Cyclic Testing of Large-Scale Rectangular Bridge Columns under Bidirectional Earthquake Components

Bidirectional cyclic testing was performed on four half-scale reinforced-concrete rectangular bridge column specimens to examine the need to account for bidirectional seismic loading in design for earthquakes expected in eastern and western regions of North America. The prototype structures are common two-span, skewed bridge structures designed according to the seismic provisions of Canadian Standards Association (CSA)-S6-06. The column specimens are $1.2\times 0.6\mathrm{m}$ in cross section and 3.0 m tall and assumed to carry a gravity load of 6% $A_g{f}_c^{\prime }$. Two specimens were designed for Montreal, Quebec, Canada (east site), using 0 and 30% combination rules, resulting in longitudinal steel ratios of 0.41 and 0.57%. Two specimens represented the column part of bridges located in Vancouver, British Columbia, Canada (west site), with longitudinal steel ratios of 0.97 and 1.72% resulting from the application of 0 and 40% combination rules. Site-specific cyclic displacement test protocols were developed from time-history analysis of the bridges. For both sites, the tests showed that the combination rules used in design had no significant influence on the inelastic cyclic response of the columns. The columns designed for the Montreal site exhibited satisfactory inelastic cyclic performance even if they had a longitudinal reinforcement ratio less than the current CSA S6 limit of 0.8%. All columns were subjected to biaxial shear forces corresponding to their biaxial flexural strength envelope. For all specimens, the height of the plastic hinge region was approximately equal to the smaller column dimension, rather than the larger one as currently specified in CSA S6.