In 1996, Chile adopted NCh433.Of96, which includes seismic design approaches similar to those used in ASCE 7-10 (2010) and a concrete code based on ACI 318-95 (1995). Since reinforced concrete buildings are the predominant form of construction in Chile for buildings over four stories, the 27 February 2010 earthquake provides an excellent opportunity to assess the performance of reinforced concrete buildings designed using modern codes similar to those used in the United States. A description of observed damage is provided and correlated with a number of factors, including relatively high levels of wall axial load, the lack of well-detailed wall boundaries, and the common usage of flanged walls. Based on a detailed assessment of these issues, potential updates to U.S. codes and recommendations are suggested related to design and detailing of special reinforced concrete shear walls.
Reinforced concrete buildings utilizing structural walls for lateral load resistance are the predominant form of construction in Chile for buildings over four stories. Typical buildings include a large number of walls, with ratios of wall cross-sectional area to floor plan area of roughly 3% in each principal direction. Based on the good performance of RC buildings in the March 1985 earthquake, requirements for closely spaced transverse reinforcement at wall boundaries were excluded when Chile adopted a new concrete code in 1996 based on ACI 318-95. In recent years, use of three-dimensional linear models along with modal response spectrum analysis has become common. Since 1985, nearly 10,000 new buildings have been permitted. Although the newer buildings have similar wall area to floor plan areas as older buildings, newer walls are thinner and buildings are taller, leading to significantly higher wall axial load ratios.
Reinforced concrete structural walls are commonly used to provide lateral strength and stiffness to resist lateral loads from wind or earthquake. Slender walls usually require large amounts of longitudinal reinforcement at wall boundaries to satisfy code lateral strength requirements; therefore, use of structural steel reinforced concrete (SRC) walls, where the boundary longitudinal reinforcement is replaced by a structural steel section, is a potentially attractive alternative. This study presents results of an experimental program involving tests under combined gravity and lateral loading for three, heavily instrumented, moderate-scale SRC slender walls. Primary test variables included varying the size of the embedded structural steel section and the quantity of transverse reinforcement provided at the wall boundaries. Although slip of the structural steel was observed for all specimens, test results reveal good behavior up to and beyond 2% lateral drift, even for a specimen with only modest confinement at the wall boundaries.
Previous earthquakes, such as the 2010 Maule earthquake in Chile, have demonstrated the need to establish suitable predictors of compressive or tensile strains in concrete or steel in reinforced concrete shear walls, which can provide limit states or confinement requirements. Slender walls are commonly controlled by flexural deformations that can be divided into elastic and inelastic components. This study provides calibrated expressions for the elastic and inelastic components of flexural deformations using a fiber model for slender walls. These expressions are obtained for rectangular and T-shaped walls. The elastic component is dependent on the axial load and the boundary steel reinforcement ratio. The impact of wall coupling is investigated, which requires a correction for the elastic component. The investigation of the inelastic component is based on a plastic hinge model, in which the length of the plastic hinge is a function of the lateral inelastic drift of the wall among other parameters. The traditional linear inelastic curvature distribution over the wall height is also modified for cases with steel reinforcement with a long yield plateau or low strain hardening, which results in a larger curvature at the wall base. The distribution is validated with experimental data from the literature.InnovaChile-Corfo
10CREC-8580
Chile's National Commission on Scientific and Technological Research (CONICYT)
113021
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