi-rigid and partial strength column-base connections; the behaviour of such connections may significantly affect their seismic performance. However, current code provisions offer limited guidance for the assessment and retrofit of column-base connections To fill the knowledge gap, the H2020 EU-funded Earthquake Assessment of Base-Column Connections in Existing Steel Frames project experimentally investigated, the response of exposed column-base plate connections. Bi-directional Pseudo-Dynamic tests were carried out at the Structures Laboratory of the University of Patras within the framework of "Engineering Research Infrastructures for European Synergies - ERIES" project. The case-study steel frame featured two types of column-base plate connections, i.e., stiffened and unstiffened, representing respectively the base connections of an external moment-resisting frame and an internal gravity frame. The experimental programme comprised free vibration tests to identify the modal properties of the sample steel frame. A set of quasi-static cyclic tests and pseudo-dynamic tests were then carried out to investigate the performance of the steel frame under bi-directional earthquake sequences. The response of each component constituting the column-base plate connections was monitored during the tests to fully capture the behaviour of the connections. Such experimental results allow model calibration and further parametric investigation on column base plate connections.
Keywords: Column-base steel connections; biaxial testing; pseudodynamic method; steel frame connections; sub-standardard buildings.
The international building stock comprises structures built decades ago, on the basis of past knowledge and before the advent of modern seismic codes. Some critical connections of such steel structures (e.g. the plates welded at the bottom of columns to secure their connection to the foundation) may be particularly vulnerable to earthquakes, especially when they strike the structure concurrently from two transverse directions: the plates may deflect and uplift, accumulating deformations which may endanger their integrity. Since earthquakes do not occur only once in the life span of a structure, these structural parts are subjected to cumulative damage placing under question their capacity to sustain future earthquakes. Under support provided by the European Commission, the project aims at studying this phenomenon by constructing and testing in a specialized European research laboratory a steel building - representative of this class of structures - at full scale. Employing an innovative experimental technique to impose repetitive biaxial seismic excitation on the specimen and through a large number of sensors, valuable data for the local and global response of the frame was possible. The data are made openly available for re-use by the scientific and professional engineering community.
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