Seismic Retrofit of Octagonal Columns with Pedestal and One-Way Hinge at Base: Discussion.

Recent earthquake experience has shown that the response of retrofitted bridges is generally satisfactory. However, many seismically-deficient bridges remain, notably those that are supported on piers that lack proper detailing to resist strong earthquakes. This brief discussion article comments on a recent study of seismic retrofit of bridge columns (Johnson et al, 2005). The original study used columns that are irregular both in the cross section and along the height, with the latter caused by the presence of a pedestal and a one-way hinge connection between the footing and the pedestal. The columns were subjected to a simulation of the 1994 Northridge Sylmar earthquake in the strong direction until failure. Results showed that the pedestal retrofit was successful in strengthening the pedestal sufficiently to shift the plastic hinging into the column. Johnson et al suggest that bond slip, shear deformation, and strain rate effects be accounted for in any effort to obtain a reasonable estimate of the push-over response of piers. Solanki's response addresses five topics: the hinges at the base of the columns; horizontal thrust (shear) and rotation of the hinges; other types of horizontal confinement that could have been used; hinge design and its impact on the cracking and peeling of the concrete cover over the transverse reinforcement; and how the retrofit condition for the structural members occurred. The original authors made a brief closure, which is appended to this discussion.