Mode shape identification of an existing three-story flexible steel stairway as a continuous dynamic system

George D. Manolis, Triantafyllos K. Makarios, Vasiliki Terzi, Ioanna Karetsou

The issue of modal shape identification for a flexible steel stairway located within the building complex comprising the Civil Engineering department of Aristotle University in Thessaloniki, Greece is presented here. The aforementioned stairway is a system with continuous distribution of mass and stiffness, a fact that makes structural identification challenging as compared to structures where lumping of these two basic parameters can be observed. More specifically, this stairway was instrumented using a local multi-channel network of accelerometers. Two 12 bit-nominal resolution, digital uniaxial accelerometers of the type KUOWA-PCD-30A, connected by cables and with `common time' and `common start' characteristics were installed on the stairway. The dominant modes of vibration of the stairway were computed by the `modal response acceleration time history methodology'. In parallel, a detailed finite element method model of the stairway was constructed and calibrated according to the ambient vibration results. We note that the identification procedure used for the dynamic characteristics of spatial structures yields results that can be used to develop a family of numerical models for the stairway ranging from the simple single-degree-of-freedom system to highly detailed multiple-degree-of-freedom models. Finally, some useful information on the theoretical procedure for the identification of modal shapes is included~herein.