Application of Nonlinear dynamics analysis to damage detection and health monitoring of highway structures

This describes a research program to apply nonlinear analysis and chaos theory to structural health monitoring. Earlier approaches based on linear modal analysis typically examined fundamental frequencies of the structure. However, significant changes in the fundamental frequency were usually not detected until the structure was severely damaged. In chaos theory, the fundamental frequencies are not assumed to be fixed, instead they wander in time in a characteristic pattern around a central value, called an attractor. In a chaotic system, a set of parameters called Lyapunov exponents play the role of fundamental frequencies in linear system analysis. The current FHWA research program involves the development of algorithms to extract these exponents from structural monitoring data. These algorithms are being evaluated against simulated data sets produced by an advanced 3-D nonlinear dynamics finite element code (LS-DYNA) using synthesized ambient traffic loadings, Chaotic behavior was observed in the modeled bridge.