Report No.: CCEER-96-3
Title: Seismic Retrofit of R/C Oblong Tapered Bridge Columns with Inadequate Bar Anchorage in Columns and Footings
Authors: I. Darwish, M. Saiidi, and D. Sanders
Date: May 1996
Sponsoring Agency: Nevada Department of Transportation
Department of Civil Engineering/258
University of Nevada, Reno
Reno, NV 89557
A large number of bridges located in the I-80/U.S.-395 Interchange and other similar bridges along I-80 in the Reno/Sparks area have been identified as having potentially inadequate detailing to resist earthquakes. A common deficiency in many columns of these bridges is short dowel bars in the footing and short lap splices at the base of the columns. Also, the columns are poorly confined and lack adequate shear strength. To study the effectiveness of retrofitting of deficient bridge columns, two as-built and four retrofitted 0.4-scale models were constructed and tested. This report presents the study of the retrofitted specimens. The as-built specimen tests are described in Ref. 9. Two of the retrofitted specimens represented the retrofitting of the specimens with a one-way hinge detail. One was tested with yielding anchor bolts, while the other was tested with a yielding base plate. The other two retrofitted specimens represented columns with a fixed base detail. One of these was tested in the strong direction of the column while the other was tested in the weak direction.
A steel jacket was placed on each of the retrofitted columns to improve the shear strength and the concrete confinement over the lap splices. To ensure moment transfer, these steel jackets were connected to the footings by a base plate and bolts which were anchored to the footing. These bolts were essential because the tests of the as-built specimens showed that column dowels in the footings were too short and did not maintain the column-footing integrity under cyclic loads. All specimens were subjected to a nominally constant axial load and cyclic lateral loads.
Results from testing the retrofitted specimens showed that connecting the steel jacket to the base plate provided an effective retrofitting method and enabled the columns to reach their design strength under cyclic lateral loading. This retrofit also enhanced the shear strength and ductility capacity of the columns. In addition to the experimental study, seismic design recommendations and design procedures were presented that can be used in the seismic retrofit design of the column-to-footing connections of Northern Nevada bridges (Abstract by authors).