This paper presents a study on the seismic nonlinear performance of 86 multistory dual systems irregular in elevation and constructed from normal strength concrete (with fc = 25 MPa) and high-strength concrete (with fc = 75 MPa). The applicability of the Static Equivalent Lateral Force (SELF) method used by the seismic codes in Europe (Eurocode 8), in the United States (IBC-2012) and in Egypt (EC201-2008) when applied to dual systems irregular in elevation and constructed from NSC and HSC is examined. In addition, the reliability of the criteria provided by the studied codes, in order to separate the regular from irregular dual systems is also verified. Records of two real earthquakes (El Centro and Parkfield) and one artificial earthquake, with wide ranges of frequency content have been selected as input ground motions. The results showed that the limits in IBC-2012 and EC201-2008 aimed to identify the lateral stiffness irregularity are satisfactory and can be relaxed by about 10%.