Technical Paper January 1, 2014.
Flexural concrete walls (i.e., walls the yield in flexural prior to failure) are used commonly as the lateral load resisting system for mid‐ and high‐rise buildings on the West Coast. They are relatively stiff under service‐level loading, can take on various configurations to accommodate architectural constraints, and are generally assumed to exhibit ductile response under severe earthquake loading. Despite heavy reliance on concrete walls, relatively little research has been done to investigate the earthquake performance of walls with modern design details. Few data exist characterizing the performance of modern walls under variable levels of earthquake loading or the impact of various design parameters on this performance. Few data exist to support evaluation and validation of numerical models for modern walls.
In 2004 a research study funded by the National Science Foundation (NSF), through the Network for Earthquake Engineering Simulation Research (NEESR) program, was initiated to investigate the earthquake performance of slender modern walls. This study is being conducted primarily by faculty and graduate students at the Universities of Washington and Illinois, with experimental testing conducted using the NSF‐funded NEES laboratory at the University of Illinois, Urbana‐Champaign (UIUC). The objectives of this study are to generate experimental data characterizing the seismic response and performance of modern concrete walls, develop numerical models for simulating wall response to support design and research, and develop recommendations for performance‐based seismic design of these systems.
The NSF‐funded study included experimental testing of planar rectangular walls, a planar coupled wall, and a C‐shaped wall, with experimental testing limited to unidirectional lateral loading and constant axial loading. In 2009 the Charles Pankow Foundation (CPF) provided supplemental funding to expand the scope of this study to include investigation of the impact of bidirectional loading on the earthquake performance of isolated C‐shaped walls and C‐shaped walls in coupled core‐wall systems.
This document presents the results of the three C‐shaped wall tests conducted as part of the NSF and CPF funded study. All three specimens had nominally the same design. The specimens were designed to represent C‐shaped walls in a coupled core‐wall system in a modern mid‐rise building. Specifically, specimens represented the bottom three stories of a C‐shaped wall in a ten‐story core‐wall building; loads were applied to the top of the specimen to achieve a load pattern at the base of the specimen representative of that which would develop in the ten‐story building. All three specimens were subjected to quasi‐static cyclic lateral loading in combination with axial loading. The first specimen, identified as Wall 6 of the NSF‐CPF project, was subjected to unidirectional lateral loading in the direction of the web of the C‐shaped wall and a constant axial load. The second specimen, Wall 7, was subjected to a cruciform lateral load pattern (i.e. loading in the direction of the web of the wall followed by loading in the direction of the wall flanges) as well as bidirectional lateral loading and a constant axial load. The third specimen, Wall 8, was subjected to a cruciform lateral load pattern, bidirectional loading and varying axial load. For Wall 8, a constant axial load was applied when the wall was subject to lateral loading in the direction of the web of the wall; a varying axial load was applied when the wall was subjected to lateral loading in the direction of the wall flanges to simulate the variation in axial load resulting from coupling action in the core‐wall system.
The response of test specimens was monitored using multiple instrumentation systems. Multiple fixed and roaming still cameras were used to document damage. A close range photogrammetric system and 2 a Nikon metrology / Krypton system were used to generate displacement field data. Displacement transducers were used to measure specimen deformation and specimen displacement. External concrete strain gages and embedded steel strain gages were used to monitor local strains. Load cells were used to monitor applied loads. This report employs data from load cells and displacement transducers as well as still camera images to characterize wall behavior and provide a preliminary assessment of performance. In the future, data from other instrumentation systems will be employed to refine the preliminary characterization and performance assessment. All data will be archived and made available to the public via NEEShub (http://www.neeshub.org).
The presentation of the C‐shaped wall tests is organized as follows. Section 2 presents the specimen design and construction. Section 3 presents material data for the concrete and steel used in specimen construction. Section 4 presents the test setup and the loading protocol used for the tests. Section 5 presents the instrumentation systems and data collection protocol. Section 6, 7, and 8 presents results for the individual wall tests. Section 9 compares the observed behavior of the three specimens. Section 10 presents preliminary conclusions of the experimental investigation.
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NOTE: At the time of publication, the author Anahid Behrouzi was not yet affiliated with Cal Poly.