Bull Earthquake Eng (2011) 9:1499–1518 DOI 10.1007/s10518-011-9258-2 ORIGINAL RESEARCH PAPER Intensity measures for response prediction of a torsional building subjected to bi-directional earthquake ground motion Andrea Lucchini · Fabrizio Mollaioli · Giorgio Monti Received: 20 August 2010 / Accepted: 6 March 2011 / Published online: 29 March 2011 © Springer Science+Business Media B.V. 2011 Abstract In the framework of performance-based assessment of existing RC buildings, an important step is the definition of an intensity measure (IM) of the seismic action that be accurate and efficient in correlating with the engineering demand parameters (EDP) of interest and in reducing the variability in their prediction. Objective of this work is to assess five different IMs, when they are applied to an in-plan irregular three-dimensional building subjected to bi-directional earthquake motion. The objective is pursued through multiple regression of the results obtained from nonlinear dynamic analyses. The study shows that certain IMs are more suitable to evaluate EDPs when dealing with 3D structures subjected to 2D earthquakes. Keywords Intensity measures · Seismic response predictors · Torsional building · Bi-directional earthquake 1 Introduction In the framework of performance assessment, a fundamental step involves the prediction of demands on the building system as a function of the seismic action intensity, that is, the definition of functional relationships between a (vector of) meaningful engineering demand parameter(s) (EDP) and a (vector of) given earthquake intensity measure(s) (IM). The former identifies quantities of relevance for damage and losses to the building system (not necessarily of structural nature), while the latter defines the seismic input to the structure. Such functional relationships are usually obtained from simulations, which eventually lead in the contest of probabilistic seismic demand analyses to a function of the type (Cornell and Krawinkler 2000) G(EDP|IM) expressing the probability of EDP conditioned to IM. A. Lucchini (B ) · F. Mollaioli · G. Monti Department of Structural Engineering and Geotechnics, Sapienza University of Rome, Via Gramsci 53, 00197 Rome, Italy e-mail: andrea.lucchini@uniroma1.it 123