Evaluación y ajuste del factor de reducción de fuerzas sísmicas para estructuras de ductilidad limitada (mampostería confinada limitada a 2 pisos).

Abstract

The Seismic Force Reduction Factor, known as Factor R, is an essential parameter in seismic-resistant design as it converts elastic forces into applied inelastic forces, facilitating the design in the inelastic spectrum of the structure. This research analyzes Factor R for confined masonry buildings of up to two stories, a structural system with limited ductility and, therefore, a restricted capacity to dissipate energy without collapsing. The Ecuadorian Construction Code (NEC) assigns a value of 𝑅=3 for these structures, while international codes such as NSR-10 (Colombia), ASCE 7 (USA), Eurocode 8 (Europe), NTC (Mexico), and NCH433 (Chile) assign values ranging from 1.5 to 4 for similar systems. This suggests that the local value may be conservative and may not accurately reflect the actual behavior of buildings during seismic events. The methodology implemented uses expressions proposed by Dr. Roberto Aguiar to calculate Factor R based on the vibration period of the structure. These expressions consider three fundamental components: Ductility (𝑅𝑢), Overstrength (𝑅Ω), and Redundancy (𝑅𝑟). Using a representative structural model of confined masonry and the ETABS finite element program, the behavior of a two-story structure was evaluated through the Wide Column modeling method. The results confirmed the applicability of the proposed expressions and identified adjustments needed to enhance the safety and efficiency of seismic-resistant designs in high-seismic-risk zones. The results obtained demonstrate that the values proposed by the NEC can be reassessed, considering the characteristics of the analyzed structures, and offer a more precise framework for designing confined masonry buildings in seismic contexts.