Modificación de los modos de vibración de dos edificaciones aporticadas de hormigón armado con irregularidad en planta para reducir la respuesta torsional

Abstract

Torsional response in reinforced-concrete moment-resisting frame buildings with Type 1 plan irregularity is associated with eccentricities between the center of mass and the center of rigidity, which increases drifts in perimeter frames and rotations under seismic loading—an effect that can be observed in the system’s vibration modes. This research aims to modify the fundamental vibration modes of two reinforced-concrete frame structures with Type 1 plan irregularity in order to improve their structural behavior under seismic actions by means of an optimization algorithm based on modal analysis. The hypothesis is that a localized redistribution of stiffness in the seismic-force-resisting system, aimed at reducing static eccentricity, decreases torsional response and promotes dominant translational modes, while also improving the efficiency of structural sizing. To this end, two buildings were modeled and their initial dynamic behavior was characterized through modal analysis. Subsequently, an optimization procedure was implemented to locally adjust the stiffness of vertical elements, using Particle Swarm Optimization (PSO) and evaluating structural parameters in accordance with applicable code-based criteria. As a result, reductions in static eccentricity and torsion-related indicators were achieved, together with changes in modal participation, with translational effective modal mass predominating in the main modes, demonstrating improved overall response to seismic loading compared with the original models. In conclusion, modal-analysis-based optimization makes it possible to control torsional effects through the strategic stiffening of vertical elements and, consequently, the adjustment of dominant modes, contributing to a more favorable seismic response without requiring generalized increases in member sizes, making it a useful alternative for tuning dynamic behavior at the design or assessment stage. Keywords: seismic torsion; modal analysis; eccentricity; Particle Swarm Optimization (PSO); plan irregularity.