Behavior of rectangular concrete walls subjected to simulated seismic loading

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Aaleti, Sriram
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Sri Sritharan
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Civil, Construction, and Environmental Engineering

Structural walls are frequently used in buildings to resist earthquake lateral loads because of their effectiveness in limiting the building drifts and minimizing damage to both structural and non-structural elements. In a collaborative effort, as part of a PreNEESR project, three y -scale reinforced concrete rectangular shear walls were subjected to cyclic loading at the Multi-Axial Subassemblage Testing facility (MAST) at University of Minnesota. Also, a y-scale precast wall system was tested at National Center for Research on Earthquake Engineering (NCREE), Taiwan to validate PreWEC system concept.

Overall dimensions of all four rectangular walls were identical, except that four different approaches were used to anchor the wall into the foundation. In the first wall, RWN, the longitudinal reinforcement was anchored into the foundation with adequate anchorage length without using any splices, while the second and third walls used couplers and code-based conventional lap splices to connect the wall reinforcement with the starter bars placed in the foundation. The precast wall, referred as PreWEC-1, used unbonded post-tensioning to anchor the wall to the foundation. All three reinforced concrete walls had two different stiffness and strength in the two in-plane loading directions as they were modeled to represent the response of a T-shaped concrete wall tested as part of the same project. PreWEC-1 was designed to replicate the response of RWN in in-plane weaker direction.

The fiber-based nonlinear beam-column element available in OpenSees software was used to model all three reinforced concrete walls with adequate attention to capture the influence of different anchorage details. In addition to capturing the total global response, the accuracy of the analysis was also examined in terms of simulating the local response as well as various displacement components due to flexure, bond slip at the critical section resulting from strain penetration, and shear. A zero-length bond slip element was used to account for the strain penetration effects while a nonlinear spring element was used to account for the shear deformation. By comparing with the experimental results, it was found that the analytical models well simulated the force-displacement responses including the unloading and reloading stiffness. However, it was found that the pinching model available in OpenSEES, which has been used in the past to represent the shear deformation hysteresis, was not capable of capturing all the critical points in the shear deformation response recorded during testing. Hence, a monotonic and hysteretic cyclic shear model was proposed using the strut-and-tie modeling technique. The proposed cyclic shear model captured the observed experimental shear response adequately.

As part of PreWEC-1, testing an innovative, economical mild steel connector was developed and its behavior under cyclic shear loading was characterized using experimental and analytical means. The PreWEC system performed exceptionally well with good energy dissipation, self-centering ability and had 15% higher capacity compared to the traditional reinforced concrete wall. Simplified analytical and design methods were proposed to characterize the behavior and designing of PreWEC systems. The simplified analysis captured overall force-displacement response, connector displacements and wall contact length accurately.

Thu Jan 01 00:00:00 UTC 2009