| Summary: | The Ministry of Transportation and Highways of British Columbia has conducted a
seismic assessment and upgrade initiative for many of its major bridges. Many deficiencies
had been noted in the reinforced concrete approach bents of these bridges and the
consequences of recent failures caused by earthquake loading have emphasized the need for
retrofitting to be carried out on bridges with deficiencies.
Since the costs of rehabilitating the bridge bents are significant, a scale model testing
program was devised. Models of bents comprising the details of the approach spans of the
Oak Street Bridge were cast and then subjected to slow cyclic lateral load testing. The
specimens were instrumented externally with linear potentiometers, and internally using strain
gauges bonded to the reinforcement.
The objectives of the test program were primarily to confirm the seismic deficiencies in
the as-built bents and to prove the adequacy of proposed economical retrofit schemes for twocolumn
bridge bents. Particular to this thesis, the test program was also intended to produce
data for further research that would contribute to the art of retrofit design. The strain gauge
data obtained from the test program presented the opportunity to derive section curvatures at
discrete locations wifJiin the specimens for various stages of loading.
The data obtained from the strain gauges of the models were analyzed. Curvature
distributions for two of the retrofit schemes that performed particularly well were derived.
The distributions were integrated to give deflections which were then compared with the
measured displacements. The errors in the calculated displacements ranged from -3% to
+21%.Using the theoretical member properties, combined with the known material
properties, analytical curvature distributions were derived using the non-linear analysis
program DRAIN-2DX. The shapes of the distributions and the peak curvature values were
the focus of interest and using moment-curvature relationships, estimates of peak concrete
strains were predicted and compared with peak strain capacities. The strain capacities were
derived from theory that accounts for the level of confinement provided by transverse
reinforcement in a section. It was estimated that the architectural fillet region of the beamcolumn
joint region, when in compression, was able to provide confinement enough to sustain
concrete strains of the order of 0.013. The same fillet region retrofitted with high strength
fiberglass wraps was estimated to be capable of ultimate concrete strains of approximately
0.027.
The experimentally derived curvatures were then compared with those obtained
analytically. It was found that the curvature distributions and the peak values compared
reasonably well, which increased the confidence in the ability of the analysis to predict the
flexural behaviour of retrofitted two-column bridge bents. The inclusion of joint shear
deformations reduced the curvature demand in the plastic hinge regions and improved the
agreement between the experimental and analytical curvatures.
It is felt that the deterioration of the bond between the concrete and the reinforcement,
caused by the cyclic nature of the tests, facilitated the derivation of reasonable approximations
to the curvature distributions by reducing the tension stiffening effect on the reinforcement.
This deterioration of the bond, particularly in the plastic hinge regions, decreased the
variations of experimental curvatures occurring between cracks. === Applied Science, Faculty of === Civil Engineering, Department of === Graduate
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