Structural Steel Design

63 Pages·2017·2.34 MB·English

Structural Steel
Design
by Rafael Sabelli, S.E.
Disclaimer
Instructional Material Complementing FEMA 1051, Design Examples
Part 1: Background/Theoretical
• Context in Provisions
• Steel behavior
• Reference standards and design strength
• Moment resisting frames
• Braced frames
• Other topics
• Summary
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Steel Design: Context in
Provisions
• Design basis: Strength limit state
• Using the 2015 NEHRP Recommended Provisions, Refer to
ASCE 7 2016:
– Chap. 11: Seismic Design Criteria
– Chap. 12: Seismic Design Requirements (Buildings)
– Chap. 13: Nonstructural components
– Chap. 14: Design of steel structures
• Refers to AISC Specification (AISC 360-16)
• Refers to AISC Seismic (AISC 341-16)
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Seismic Resisting Systems
• Unbraced Frames
• Connections are:
– Fully Restrained Moment-resisting
– Partially Restrained Moment-resisting
• Seismic classes are:
– Special Moment Frames
– Intermediate Moment Frames
– Ordinary Moment Frames
– Systems not specifically detailed for seismic response
• Braced Frames
• Ordinary Concentric Braced Frames
• Special Concentric Braced Frames
• Eccentrically Braced Frames
• Buckling Restrained Braced Frames
• Special Plate Shear Walls
• Systems not specifically detailed for seismic response
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Monotonic Stress-Strain Behavior
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Plastic Hinge Formation
Plastic
hinge in
beam
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Behavior Modes For Beams
Moment
strain hardening
B
M D J idealized behavior
p E
F
H
K
C
inelastic LTB
A G
M
r
I
elastic LTB
L
M
O
Deflection
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Flexural Ductility of Steel Members
Practical Limits
• Lateral torsional buckling
– Provide sufficient lateral or torsional
bracing
• Local buckling
– Limit width-to-thickness ratios for
compression elements
• Fracture
– Avoid by proper detailing to allow inelastic
strain
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Lateral Torsional Buckling
Resisting
u
moment
E
A
B L
M
p

buckling
M
y with
strain-
hardening inelastic buckling
C
M
e
D
elastic buckling
0
Laterally unbraced length
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Local Buckling
b
Classical plate buckling solution:
2
k E
  
t
cr y
2 2
12(1  )(b / t)
Substituting = 0.3 and rearranging:
b kE
 0.95
t F
y
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