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 4 1 -3 -4 -5 -2

-1

0

1

5

P (ten.)

d

buckling

d

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

f/fy

Teaching Resources © IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta 5

Seismic Behaviour of Rectangular Hollow Sections (RHS)

M/My

f/fy

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

f/fy

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 4 1 -3 -4 -5 -2

-1

0

1 M/My

f/fy

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 frames Braced 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 Concentric Braced Frames

Teaching Resources © IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta 12

Desired and Undesired Collapse Mechanisms in Capacity Design

(a) Desired (b) Undesired

D

q

q

D

CAPACITY DESIGN

Teaching Resources © IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta 13

Lead Plug

Laminated rubber bearing pad

SPECIAL DEVICES AND SYSTEMS

Either isolate or dissipate Base Isolation Vibration Control Active and Passive Visco-elastic dampers used as sliding supports for beams/trusses Tuned Mass Dampers(TMD) Tuned Liquid Dampers(TLD) Hydraulic Actuators Weak links, stoppers etc as inelastic dampers