A rapid decision making process of retrofit scheme for seismically-vulnerable reinforced concrete school buildings using simple information

Abstract

Many existing school buildings in South Korea constructed before application of seismic design code have seismically-deficient details. The inadequate details on the columns significantly affect the failure modes and the lateral resisting capacities of the entire structure. This paper aims to propose the rapid decision making process of the retrofit scheme with a previously-developed machine-learning model classifying the column failure modes for a typical seismically-vulnerable reinforced concrete school building. The retrofit scheme was established considering the failure mode, confinement ratio and stiffness ratio of the columns. The proposed process is as follows: (1) removal of the infilled walls mitigating a short column effect; (2) classification of the column failure modes for the first story column; (3) increases in the confinement-related parameters until the flexure failure occurs; and (4) increases in the stiffness-related parameters before the shear failure occurs. Based on the process, the retrofit schemes (removed wall, removed wall with 3.09 of stiffness ratio, removed wall with 0.07 of confinement ratio & removed wall with 0.15 of confinement ratio) were derived, and the seismic responses of the retrofitted models were compared to those of the as-built condition to investigate the effectiveness of the retrofit system. In conclusions, the removed wall with 0.07 of CR (stiffness ratio=5.29 & confinement ratio=0.07) was the efficient retrofit details for 2 %/50 y earthquake records. © 2025 Institution of Structural Engineers