The anti-seismic and vibration damping devices are used to modify the response of a structure to a seismic or dynamic action. It can be done by seismic isolation, by energy dissipation, or by the introduction of temporary or permanent connection devices.
They can be used in buildings, bridges/viaducts, or any other structure.
Typologies
Elastomeric isolators are made up of rubber layers alternating with steel laminates joined together through vulcanization. Their behaviour can be modelled as linear, by means of effective stiffness and equivalent viscous damping. Usually they are manufactured with High Damping Rubber compound, i.e. with equivalent viscous damping 15% at 100% shear strain (HDRB).
Classification
- SI – [type of rubber compound] [diameter of the elastomer (mm)] / [thickness of the internal elastomeric layers (mm)]
Lead Rubber Bearings (LRBs) are elastomeric isolators with one or more lead plugs, inserted with the aim to increase the damping by hysteretic shear deformations of the lead. The equivalent viscous damping can be up to 30%. Their constitutive behaviour results bilinear.
Classification
- LRB – [type of rubber compound] [diameter of the elastomer (mm)] / [thickness of the internal elastomeric layers (mm)] – [diameter of the internal lead core(mm)]
The Curved Surface Sliders or Pendulum isolators use gravity as the restoring force. Energy dissipation is provided by friction. The parameters of the bilinear constitutive law depend on the radius of curvature and friction coefficient. The can be designed and manufactured in two main types, with one (FIP series) or two (FIP-D series) primary spherical sliding surfaces that accommodate the horizontal displacement. Usually FIP-D series is preferred because of the smaller plan dimension.
Classification
- FIP – [type of friction] [conventional number] / [total displacement (mm)] ( radius of curvature (mm) )
- FIP-D – [type of friction] [conventional number] / [total displacement (mm)] ( radius of curvature (mm) )
These isolators combine in a single device a slider and dampers, that typically are steel hysteretic and/or fluid viscous dampers. Thus, the resulting behaviour is characterised by a very high energy dissipation capacity. The slider can be free-sliding or guided, as required. The isolator can also combine STUs or mechanical fuse restraints.
Fluid Viscous Dampers are cylinder/piston devices that exploit the reaction force of silicone fluid forced to flow through an orifice and/or valve system. The typical force-velocity law is non-linear, i.e. F=Cvα, where α =0.15, F is the force, C is the damping constant and v is the velocity. Different values of the α exponent can be provided on request.
Classification
- OTP [assial load (tons)] / [total stroke (mm)]
- OP [assial load (tons)] / [total stroke (mm)]
Fluid spring dampers are cylinder/piston devices whose reaction force F depend on both imposed velocity v and displacement x according to the law F=F0+Kx+Cvα , where F0 is the pre-load force, K is the stiffness, C is the damping constant and α=0.15. The pre-load force can be useful to avoid displacements under service horizontal loads (e.g. braking forces in a bridge).
Steel Hysteretic Dampers use as a source of energy dissipation the hysteretic yielding of steel elements of various shapes, developed to guarantee many stable hysteresis loops. The most used elements in bridges, as components of the seismic isolation system, are the crescent moon and the tapered pin (single or double). In buildings, Buckling Restrained Axial Dampers (BRAD®) are often used within dissipative braces, in particular for seismic retrofit of existing buildings.
Shock Transmission Units (STUs) provide a very stiff dynamic connection, whilst their reaction to low velocity applied displacements, e.g. due to thermal changes, is negligible. STUs find valid application whenever the structure is requested to change its behaviour in the event of earthquakes or other dynamic actions. Sometimes STUs are also referred to as lock-up devices.
Classification
- OT [assial load (tons)] / [total stroke (mm)]
Mechanical Fuse Restraints (MFRs) below a pre-established force threshold prevent relative movement between connected parts, whilst they permit movements after the aforesaid threshold has been exceeded, provoking the breakaway of sacrificial components. Movements can be in one or any direction; i.e. a MFR can be designed to become a guide bearing after breakaway.
Shape Memory Alloy Devices (SMAD®) are axial restraint devices exploiting the superelastic properties of shape memory alloys in the austenitic state. Their force-displacement curve exhibiting one or more “plateaux” enables SMAD® to limit the maximum load transmitted to the structure to which they are connected. They have a strong recentring capability.
Tuned Mass Dampers (TMD) comprise a mass/spring/damper system attached to a structure to reduce its dynamic response. The frequency of the TMD is tuned to the fundamental frequency of the structure so that when that frequency is excited, the TMD will resonate out of phase with the structural motion.
TMD are especially suitable to be used in flexible structures affected by external phenomena characterized by a range of disturbance frequencies such as to interfere with the fundamental frequency of the structure. Said devices are therefore applied to walkways, cable-stayed bridges, stadium roofs and terraces, chimneys, towers and skyscrapers etc.
ISOLART® is a family of special devices developed for seismic isolation of art works, but that can be used for other light objects as well, such as containers, servers, critical or sensitive equipments, etc.
These products are subdivided into ISOLART® PENDULUM, which is based on the principle of simple pendulum, and ISOLART® SMA, patented system based on the superelastic behaviour of the shape memory alloys.
