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Design of Seismic-Resistant Steel
Building Structures
Prepared by:Michael D. EngelhardtUniversity of Texas at Austin
with the support of theAmerican Institute of Steel Construction.
Version 1 - March 2007
2. Moment Resisting Frames
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M V
Possible Plastic Hinge Locations
Beam(Flexural Yielding)
Panel Zone(Shear Yielding)
Column(Flexural & Axial
Yielding)
Design of Seismic-Resistant Steel
Building Structures
Prepared by:Michael D. EngelhardtUniversity of Texas at Austin
with the support of theAmerican Institute of Steel Construction.
Version 1 - March 2007
3. Concentrically Braced Frames
Types of CBFs
Single Diagonal Inverted V- Bracing V- Bracing
X- Bracing Two Story X- Bracing Chevron Bracing
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Design of Seismic-Resistant Steel
Building Structures
Prepared by:Michael D. EngelhardtUniversity of Texas at Austin
with the support of theAmerican Institute of Steel Construction.
Version 1 - March 2007
4. Eccentrically Braced Frames
e
e
Link
Link
e
e
Link
Link
Some possible bracing arrangement for EBFS
e e e e
ee
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M
V
P
Link Behavior: Forces in Links
e e
M
V
P
15.6 Diagonal Brace and Beam Outside of Link
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Inelastic Response of EBFs
Lateral Stability
The elevator shafts provide lateral stability to the structural steel frame of the building.
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Type 1a – torsional irregularity Type 1b – extreme torsional irregularity
Type 2 – reentrant corner irregularity
Type 3 – diaphragm discontinuity irregularity
Type 4 – out-of-plane offsets irregularity
Type 5 – nonparallel systems irregularity
Horizontal Structural Irregularities (ASCE Table 12.3-1)
A B
2
21 BAB
.
A B
2
41 BAB
.
b
a
cd
d150ca150b . and .
ba
d
c
or . da50cb
Vertical lateral force-resisting elements not parallel to major orthogonal axes of the seismic force-resisting system
Effective diaphragm stiffness changes > 50% from one story to next
1st floor plan (ground)
Typical floor plan
Vertical Structural Irregularities(ASCE Table 12.3-2)
Type 1a – stiffness-soft story irregularity
Type 1b – stiffness-extreme soft story irregularity
Type 2 – weight (mass) irregularity
Type 3 – vertical geometric irregularity
Type 4 – in-plane discontinuity of lateral force-resisting system
Type 5a, 5b– weak story, extreme weak story
3
kkk800kk700k 3i2i1i
i1ii
.or .
ik
1ik
2ik
3ik
3
kkk700kk600k 3i2i1i
i1ii
.or .
ik
1ik
2ik
3ik
im1im
1im
1ii1ii m501mm501m .or .
a
b
b301a .
iV1iV 1ii V80V .
1ii V650V .
(5a)
(5b)
Story Shear
n
xiix FV
Vx = story shear at level x.Fi = summation of horizontal forces above level x.
nF
1F
iFLevel x=5
8
5i5678i5 FFFFFV
8F
7F
6F
5F
Horizontal Distribution of Story Shear – Rigid Diaphragms
k1x
k2x
k3x
k4x
Vx1
Vx
Vx2
Vx3
Vx4
xn
ixi
xx V
k
kV
1
11
For resisting elements along line 1:
Distribution of Story Shear – Flexible Diaphragms
yn
iyi
yy V
A
AV
1
11
For resisting elements along line 1:(Ai is the tributary area of each line of lateral-load resistance)
Vy1
Vy
Vy2 Vy3 Vy4 Vy5 Vy6 Vy7
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Inherent and Accidental Torsion (Rigid Diaphragms)
• Inherent Torsion(12.8.4.1) – consider distance between center of mass and center of rigidity at each floor level. Compute torsional moment, Mt for each level.
• Accidental Torsion (12.8.4.2) - Buildings with rigid diaphragms, consider moving in both directions the actual location of center of mass a distance equal to 5% of the building dimension perpendicular to seismic forces. Calculate accidental torsional moment, Mta.
Center of Mass and Center of Rigidity (Stiffness)
C.R.
C.M.
Amplification of Accidental Torsional Moment
• Dynamic torsional amplification factor Ax
(12.8.4.3) – for buildings with plan structural irregularities 1a or 1b (seismic design categories C,D, E, or F), torsional irregularity shall be accounted by multiplying the accidental torsional moment Mta at each floor level times the factor:
2
0321
A
BAavg
2
avgx
.
.max
AB
