Design Procedure and Behaviour of Advanced Flag- Shape (AFS) MDOF Systems


A. Palermo
Department of Structural Engineering, Politecnico di Milano, Milan, Italy
S. Pampanin, W. Y. Kam and A. J. Carr
Department of Civil Engineering, University of Canterbury, Christchurch, New Zealand

Presented at New Zealand Society for Earthquake Engineering Annual Conference (NZSEE08), New Zealand, 2008.

In this contribution, the concept of AFS systems is extended to MDOF systems. Preliminary suggestions for a simplified design procedure for AFS connection systems are given within the framework of a Direct Displacement-Based Design (DDBD) approach. Using case-study prototypes of five-storey moment-resisting frame, incorporating four different connection systems, a comparative MDOF study is carried out by the means of non-linear time-history analyses using suites of far-field and nearfault earthquake excitations. The non-linear time history analysis results for both far-field and near-fault earthquakes provided satisfactory validation of the design procedure, though being, as expected, on the conservative side when dealing with velocity-dependent dissipating systems.

In the search of alternative retrofit techniques and new seismic-resisting systems that would perform to the performance objectives in line with the framework of the Performance-based Earthquake Engineering (PBEE), structural systems with the emphasis on minimising damage and financial losses have been recently developed. The introduction of jointed-ductile precast concrete systems (typically referred to as PRESSS-technology), where un-bonded post-tensioned tendons are used in conjunction with hysteretic energy dissipation elements to achieve self-centering capacity, hence guaranteeing negligible residual deformation on the structural systems and assuring minimum damage in the structural elements (Priestley et al., 1999), is considered one of the main seismic research outcome highlights of the past decade. Further research in the development of re-centering systems based on a controlled rocking motion has extended its application to steel (Christopoulos et al., 2002) and timber structures (Palermo et al., 2005). In parallel, investigations have been carried out on the feasibility of combining re-centering systems with viscous damping (Kurama, 2001) or friction energy dissipation devices (Morgen and Kurama, 2004). In conjunction to the development of these new structural system, the argument to use a residual deformation damage index (RDDI), in combination to traditional damage indexes based on ductility, maximum displacement and/or cumulated energy, as a more appropriate damage indicator was made (Pampanin et al., 2002). Recognising that minimal residual deformation as a critical component of a design objectives, as with maximum displacements, better performance levels can be achieved with re-centering structural systems.

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