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ArayaLetelier, G., Parra, P. F., LopezGarcia, D., GarciaValdes, A., Candia, G., & Lagos, R. (2019). Collapse risk assessment of a Chilean dual wallframe reinforced concrete office building. Eng. Struct., 183, 770–779.
Abstract: Several codeconforming reinforced concrete buildings were severely damaged during the 2010 moment magnitude (Mw) 8.8 Chile earthquake, raising concerns about their real collapse margin. Although critical updates were introduced into the Chilean design codes after 2010, guidelines for collapse risk assessment of Chilean buildings remain insufficient. This study evaluates the collapse potential of a typical dual system (shear walls and moment frames) office building in Santiago. Collapse fragility functions were obtained through incremental dynamic analyses using a stateoftheart finite element model of the building. Sitespecific seismic hazard curves were developed, which explicitly incorporated epistemic uncertainty, and combined with the collapse fragility functions to estimate the mean annual frequency of collapse (lambda(c)) values and probabilities of collapse in 50years (Pc(50)). Computed values of lambda(c) and Pc(50) were on the order of 10(5)10(4), and 0.10.7%, respectively, consistent with similar studies developed for buildings in the US. The results also showed that the deaggregation of lambda(c) was controlled by small to medium earthquake intensities and that different models of the collapse fragility functions and hazard curves had a nonnegligible effect on lambda(c) and Pc(50), and thus, propagation of uncertainty in risk assessment problems must be adequately taken into account.

Cando, M. A., Hube, M. A., Parra, P. F., & Arteta, C. A. (2020). Effect of stiffness on the seismic performance of code conforming reinforced concrete shear wall buildings. Eng. Struct., 219, 14 pp.
Abstract: This study assesses the effect of the stiffness on the seismic performance of residential shear wall buildings designed according to current Chilean regulations, including DS60 and DS61. Specifically, the paper focuses on the effect of stiffness on the building overstrength, displacement ductility, fragility for Life Safety (LS) and collapse limit states, as well as the probability of achieving these two limits states in 50 years. The seismic performance is assessed for a group of four 20 story residential shear wall buildings archetypes located in Santiago. Walls were modeled using the multiple vertical line element model (MVLEM) with inelastic hysteretic materials for the vertical elements, and a linear elastic shear behavior. Pushover analyses were considered to estimate the buildings overstrength and displacement ductility, while incremental dynamic analyses were per formed to estimate fragility curves. A probabilistic seismic hazard analysis, which considered the seismicity of Chile central zone, was performed to estimate the probability of achieving the two limits states in 50 years. The results show that an increase in the stiffness reduces the chance of exceeding the LS and collapse limit states for the same intensity level. Additionally, the probabilistic seismic hazard analysis shows that, when the stiffness increases, the probability of reaching the LS limit state in 50 years also decreases. Counterintuitively, the probability of collapse in 50 years increases as the stiffness increases, due to the considered seismic hazard and the design requirements. Since society is moving towards resilient structural designs that minimize damage, disruption and economic losses, it is concluded that the performance of reinforced concrete shear wall buildings is improved by increasing the stiffness.
Keywords: Reinforced concrete; Shear wall; Building; Collapse; Life safety; Stiffness; Fragility; Risk

Parra, P. F., Arteta, C. A., & Moehle, J. P. (2019). Modeling criteria of older nonductile concrete framewall buildings. Bull. Earthq. Eng., 17(12), 6591–6620.
Abstract: The purpose of seismic provisions included in modern building codes is to obtain a satisfactory structural performance of buildings during earthquakes. However, in the United States and elsewhere, there are large inventories of buildings designed and constructed several decades ago, under outdated building codes. Some of these buildings are classified as nonductile buildings. Currently, under the ATC78 project, a methodology is being developed to identify seismically hazardous framewall buildings through a simple procedure that does not require full nonlinear analyses by the responsible engineer. This methodology requires the determination of the controlling plastic collapse mechanism, the base shear strength, and the ratio between the story drift ratio and the roof drift ratio, called parameter alpha, at collapse level. The procedure is calibrated with fully inelastic nonlinear analyses of archetype buildings. In this paper we first introduce an efficient scheme for modeling framewall buildings using the software OpenSees. Later, the plastic collapse mechanism, the base shear strength, and values of alpha are estimated from nonlinear static and dynamic analyses considering a large suite of groundmotion records that represent increasing hazard levels. The analytical experiment included several framewall combinations in 4 and 8story buildings, intended to represent a broad range of conditions that can be found in actual buildings, where the simplified methodology to evaluate the risk of collapse can be applicable. Analysis results indicate that even walls of modest length may positively modify the collapse mechanism of nonductile bare frames preventing soft story failures.
