Real-Time System Identification of a Nonlinear Four-Story Steel Frame Structure-Application to Structural Health Monitoring

Structural health monitoring (SHM) is a means of identifying damage from structural response to environmental loads. Real-time SHM is of particular use for rapid assessment of structural safety by owners and civil defense authorities. This paper presents an algorithm for real-time SHM during earthquake events using only acceleration measurements and infrequently measured displacement motivated by global positioning system. The algorithm identifies a nonlinear baseline model including hysteretic dynamics and permanent deformation using convex integral-based fitting methods and piecewise linear least squares fitting. The methodology identifies pre and postyield stiffness, elastic and plastic components of displacement, and final residual displacement. It thus identifies key measures of damage affecting the immediate safety or use of the structure and the long-term cost of repair and retrofit. The algorithm is tested with simulated response data using the El-Centro earthquake record and with measured response data. Both data sets are based on a four-story nonlinear steel frame structure using the El-Centro ground motion record. Overall, the algorithm is shown to provide accurate indications of the existence, location, and magnitude of structural damage for nonlinear shear-type buildings. Additionally, the identified permanent displacement is a particularly useful damage measure for the construction of probabilistic fragility functions.