The confined wall structure (CWS) of medium-rise buildings are generally built with walls of the same thickness. It causes stress at the bottom wall-story to become the highest. Numerical analysis was conducted to evaluate the behavior of CWS with wall density index variations. Three 4-story CWS buildings with different wall thicknesses were modeled in finite element software. Model 1 (M1) considered the same wall thickness for the whole building; M2 and M3 varied the thickness where the top

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... or wall was the thinnest. The calculation of wall density index (WDI) was performed on all three models. The results showed that the value of WDI calculated using the transformation method is the closest because it takes into account the differences in material quality and its value meets the standard requirements. Analysis results showed that the drift ratio for all three models were less than 0.2%, which also fulfilled the requirement. However, M3 showed the highest displacement. Compressive stress, tensile stress, and shear stress for M1 and M3 models satisfied the allowable stresses, but maximum compressive stress on the top-level wall of M2 exceeded the permitted stress.