Axial hysteretic seismic dissipators with impeded instability C.M.M. ISTER-AX
The ISTER-AX model is a hysteretic BRB (Buckling-Restrained Braces) type heat sink, that is an axial hysteretic dissipator with impeded instability.
In this type of device the dissipative element has a linear shape and is engaged exclusively with axial load: the single damping element therefore acts in traction-compression, guaranteeing the complete plasticization of the section due to the applied axial force.
For these devices, obviously, one of the main requirements is the prevention of the instability of the damping component subjected to the compression load: to do this, it is inserted inside a steel tube and confined by means of a mortar jet to high anti-shrinkage resistance; the interposition of a sheath allows the damping element to deform axially without transmitting tangential forces to the confinement material.
This type of heat sink is widely used for seismic adaptation projects of existing structures (buildings, schools, hospitals, etc.), where it is often used as a dissipative upwind or as a dissipative element placed at the end of steel bracing.
The typical force-displacement behaviour of the first load branch of the device can be modelled as bi-linear, as shown in the following diagram where the nominal behaviour is compared to the typical experimental one:
In this type of device the dissipative element has a linear shape and is engaged exclusively with axial load: the single damping element therefore acts in traction-compression, guaranteeing the complete plasticization of the section due to the applied axial force.
For these devices, obviously, one of the main requirements is the prevention of the instability of the damping component subjected to the compression load: to do this, it is inserted inside a steel tube and confined by means of a mortar jet to high anti-shrinkage resistance; the interposition of a sheath allows the damping element to deform axially without transmitting tangential forces to the confinement material.
This type of heat sink is widely used for seismic adaptation projects of existing structures (buildings, schools, hospitals, etc.), where it is often used as a dissipative upwind or as a dissipative element placed at the end of steel bracing.
The typical force-displacement behaviour of the first load branch of the device can be modelled as bi-linear, as shown in the following diagram where the nominal behaviour is compared to the typical experimental one:
The typical force-displacement ratio of an entire cyclic opening-closing test is shown in the following figures (nominal behaviour and experimental graph). The entire cyclic behaviour can provide a damping capacity of over 40%.
* the value of Fu may be slightly different in opening and closing due to the heat sink configuration.
The high initial stiffness of the element (with low displacements) is useful to guarantee a rigid behaviour in service (static condition, wind load).
The maximum displacements obtainable with this type of damper are of the order of +/- 200mm.
The high initial stiffness of the element (with low displacements) is useful to guarantee a rigid behaviour in service (static condition, wind load).
The maximum displacements obtainable with this type of damper are of the order of +/- 200mm.
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