Supplemental energy dissipation with Prestressed Lead Extrusion Dampers (P-LED): experiments and modeling

Supplemental energy dissipation devices are employed both in new and retrofitted constructions in order to prevent structural damage, increase life-safety and achieve a desired level of performance. Among these devices, hysteretic dampers have been proven to be an appropriate and economically affordable solution to reduce the vulnerability of ordinary structures, such as residential, school and industrial buildings. The study presents an experimental and numerical investigation of a Prestressed Lead Extrusion Damper (P-LED), an emerging energy dissipation device which provides energy dissipation by means of the plastic extrusion of lead through an orifice created between a containing tube and a moving shaft and achieves high specific output force by preloading of the working material. The experimental investigation is performed following the provisions set in the European standard EN 15129 for Displacement Dependent Devices. A damper prototype is tested in cyclic tests at different displacement amplitudes and in a monotonic ramp up to the amplified design deformation. The damper shows a rigid-plastic behavior, without strength degradation regardless of the imposed deflection; the shape of the hysteresis loops is essentially rectangular, resulting in an effective damping of 0.55, very close to the maximum theoretical level; the device is able to sustain multiple cycles of motion at the basic design earthquake displacement, anticipating a maintenance-free operation even in presence of repeated ground shakes. A 3D finite element model of the P-LED is formulated in Abaqus and validated upon the results of the experimental tests. The model enlightens that the output force of the damper accounts for two contributions, namely the extrusion force of the lead and the friction force between the lead and the moving shaft. The model is then used in a parametric study to investigate the influence of the device dimensions, namely the diameters of the shaft, of the containing tube and of the bulge, and the length of the shaft, on the output force. The numerical data points are fitted by a simple model which can be used for design of the damper to a specific quasi-static force.