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ISSN : 1226-525X(Print)
ISSN : 2234-1099(Online)
Journal of the Earthquake Engineering Society of Korea Vol.30 No.1 pp.29-37
DOI : https://doi.org/10.5000/EESK.2026.30.1.029

Verification of Orthogonal Combination Rule for Nonlinear Static Analysis

Choi sori1), Hong Yoonsu2), Yu Eunjong3)*
1)Graduate Student, Department of Architectural Engineering, Hanyang University, 2)Post-doctoral Researcher, Department of Architectural Engineering, Hanyang University, 3)Professor, Department of Architectural Engineering, Hanyang University

Abstract

To ensure structural safety, seismic performance must be evaluated under ground motions applied in the principal direction that produces the maximum seismic response. However, in irregular buildings, additional torsional behavior may cause this principal direction to deviate from the analysis axes. Determining the principal direction requires identifying the orientation that yields the maximum base shear among all possible directions, which makes the procedure highly cumbersome. In practice, the 100:30 combination rule specified in current seismic design provisions is commonly used to evaluate seismic responses while conservatively accounting for multi‐directional excitation effects. This study examines the validity of this rule for irregular buildings. After identifying the principal direction of the irregular building, nonlinear static analyses were performed by applying seismic loads along either the principal direction or the analysis axes. The analysis results showed that the 100:30 combination rule produced non-conservative outcomes even for regular buildings, and this tendency became more pronounced in irregular buildings due to torsional effects. To address this issue, the 100:40 combination rule was also examined; however, no significant improvement was observed. In addition, this study proposed a simplified mode-shape–based method for identifying the principal direction, which yielded results comparable to those obtained with the more rigorous base-shear–based approach.

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    Reference

    Journal Abbreviation J. Earthq. Eng. Soc. Korea
    Frequency Bimonthly
    Doi Prefix 10.5000/EESK
    Year of Launching 1997
    Publisher Earthquake Engineering Society of Korea
    Indexed/Tracked/Covered By