slides earthquake resistant design part2
DESCRIPTION
This second part discusses about seismic design and detailingTRANSCRIPT
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Earthquake Design Considerations
By Dr. N. Subramanian3rd Nov. 2012
Dr. N. Subramanian
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Pounding between adjoiningbuildings due to horizontal vibrations
Dr. N. Subramanian
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More mass onone side causes the floors to twist
Dr. N. Subramanian
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One-side open ground storey buildingtwists during earthquake shaking
Dr. N. Subramanian
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Unequal vertical members cause building to twist about a vertical axis
Dr. N. Subramanian
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Waves of different periods
Dr. N. Subramanian
If the ground is shaken by earthquake waves that have short periods, then short period buildings will have large response.Similarly, if the earthquake ground motion has long period waves, then long period buildings will have larger response.
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Soil condition at site may influence damage
Dr. N. Subramanian
Different Buildings Respond Differentlyto Same Ground Vibration
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Design Codes
IS 13920, 1993, Indian Standard Code of Practice for Ductile Detailing of Reinforced Concrete Structures Subjected to Seismic Forces
IS 1893 (Part I), 2002, Indian Standard Criteria for Earthquake Resistant Design of Structures (5th Revision)
IS 4326, 1993, Indian Standard Code of Practice for Earthquake Resistant Design and Construction of Buildings (2nd Revision)
Dr. N. Subramanian
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Longitudinal steel in Beams
Dr. N. Subramanian
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Stirrups as per IS 13920
Dr. N. Subramanian
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Stirrups with 135 degree hooks at the end are required
Dr. N. Subramanian
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Lapping of Longitudinal bars
Dr. N. Subramanian
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Soft storey created by open GF car park
Dr. N. Subramanian
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Earthquakes do not kill people;man in his role as a builder, kills people.
Dr. N. Subramanian
Total Horz. EQ Force increases downwards along its heightCollapse of partially open GF building in Bhuj EQ, with vertical split at the middle!
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Possible plastic collapse mechanisms
Dr. N. Subramanian
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Strong-Column Weak –beam Principle
Dr. N. Subramanian
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Circular spiral columns Vs Rect. Columns in the same building during 1971 SFO EQ
Dr. N. Subramanian
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Column reinforcement
Dr. N. Subramanian
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Detailing of columns in seismic zones
Dr. N. Subramanian
180° links are necessary to prevent the 135° tie from bulging outwards
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Shear failure of column
Dr. N. Subramanian
Large spacing of ties and lack of 135° hook ends caused brittle failure of columns during 2001 Bhuj earthquake
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Buckling of column bars
Dr. N. Subramanian
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Confinement steel in columns
Dr. N. Subramanian
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Correct location for column splices
Dr. N. Subramanian
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Short Column effect
Dr. N. Subramanian
Short columns are stiffer and attract larger forces during earthquakes – this must be accounted for in design
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Short column effect
Dr. N. Subramanian
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Short column effect
Dr. N. Subramanian
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Detailing of short columns
Dr. N. Subramanian
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Beam-Column joints should be designed and detailed properly
Dr. N. Subramanian
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Detailing of beam-column joints
Dr. N. Subramanian
Ties with 135 degree hooks resists the ill effects of distortion of joints
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Pull-Push forces cause two problems
Dr. N. Subramanian
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Three stage procedure to provide horizontal ties in joints
Dr. N. Subramanian
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Anchorage of beam bars in interior joints
Dr. N. Subramanian
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Anchorage of beam bars in exterior joints
Dr. N. Subramanian
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Shear walls are to be placed symmetrically to avoid twist
Dr. N. Subramanian
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Detailing of shear walls as per IS 13920
Dr. N. Subramanian
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Collapse of nominally connected water tank
Dr. N. Subramanian
IS 1893 – Connections designed for five times the design horizontal acceleration coefficient
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Bare Vs infilled frame
Dr. N. Subramanian
Predominant frame action Predominant shear action
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Effect of infill walls
Dr. N. Subramanian
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Collapse of intermediate storey in 6 storey building, Bhuj, 2001
Dr. N. Subramanian
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Improper Anchorage into stiff RC elevator core walls in Ghandhidham
Dr. N. Subramanian
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Effect of Staircases
Dr. N. Subramanian
Diagonal slabs or beams in staircases attract large seismic forces-sliding supports limits the seismic forces
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Brick Buildings- Horz. Bands
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Base isolation of buildings to reduce shaking
Dr. N. Subramanian
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Base Isolation TechnologyOne 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
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Base isolated structure Conventional structure
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BASE ISOLATOR
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Base isolators may beeither coiled springs or laminated rubber-bearing pads, made of alternate layers ofsteel and rubber, and have a low lateral stiffness.
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Examples of Base Isolated Systems
Base Isolated LA City Hall
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San Francisco Airport International Terminal is the World’s Largest Base Isolated Building
Base isolator being installed. during a seismic event. Every isolator will extend in any direction 21 inches.
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Energy Absorbing Devices
• “Passive energy dissipation is an emerging technology that enhances the performance of buildings by adding damping to buildings.”
• (ASCE/SEI 41-06, pg 280)
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Commonly used dampersViscous dampers (They consist of a piston-cylinder
arrangement filled with a viscous silicon based fluid, which absorbs the energy)
Friction dampers (energy is absorbed by the friction between two layers, which are made to rub against each other).
Hysteretic dampers (energy is absorbed by yielding metallic parts)
Visco-elastic dampers (containing visco-elastic material, sandwiched between two steel plates, which undergoes shear deformation, thus dissipating energy.
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Other Types Of Dampers
Tuned mass dampers (TMD)- They are extra masses attached to the structure by a spring-dashpot system and designed to vibrate out of phase with the structure.
Tuned liquid dampers (TLD) – They are essentially water tanks mounted on structures and dissipate energy by the splashing of the water.
Hydraulic activators- They are active vibration control devices and have a sensor to sense the vibration and activate the activator to counter it. -Require external energy source and are expensive.
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Why Use Dampers?Dampers dramatically decrease earthquake induced
motion . Less displacement : over 50% reduction in drift in many
cases Decreased base shear and inter-story shear, up to 40% Much lower “g” forces in the structure. Equipment keeps
working and people are not injured Reduced displacements and forces can mean less steel.
This offsets the damper cost and can sometimes even reduce overall cost.
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Viscous Damper
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Example- Viscous damper
Dr. N. Subramanian
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Tuned Mass Damper (TMD)
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Taipei 101, the world's second tallest skyscraper is equipped with a tuned mass damper. This 18 feet dia.,730-ton TMD acts like a giant pendulum to counteract the building's movement--reducing sway due to wind by 30 to 40 %. Cost: $4 million
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