Experimental testing of RC walls using extensive instrumentation to investigate cyclical nonlinear wall behavior
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A series of experiments on large reinforced concrete structural walls are being conducted in the University of Illinois Network for Earthquake Engineering Simulation (NEES) facility. The types of walls being tested include planar, coupled, and C-shaped walls. Most of these walls are approximately one-third scale, 4 m high, and model the bottom three stories of a high-rise building. Two versatile six degree-of-freedom loading units are being used at the top of each tested wall segment to apply the axial compression, shear, and overturning moment that would be expected at the third story level of a 10 story prototype building. An additional special feature of this research program is that advanced non-contact measurement systems are being used to make dense and accurate measurements of displacement fields and developing damage. A set of high-resolution pre-calibrated cameras are used to record damage on the surface of the test structure over the entire loading history. The overall objective of this project is the development of improved performance-based design methods for structural walls. This presentation will focus on two important aspects of the measured response of already tested wall structures, those being the compressive response of boundary regions and the tensile response of cracked structural concrete. In both of these cases, the extensive data collected by the coordinate measurement machine and high-resolution cameras provided what is considered to be an unprecedented level of information for understanding the response of these walls. For the compressive response, these measurements were used to assess the influence of amount of longitudinal and confinement reinforcement, stress level, and cycle number on the limit states of localized crushing, full engagement of confinement reinforcement, wall bulging, bar buckling, distributed crushing, and structural instability. For the tensile response, these measurements were used to similarly assess the influence of structural reinforcement detailing on the development of cracking (spacings and widths), bond degradation, tension stiffening, dimensions of yielding zone, and rupture of bars in pure tension. In both the examination of the compressive and tension responses, a detailed comparison was made between the measured responses of the test specimens and the responses that were predicted by non-linear finite element analysis. These comparisons were used to examine the limitations of existing models for strength degradation and how best to apply these models and revisions to these models to make reliable predictions of the response of structural concrete walls. Due to limitations in length, this paper presents only selected results.
