Vertical Ground Motions and Its Effect on Engineering Structures: a State-of-the-art Review

During the recent earthquakes, the vertical component of the ground motion found to be exceeding the horizontal component, which directly contradicts the current codal provision that assumes the value of the vertical ground motion to be 1/2 to 2/3 of the horizontal component. Almost after every destructive earthquake engineers postulates that the structural damage such as elephant foot buckling of large column, fracture of large diameter reinforced concrete column supporting building and freeway structures was due to strong vertical ground motion. Therefore, seismic design of the structure without the consideration of the vertical ground motion component may result in unquantifiable risk from the collapse, especially those constructed in the close proximity of the fault. However there seems to be no consensus as to the importance on damage due to vertical motions, and little that has been learned from the recent earthquake in Loma-Prieta, Northridge, or Kobe which indicates conclusively that damage to structures was predominantly by vertical motions. This paper presents the assemblage of the state-of-the-art study on the vertical ground motion and its effects on the engineering structures.