Design procedures for DCS implementation. Report to European Commission No. EVG1-CT-1999-00013 SPIDER/8.1-2/UDINE/SSO/03/VF-C, Deliverable No. 17. Research and Technological Development Project SPIDER, August 2002

This report describes a specially conceived procedure for the design of the damped cable system (DCS). The procedure is formulated according with a performance-based non-linear dynamic approach, and consists of a preliminary and a final verification phases. The former phase is carried out by referring first to a modal transformation, and then to a single-degree-of-freedom (SDOF) dynamic idealisation of the building protected by DCS. Both schemes derive from simplified assumptions on the structural characteristics and the cable geometry, as well as on the design hypothesis of preserving a first mode-dominated seismic response also in protected conditions. The cable geometry is traced out at this stage of the analysis with the aim of approaching – within the limits imposed by the architectural constraints and the actual structural configuration – a parabolic layout, or the “constant horizontal force” one. In fact, these represent the two most performing shapes highlighted by the extensive parametric analyses carried out by Udine University team within the context of Work-Package 1, as well as in the subsequent numerical investigations developed on selected case studies [1-3]. The solving equations of motion are explicitly formulated for the non-linear dynamic SDOF problem, which can nevertheless be modelled also by commercial calculus programs including non-linear viscous dashpot elements in their basic libraries, among which the widely used SAP2000NL code. The four-step preliminary phase is carried out by referring to the highest hazard level assumed in the performance-based approach, although additional checks can also be developed with regards to the remaining levels. The procedure is started by imposing a target reduction on the fundamental period of the unprotected structure, from which the preliminary values of cable-section area, and of first and second-branch Jarret device stiffness are determined (steps 1 and 2). The cable and device pre-loads are then evaluated by a separate criterion, where the limit top displacement of the building deemed compatible with the highest hazard level-related design objective is input (step 3). The preliminary choice of the damping coefficient of Jarret device is finally located by a parametric enquiry based on the proposed dynamic SDOF model (step 4).