Abstract: The construction of a new 2.4 km long bridge, crossing the sea strait between the Croatian mainland and the Pelješac Peninsula to provide the fixed road link between the whole of Croatia, has just begun. The bridge location is in a highly seismic zone with the design ground acceleration of 0.41g and on extremely bad soil. The four-lane road bridge consists of two approach bridges and the main cable-stayed bridge with continuous steel trapezoidal box superstructure. Nonlinear modal time history analysis, based on superposition of Ritz vectors, but with coupled modal equations, was utilized for seismic design. Real earthquake accelerograms for earthquakes in the vicinity (Bar, Ulcinj, Ston) and also El Centro earthquake, as well as 72 artificial accelerograms, determined by seismic study for the specific bridge location, were analysed. The analysis was carried out taking into account the proposed construction sequence.