Damage Testing Of Civil Engineering Structures by Vibration Monitoring

Abstract

In seismic design, partial-strength composite steel-concrete moment resisting (MR) frame structures represent an open research field, both from a theoretical and an experimental standpoint. This paper presents the first results of vibration experiments, carried out with the scope of identifying changes in the dynamic response of a MR frame structure, following to the application of pseudo-dynamic (PsD) loadings. The specimen has been constructed and tested at the European Laboratory for Structural Assessment (ELSA) of the Joint Research Centre (JRC) in Ispra, and consists of a full-scale two-storeys two-bays frame presenting 12.8 m by 7.4 m dimensions in plan and 7.0 m in height. Resistance to lateral seismic loads is provided by three parallel MR frames in the main direction and by a bracing system in the orthogonal direction. Frames are made of composite beams and partially encased composite columns, connected by an innovative partial strength joint, and have been designed according to Eurocode 8 (EC8) rules. The testing program includes a sequence of PsD tests, simulating earthquakes with peak ground acceleration (pga) scaled up to the collapse limit state, followed by a final cyclic test. A dynamic characterization of the structure has been carried out before damaging the structure; it has been repeated after performing the ultimate limit state PsD test; and it has again been repeated after the PsD test at the collapse limit state and the final cyclic test. During each testing phase, the structure has been instrumented in three different configurations: the first one aimed at capturing the overall response of the building, while the other two focused on the characteristics of an interior and an exterior beam-to-column joints. Each characterization phase included shock tests, performed using an instrumented sledge-hammer, and stepped-sine tests, executed by means of an electromagnetic.

Data processing allowed the dynamic characterization of the overall structure from a global viewpoint to be performed and the variation of modal frequencies and damping ratio to be estimated.