The assessment of the seismic performance depends on the choice of the earthquake Intensity Measure (IM). During the past years many IMs, which take into account not only earthquake characteristics but also structural information, have been proposed. However, no consensus on which IM is the best predictor of the seismic response exists. Along these lines, the objective of this paper is to present the various developed scalar structure-specific seismic IMs and the problems associated with their use in practice, so that the engineer may become familiar with them and their implications in the context of Performance-Based Earthquake Engineering.

The objective of this paper is the investigation of the influence of the seismic incident angle on the response values of symmetric in plan buildings subjected to bi-directional horizontal ground motion. Firstly, a set of symmetric buildings is studied by means of linear response history analysis. The maximum response values over all incident angles are determined using well established analytical formulae. It is demonstrated that for symmetric buildings possessing equal stiffness along two orthogonal horizontal axes the maximum value of some vectorial response quantities (resultant displacements, resultant moments of some columns) does not depend on the orientation of the seismic action. On the contrary, the seismic incident angle is essential for the rest response quantities of such buildings, as well as for all the response quantities of symmetric buildings with different stiffness along the two structural axes. In addition, the same buildings are analyzed by means of non-linear response history analysis, with seismic components having several different orientations with regard to the structural axes. Similar conclusions are derived for the nonlinear range of behaviour too.