The seismic isolation technology company-Quakesafe has boosted the seismic damping and mitigation technology to be as important as isolation sector. Based in Southwest China,it integrates its seismic isolation and damping expertise with involvement with consultation, structural analysis and design, manufacture, testing, installation, health monitoring of structures, maintenance and replacement.
Products
Pendulum isolator
Friction pendulum bearings (FPB) are made from two or more horizontal steel plates that can slide over each other because of their shape and an additional articulated slider. The bearings are placed between the bottom of a superstructure and its foundation (columns or piers).
They are designed to be very stiff and strong for vertical load, so that they can carry the weight of the superstructure. However, the fact that they slide means that earthquake movements can be accommodated through the collaboration work of the FPB systems. The spherical surfaces can be designed to extend the sliding as much as wanted, by choosing the radius of curvature of the concave surface
Before the seismic event takes place, FPB functions equal to a convention spherical bearing. Under earthquake, the fuse (shear pins) will break off, allowing the sliding between the spherical surfaces, able to isolate the structure from its foundation. Some of the kinetic energy is converted into potential energy during the sliding and the friction damping also turns the earthquake energy to heat. By doing so the effect of earthquake actions can be greatly mitigated. After the quake the re-centering property allows FPB to back to its normal working status.
The mass of the superstructure does not all affect the PFB design. The damping is determined by the sliding between stainless steel and modified PTFE to have a larger friction coefficient than pure PTFE or UHMWPE so more energy can be dissipated in the way of dispersed heat. The center of FPB and the supported structure automatically coincide with each other so the torsion effect is minimized. For the triple sliding FPB, there are totally 3 different radii to optimize performance for different earthquake expectations. The period, vertical load capacity, damping ratio, lateral stiffness and movement, uplift resistance force can be separately designed without relating to each other.
The following schemes illustrate the normal designs of FPB, single sliding and double sliding (with the same or different radius of the base plate and the top plate)
Elastomeric Isolator
General Concept
Elastomeric Isolator is also named as Seismic Isolation Bearing, or Base Isolator. Base isolation, also known as seismic base isolation or base isolation system, is one of the most popular means of protecting a structure against earthquake actions. It is a collection of structural elements which should substantially decouple a superstructure from its substructure resting on a shaking ground thus protecting the integrity of a building structure of a bridge structure.
Base isolation is one of the most powerful tools of earthquake engineering pertaining to the passive structural vibration control technologies. It is meant to enable the structure to survive a potentially devastating seismic impact through a proper initial design or subsequent modifications. In some cases, application of base isolation can raise both a structure's seismic performance and its seismic sustainability considerably. Contrary to popular approach such as increasing the strengthening resistance (larger foundation or thicker pillars. etc.), base isolation does not make a building earthquake proof but to protect the structure and its occupants inside from damage during seismic events.
Such base isolation technologies were utilized in the actual applications since 1960’S and proven during many happened earthquakes to be an effective method against seismic actions. Lead-core Rubber Bearing (LRB) and High Damping Rubber Bearing (HDRB) are among the most recognized means.
Viscous Fluid Damper (VFD)
Viscous damping has been widely used as the energy dissipation mechanism of choice in abating resonant vibration in structures. Damping of VFD for bridges and buildings is realized by the flow of low-viscosity fluid through the small openings (orifices).
Typical design includes piston, cylinder, viscous fluid, seal retainer, accumulator housing and mounting bracket. The piston splits the cylinder space into two chambers and the low-viscous fluid flows in and between the chambers repeatedly, along the piston rod moving in the cylinder. When the fluid passes the orifice on the piston, significant damping is generated so to dissipate the vibration energy during seismic events. Repeated back-and-forth of the piston converts the kinematic energy into the thermal energy until eventually dissipated completely along with the slow-down move of the piston.
Quality Capabilities
At Quakesafe, we promised to do, we did and we will do FPC (Factory Production Control) testing on each every piece of elastomeric isolator that we produce prior to delivery. Such testing standard is imposed according to the regulations established by local authorities, “Code for Performance Requirement and Test of Laminated Rubber Seismic Isolation Bearing for Buildings”, issued by Department of Housing and Urban-rural Development of Yunnan Province in 2013. It is equal to AASHTO standard “ Guide Specifications for Seismic Isolation Design, 4th edition”, however more stringent than EN15129 “Anti-seismic Devices” and the earlier specification “ISO 22762-3, Elastomeric Seismic-protection isolators, Applications for buildings-Specifications”.
| items | National standard | Quakesafe standard | comments |
| Extreme shear strain | 150%~300% | ≥ 400% | Equal to Japanese standard |
| Scope of sampling | For common structures, 20%; For major structures, 50%.If failure is detected,100% | 100% | Each isolator is tested as per FPC test items |
| Allowed shear stiffness variance | As per ISO:22762, for S-A category, individual variance shall be within ±15% and mean value shall be within ±10%; For S-B category, ±25% and ±20% respectively. | S-A only | Higher category is imposed at Quakesafe |
| Horizontal deflection (under V.load) | ≤5mm for all sizes | For D≤ 600mm ones, ≤ 600mm3mm; Above that, ≤ 600mm5mm. | More assure the uniform performance in a batch |
| Service life | ≥50 years (typically) | ≥80 years (typically) |
he image discloses Quakesafe’s bearing is under 410% shear and no any sign of failure (D=1000mm, total thickness of elastomer is 200mm and shear deformation reaches 820mm).
3 compression-shear testing at different ratings are built inside Quakesafe manufacturing base to meet the onerous testing tasks. The max. vertical load as of date reaches 1,500 tons (with 10% shear load and±250mm as horizontal displacement) and a 5,000 tons test machine is expected to operate in summer of 2020, which is also the 4th testing machine that is owned by Quakesafe.
Various testing equipment is also laid in-house to control the consistency of rubber quality, which is checked on a regular basis as per the local regulations.
QUALITY
Model of the under-design 5,000 tons compression-shear testing platform
Apploication
