An Estimate of the Yield Displacement of Coupled Walls for Seismic Design

A formula to estimate the yield displacement observed in the pushover analysis of coupled wall lateral force-resisting systems is presented. The estimate is based on the results of an analytical study of coupled walls ranging from 8 to 20 stories in height, with varied amounts of reinforcement in the reinforced concrete coupling beams and walls, subjected to first-mode pushover analysis. An example illustrates the application of these estimates to the performance-based seismic design of coupled walls

flexibility

Empirical observations and analysis of the recorded response of two California bridges indicate that the flexibility of the bridge embankments has a significant effect on the displacement demands sustained by the columns of short bridges under seismic excitation. Because the deck and abutments provide a capable load path, the columns only need to maintain gravity load support while accommodating the lateral displacement demands associated with the response of the embankments. This is in contrast to conventional R (or Z) factor approaches, which require the columns to provide substantial lateral resistance and, hence, lead to relatively large diameter columns that have limited displacement capacity. A displacement-based approach to the design of the columns is proposed. Displacement demand is assessed for one or multiple performance objectives using a simple extension of the "N2" model to address the nonlinear response of the embankments. Relative to conventional designs, the smaller diameter columns obtained with this approach have better seismic performance. The columns have a larger displacement capacity and sustain less damage because they have larger yield displacements. The columns also are much less vulnerable to shear failures because of their more slender aspect ratios. Normalized embankment capacity curves are provided, and their use is illustrated with an example.C1 Pamukkale Univ, Dept Civil Engn, Denizli, Turkey.Santa Clara Univ, Santa Clara, CA 95053 USA

estimates and experimental results

The transition to displacement-controlled methods for seismic design relies on explicit measures of deformation capacity. Although conceptually clearly defined, the various alternative indices such as displacement ductility, drift and plastic rotation capacity calculated with the available analytical tools in the literature are marked by excessive scatter when tested with well-controlled experimental results, indicating that the validity of the underlying physical models is questionable. This problem is explored systematically in the current paper, by evaluating the parametric performance of the analytical models, as well as through comparison with the experimental trends. An important result of the present study is that well- confined members designed as per the ATC-32 requirements have large dependable deformation capacities regardless of the axial load ratio, a finding with significant implications in practical bridge seismic design