Seismic Behaviour of Steel Structures

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

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SEISMIC BEHAVIOUR OF BEAM-COLUMNS

Seismic Behaviour of I-sections

Hysteretic behaviour of an I-section

M/My

/y

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Seismic Behaviour of Rectangular Hollow Sections (RHS)

M/My

/y

Hysteretic behaviour of rectangular hollow section

SEISMIC BEHAVIOUR OF BEAM-COLUMNS-1

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Seismic Behaviour of Circular Hollow Sections (CHS)

M/My

/y

Hysteretic behaviour of circular hollow section

SEISMIC BEHAVIOUR OF BEAM-COLUMNS-2

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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

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Types of moment connections

(a) (b)

(c) (d)

SEISMIC BEHAVIOUR OF CONNECTIONS

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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

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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

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Failure of ConcentricBraced Frames

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Desired and Undesired Collapse Mechanisms in Capacity Design

(a) Desired (b) Undesired

CAPACITY DESIGN

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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