Supplemental Energy Dissipation With Prestressed Lead Extrusion Dampers (P-Led): Experiments and Modeling

Abstract

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.

Design and Experimental Assessment of a Prestressed Lead Damper with Straight Shaft for Seismic Protection of Structures

“…Two mechanisms contribute to the dissipation of energy, namely the plastic deformation of the lead material forced to flow through the annular orifice and the friction force activated between the lead core and the shaft [21,22]. Both mechanisms were demonstrated to be only weakly rate-dependent, so the energy dissipation capacity has a weak dependence on velocity too [11,23]. In the lead extrusion damper, part of the energy required to produce the plastic deformation of lead is dissipated as heat, while the other part is stored and used to promote the recrystallization of the deformed lead, by which the material regains its original properties; this mechanism results in consistent force across multiple cycles of response without any loss of strength or stiffness, or any other low-cycle fatigue effect [21].…”

“…The HF2V technology was practically employed in the Kilmore Street Medical Center in New Zealand, where the HF2V devices were used to develop a hybrid system, called the "Advanced-Flag Shape" system, to allow controlled rocking of the structure [27]. Further research on this technology was carried out by Soydan [14][15][16][17], Patel [36,37], Yang [37,38] and Quaglini [10,11]. The application of HF2V devices in structural connections of both precast structures and steel structures was studied in [29,33,35].…”

“…When the structure oscillates under the effects of the ground motion, the shaft moves relative to the tube, activating a friction force at the interface with the lead core, through which energy is dissipated. Since the coefficient of friction between lead and chromium-plated steel is noted to remain almost steady once sliding is triggered [11], the damper provides a constant force over its entire stroke and an ensuing essentially rectangular hysteretic curve, which maximizes the shaft cap tube lead core The assembly of the PS-LED consists of four main steps: (i) the lead core is cast in a hollow cylindrical mold with the outer and inner diameters resembling the diameters of the tube wall and the shaft, respectively; (ii) the lead core is fitted within the tube and the shaft is gently forced to pass through the lead core; (iii) the cap is locked to the tube wall by means of screws; by tightening the screws the lead core is prestressed and voids and clearances are removed, resulting in a perfect fit to the tube and the shaft; (iv) hinges are fitted to one end of the shaft and the opposite end of the tube to connect the damper to the structure. Possible configurations for installation of the PS-LED in a structural frame are based on placing the device within diagonal braces (Figure 3a), where the damper develops resistive forces against the brace elongation [41], or at both sides of the web (Figure 3b), where the device develops resistive forces against the beam rotation [35].…”

“…When the structure oscillates under the effects of the ground motion, the shaft moves relative to the tube, activating a friction force at the interface with the lead core, through which energy is dissipated. Since the coefficient of friction between lead and chromium-plated steel is noted to remain almost steady once sliding is triggered [11], the damper provides a constant force over its entire stroke and an ensuing essentially rectangular hysteretic curve, which maximizes the The damper is placed in conventional damped braced systems and connected at one end of the shaft and at the opposite end of the tube. When the structure oscillates under the effects of the ground motion, the shaft moves relative to the tube, activating a friction force at the interface with the lead core, through which energy is dissipated.…”

“…The design of energy dissipation devices meeting the needs of a resilient community should indeed fulfill multiple objectives [11,12]: (i) they should not require maintenance after a major earthquake, in order to guarantee a high safety level in case of aftershocks; (ii) they should not be at risk of low-cycle fatigue fracture, which is a typical issue for current steel hysteretic devices; (iii) they should ensure the recentering of the structure at the end of a seismic event; (iv) they should be a compact and architecturally lowly invasive in order to reduce the impact on the building layout; and (v) the cost of manufacturing and installation should be economically appealing compared with alternative design solutions such as structural strengthening.…”