Local ductility of steel elements under near-field earthquake loading

• Near-field earthquakes are characterized by a predominately strain-rate effect.
• The wave propagation theory was introduced to explain the wave velocity and the strain-rate effect.
• By the analogy of the Newton’s cradle concept, an explication for brittle fractures was provided.
• The plastic collapse mechanism theory in association with strain-rate rules was used for the study of I-shaped beams.
• A parametrical analysis reveals as the main factors of influence the flange thickness, the local buckling wave and the yielding ratio.

The paper tackles the influence of the near-field earthquakes on the available deformational capacity of steel elements through a global view, joining the results of the wave propagation theory with the one of the local plastic mechanisms. Different from the case of far-field earthquakes, where the structural behavior is dominated by cyclic loading, for near-field earthquakes the structural response is characterized by pulse loading produced by the seismic wave propagation along the height of the structure. Due to this fact, the structure response is dominated by the effect of the strain rate, thus reducing the local ductility and increasing the danger of fracture. After a presentation of the propagation theory applied to near-field earthquakes, the effect of the strain rate on the rotation capacity and on the fractural rotation of the beam elements, considering the fabrication type (rolled or welded) and temperature (room and low) conditions, is studied. It was revealed that the controlled flange buckling, as well as, the yielding ratio is the decisive parameters in order to avoid brittle failures. Finally, a novel representation about the damage produced during the Northridge and Kobe earthquakes due to seismic wave propagation is provided.