UCLA

Experimental and analytical investigations were conducted to provide insight into the nonlinear cyclic response of moderate aspect ratio reinforced concrete structural walls. Five large-scale cantilever structural wall specimens, subjected to combined constant axial load and reversed cyclic lateral loading, were designed, constructed, instrumented, and tested. The wall specimens were designed to yield in flexure prior to loss of lateral load capacity. Primary test variables included aspect ratio (1.5 and 2.0), axial load level (0.025Agf'c and 0.10Agf'c), and wall shear stress level.

Test results showed that substantial loss of lateral load capacity was observed for a variety of reasons, such as diagonal tension, diagonal compression, sliding shear, concrete crushing, and buckling of vertical reinforcement. Test results also indicated that significant strength loss was impacted by wall aspect ratio, axial load level, and wall shear stress level. Although various failure modes were observed for five wall specimens, drift ratio at substantial loss of lateral load capacity was approximately 3.0% for all tests. The average contribution of nonlinear shear deformations to the top lateral displacement varied between approximately 20 and 50%, with lower values for the aspect ratio 2.0 walls.

Modeling parameters recommended by ASCE 41-06 and FEMA 356, including effective flexural and shear stiffness values, deformation capacities, and residual strengths, are compared with the corresponding values derived from test results. Current modeling approaches, including both uncoupled (P-M and V independent) and coupled (interaction between P-M and V) models, were used to assess their ability to capture the measured responses for the moderate aspect ratio structural walls. The investigation indicates that both models overestimate lateral load capacity and lateral stiffness, but with notable differences. In general, results for the uncoupled models are less consistent with the test results, indicating that coupled models are needed to adequately capture the responses of moderate aspect ratio walls. The primary shortcoming of the coupled model was the lack of cyclic material models. The detailed response information obtained from the heavily instrumented walls tested in this study provide essential data to develop robust analytical models, including models that account for cyclic nonlinear shear-flexure interaction.