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

Base Isolation Strategies Seismic Base Isolation technology could effectively prevent disaster like this worldwide (Iran Roudbar-Manjil Earthquake 1990 40000 killed M=7.4) 26/04/2017 Base Isolation Strategies

Base Isolation Strategies We (Structural Engineers) are responsible to make the world safe to live 1990 Earthquakes with Magnitude 7.0 and Greater Vanuatu 7.1 Fiji Island 7.6 Costa Rica 7.3 Mariana Island Region 7.4 Minahassa , Indonesia 7.6 Sakhalin, Russia 7.2 Sudan (2 EQ) 7.1-7.2 Luzon, Philippines 7.7 Flores Sea 7.1 Romania 7.0 Panay, Philippines 7.1 Iran (Rudbar-Manjil) 7.4 Vanuatu 7.2 Papua New Guinea 7.5 26/04/2017 Base Isolation Strategies

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

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

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

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

Base Isolation Strategies 26/04/2017 IT REALLY WORKS ! Kobe Earthquake Japan 1995 FB vs. BI structure (Recorded acceleration & forces) Isolated structure 26/04/2017 Base Isolation Strategies

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

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

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

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

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

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

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

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

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

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

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

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