The analysis was done to determine seismic response values such as peak base shear, peak displacement and peak interstory drift ratio. Further, modal analysis was done. The results show that coupled irregular building models yield peak base shear response in both principal directions under unidirectional seismic force unlike regular building. Modal analysis results indicate coupled irregularities in building models yield coupled contribution of transnational and rotational degrees of freedom in fundamental modes of vibration. Coupled irregular models show amplified peak displacement and peak interstory drift ratio at each floor as compared to regular building models. The authors conclude that coupled irregularity in building models yield seismic amplification in various seismic response parameters, thus making them seismic vulnerable.

The second paper is "Seismic Fragility Estimates of Regular and Irregular Structures with Different Soil Conditions Using Time History Analysis" by Ramesh B M, K Manjunatha and Ravikumar C M. Here an attempt has been made to analyze regular and vertically irregular structures using time history analysis approach to establish seismic fragility.

The study highlights the importance of obtaining the performance of buildings in terms of operational phase, immediate occupancy, damage control, life safety and collapse prevention. A graph of seismic intensity measurement versus likelihood of a seismic damage condition is called a fragility curve. With such curves, estimation of likely damage occurrence in the buildings can be found. Several models of the regular and irregular buildings have been considered for the analysis.

The time history analysis has considered three Indian Strong Ground Motion records under different soil conditions. Time history analysis is a nonlinear dynamic analysis that uses the finite element approach or direct integration. It takes a minimum of three sets of ground motions to complete a time history analysis. The data obtained has been plotted for comparison. The soil conditions are represented by the use of hard, medium and soft springs to represent different soil conditions.

The analysis reveals that a building founded on soft soil has the largest time period, and as soil gets stiffer, the time period becomes less and less. Irregular buildings show more story displacements as compared to regular buildings for all soil conditions. The fragility curves have been plotted for the regular and irregular buildings under various peak ground acceleration conditions. The fragility condition curves show the level of damages which a building will undergo in a particular condition.

The results indicate that the soil conditions play an important role in the performance of structures. Time period for a regular building is larger than the irregular building. Geometrically, irregular buildings will have more story displacements than a regular building. Spectral accelerations has the highest peak values for fixed base case in all building models considered. Irregular buildings are more vulnerable to suffer damages during seismic excitation.