Identification of distributed material properties using measured modal data

Beams, made in brittle materials like concrete or cement, show increasing crack development during their service life due to mechanical and environmental loadings. This local damage can often be translated into reduction of the local bending stiffness values. This paper presents a scanning method to identify the local stiffness values of thin beams using experimentally measured resonance frequencies and their associated mode shapes. A measured modal displacement field is scanned by a special purpose finite beam element. Unlike traditional finite beam elements, each nodal point has the transversal beam deflection as the only degree of freedom (no rotational degrees of freedom). This sole degree of freedom can be compared directly with the measured transversal deflections of mode shapes by a laser Doppler scanner. The performance of the scanning method is first tested on simulated finite element and experimental data.