To secure the integrity of welded steel structures, The Monitoring system to detect the infinitesimal fatigue crack, and the Crack growth simulation to estimate the fatigue life are effective. In present paper shows measuring method on initiation and propagation of fatigue crack by monitoring system, and measured results on bead-on-plate Welded specimen. And also, numerical simulations by"FLARP" are performed to verify the validity of numerical methodology. It is confirmed that crack initiation life and propagation rate estimated by FLARP agree well with experimental results.
