I have recently modelled some viscous and viscoelastic dampers in toggle brace arrangement in a 6 storey moment resisting steel frame and maximum floor displacement has been reduced drastically, but surprisingly base shear and maximum floor acceleration have increased by 20% or maybe more.
I wonder if adding such devices should always decrease base shear or floor acceleration?
Structural control systems have been greatly improved during the last 3 decades to confront natural hazards such as wind and earthquakes. Three main types of structural control systems are used:
1) passive control systems, with high energy dissipation density and no need of an external power source;
2) active control systems, with force delivery devices and real-time processing sensors that need power for the actuator to generate a structural control force; and
3) semi-active control systems, that change some structural parameters while consuming less power compared with active control systems.
The two general categories of passive damper devices are rate independent and rate dependent. Rate independent type involves metallic yielding or hysteretic and friction devices. The yielding mechanism is such that the energy dissipation component is inactive in confronting low levels of ground motion while in case of high levels of ground motion sliding friction or metallic yielding provides the energy dissipation. This class of damper increases the lateral stiffness of structure. Rise of lateral stiffness along with dissipation of energy may result in lower system deformation, but high story accelerations. Viscous fluid dampers (VFDs) and viscoelastic (VE) solid dampers belong to rate dependent passive dampers. Behavior of VE rubber dampers is a rate dependent phenomenon. viscoelastic dampers (VEDs) take advantage of shear deformation of viscoelastic materials (VEM). The typical configuration of VEDs is such that the VEM is bonded between steel plates to dissipate oscillation energy. This manner of damping reduces floor acceleration, interstory displacement and interstory shear. VEDs are able to dissipate energy against all levels of ground motion. Generally speaking, VEDs are known as some of most efficient vibration control devices in strengthening existing and new buildings against wind and earthquake.
However, since it is not easy to reach to a balance between stiffness and damping and depending the type of VED you applied and also the levels of ground motion applied the result for base shear may be different, but generally speaking the rate independent type passive dampers increase the lateral stiffness of structure and the rise of lateral stiffness along with dissipation of energy may result in lower system deformation, but high story accelerations. On other hand the behavior of VE rubber dampers is a rate dependent phenomenon and this type of VEDs take advantage of shear deformation of viscoelastic materials (VEM) and the typical configuration of VEDs to dissipate oscillation energy and this manner of damping reduces floor acceleration, interstory displacement and interstory shear.
I hope it is helpful to you.
All the best.
thanks for your helpful answer, but in all viscous cases that we modeled, the base shear increases unreasonable. and we don't know the reason of this result.
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Materials
- Inorganic Materials
- Metals
- Alloys
- Steel