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Seismic Behaviour of Steel Structures
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Teaching Resources © IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta 1
SEISMIC BEHAVIOUR OF STEEL STRUCTURES
Teaching Resources © IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta 2
Seismic Behaviour of Structural Steel
• Ductile, equally strong in compression and tension
• Mild versus high strength steel
• Produced with high quality control. Aids in Capacity Design yield ratio = expected yield strength/specified min. yield strength
• Welding subjected to fatigue
SEISMIC BEHAVIOUR OF STEEL STRUCTURES
Robustness of Steel Structures
Teaching Resources © IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta 3
SEISMIC BEHAVIOUR OF BRACING MEMBERS
Fig. 6 Hysteretic behaviour of a slender brace
P(comp.)
2
0-1-2 2 3 41-3-4-5-2
-1
0
1
5
P(ten.)
buckling
P• Bracings used either for lateral strength or for lateral stiffness
• used in pairs
• slenderness limited to a value such that C = T/2
• solid cross-sections preferred
Teaching Resources © IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta 4
SEISMIC BEHAVIOUR OF BEAM-COLUMNS
Seismic Behaviour of I-sections
Hysteretic behaviour of an I-section
M/My
/y
Teaching Resources © IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta 5
Seismic Behaviour of Rectangular Hollow Sections (RHS)
M/My
/y
Hysteretic behaviour of rectangular hollow section
SEISMIC BEHAVIOUR OF BEAM-COLUMNS-1
Teaching Resources © IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta 6
Seismic Behaviour of Circular Hollow Sections (CHS)
M/My
/y
Hysteretic behaviour of circular hollow section
SEISMIC BEHAVIOUR OF BEAM-COLUMNS-2
Teaching Resources © IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta 7
Seismic Behaviour of Concrete-Filled Tubes (CFT)
Failure Mode of a concrete-filled RHS
SEISMIC BEHAVIOUR OF BEAM-COLUMNS-3
• Efficient use of steel
• Concrete in confined state
• Local buckling delayed in RHS
Teaching Resources © IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta 8
Types of moment connections
(a) (b)
(c) (d)
SEISMIC BEHAVIOUR OF CONNECTIONS
Teaching Resources © IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta 9
5
2
0-1-2 2 3 41-3-4-5-2
-1
0
1
M/My
/y
Hysteretic behaviour of bolted angle connection
SEISMIC BEHAVIOUR OF CONNECTIONS-1
Teaching Resources © IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta 10
Sway frames and non-say framesBraced and un-braced frames
Concentrically Braced Frames (CBF)Eccentrically Braced Frames (EBF)
(a)Diagonal bracing
(b)Cross or X-bracing
(c )Chevron bracing
(d)Eccentric bracing
Link Beams
Bracing systems in Steel Frames
SEISMIC BEHAVIOUR OF FRAMES
Teaching Resources © IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta 11
Failure of ConcentricBraced Frames
Teaching Resources © IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta 12
Desired and Undesired Collapse Mechanisms in Capacity Design
(a) Desired (b) Undesired
CAPACITY DESIGN
Teaching Resources © IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta 13
LeadPlug
Laminated rubber bearing pad
SPECIAL DEVICES AND SYSTEMS
Either isolate or dissipate
Base Isolation
Vibration Control Active and Passive
Visco-elastic dampers used assliding supports for beams/trusses
Tuned Mass Dampers(TMD)
Tuned Liquid Dampers(TLD)
Hydraulic Actuators
Weak links, stoppers etc as inelastic dampers