1. Base Isolation Strategies
26/04/2017
Base Isolation strategies for steel frame structures CE510 Presentation By: H- Adib CONTENT
1- Seismic base isolation & the philosophy behind it
2-Types of conventional seismic base isolation
3- seismic base isolation in steel frame structures & rehabilitation of existing structures
4-Base isolation advantages & defficiencies
26/04/2017
Base Isolation Strategies

2. Base Isolation Strategies
Seismic Base Isolation technology could effectively prevent disaster like this worldwide (Iran Roudbar-Manjil Earthquake killed M=7.4)
26/04/2017
Base Isolation Strategies

3. Base Isolation Strategies
We (Structural Engineers) are responsible to make the world safe to live Earthquakes with Magnitude 7.0 and Greater
Vanuatu
Fiji Island
Costa Rica
Mariana Island Region
Minahassa , Indonesia
Sakhalin, Russia
Sudan (2 EQ)
Luzon, Philippines
Flores Sea
Romania
Panay, Philippines
Iran (Rudbar-Manjil)
Vanuatu
Papua New Guinea
26/04/2017
Base Isolation Strategies

4. SEISMIC BASE ISOLATION GENERAL DIFINITION
Structural vibration control technology (at foundation )in seismic design of structures is called Base Isolation.
A base isolation device is a flexible interface between the superstructure and ground foundation that can considerably reduce the level of earthquake forces transmitted to the building
24/03/2011
Base Isolation Strategies
By: H-Adib

5. Deficiencies in non-isolated(Fixed Based) design of structures
If ductile large inter story drift and possible residual deformation after intensive earthquake
If stiff and rigid high floor acceleration will create damage to the sensitive contents & none-structural components and
possible brittle failure in the structural element
26/04/2017
Base Isolation Strategies

6. SEISMIC BASE ISOLATION TECHNOLOGY
One of the most significant developments in earthquake engineering in the past 35 years
It provides the design profession the ability to design a building that is “operational” after a major earthquake
26/04/2017
Base Isolation Strategies

7. Base Isolation Strategies
BASE ISOLATION CAPABILITIES Conventional (Fixed base) VS Base Isolated Structures
During an 8 Richter Magnitude Earthquake a Seismically Isolated Building Will Behave as if it Were Experiencing a 5.5 Earthquake
Forces reduces by 3 to 6 across the isolator in BI structure
Forces reduces by 8-12 At the roof in a BI structure
Ground forces will amplify by a factor of 3 to 4 In conventional (Fixed Base) structures
26/04/2017
Base Isolation Strategies

8. Base Isolation Strategies
26/04/2017
IT REALLY WORKS ! Kobe Earthquake Japan FB vs. BI structure (Recorded acceleration & forces)
Isolated structure
26/04/2017
Base Isolation Strategies

9. Base Isolation Strategies
Conventional Building Kobe Earthquake Recorded acceleration amplification
Steel frame structure
Superstructure consist of braced frames with fixed-based period of 0.68 sec.
The target period of the isolation system is up to 3.3 sec. for displacement of 240mm
Isolators are lead-plug rubber bearing and high-damping rubber bearing with diameter of 1.2m
26/04/2017
Base Isolation Strategies

10. Base isolation strategies
Philosophy behind the base isolation system (Acceleration & Displacement Response Spectra)
26/04/2017
Base isolation strategies

11. Type of Seismic Base isolation
Elastomeric isolators (natural rubber or high-damping elastomer & steel reinforced plates)
Sliding isolators (Teflon- Stainless Steel)
Combination system Sliding for friction & Elastomeric for re-centering capabilities
26/04/2017
Base Isolation Strategies

12. Types of Seismic Base Isolation Device
Laminated rubber bearing with lead core.
Elastoeric bearing

13. Friction pendulum system FPS specifications
Friction Pendulum system combines sliding action and re-storing force by geometry
The effective stiffness of the isolator and the isolation period of structure is controlled by radius of concave surface
The coefficient of friction depends on pressure and sliding velocity
26/04/2017
Base Isolation strategies

14. Friction Pendulum Bearing
STAINLESS STEEL
CONCAVE SURFACE
HOUSING
PLATE
PLATE
CONCAVE
SELF LUBRICATING
COMPOSITE LINER
ARTICULATING
SLIDER
SECTION
Base isolation Strategies

15. Basic requirements of seismic isolation system
Sufficient horizontal flexibility to lengthen the building period, while maintaining the vertical stiffness
Sufficient damping to restrict the relative deformation at the plane of isolation & limit it to bearing capacity
Sufficient stiffness to prevent damage under service load (wind load)
Small residual horizontal displacements after an earthquakes( Re-centering capability)
26/04/2017
Base Isolation Strategies

16. Base Isolation Strategies
International terminal at Sanfrancisco airport largest base isolated steel structure in the world
276 Seismic isolators
Friction Pendulum sliding (F
Cast steel bearing consist of a stainless steel spherical surface with articulated slider
Allowable lateral isolator displacement of 20 in.
Provide isolation of 3 sec
Reduces Earthquake force demand on supper-structure by 30% of the demand for the fixed-base structure
BI structure Remain elastic & undamaged under PGA=0.6g
26/04/2017
Base Isolation Strategies

17. Base Isolation Strategies
Base Isolation strategies in rehabilitation (retrofit) of existing structures(Oakland city hall)
Work maybe Confined to Basement
Building Can Continue to be Occupied
Often the Most Economic Solution
26/04/2017
Base Isolation Strategies

18. Base Isolation with so much capability why not implemented world wide?
Seismic base isolators are large and heavy some could weight 1 ton or more
Expensive design-fabrication & construction cost from $5000 and up
Too much design provision to be implemented(eg.2 specimen to be tested for each BI type)
26/04/2017
Base Isolation Strategies

19. Farther research and experimental studies must be conducted on production & implementation of low cost base isolators
To extend this effective earthquake-resistant strategy to housing and commercial buildings specially in developing country the cost and weight of the isolators must be reduced
Design provision and requirements should be simplified
Steel plate reinforcement layers in the isolator elastomer may be replaced by high strength low weight reinforcement fibers like carbon or glass fibers
26/04/2017

20. Base Isolation Strategies
REFERENCESS
Dynamics of structures –third edition-Anil K. Chopra
Earthquake resistance design with rubber-second edition-James M . Kelly
Earthquake Engineering 2004-Yousef Bozorgnia & Vitelmo V. Bertero
Design of seismic isolated structures - Farzad Naeim & James M. Kelly
26/04/2017
Base Isolation Strategies