CE 496 B

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Nov 16, 2013 (3 years and 9 months ago)

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CE
496 B

Structural Design III

Spring 2011


Howard
Lum

Seismic Design Criteria


California Building Code (CBC) 2010


ASCE 7
-
05 Minimum Load Requirements for
Buildings and Other Structures


AISC 341
-
05 Seismic Design for Steel Buildings


American Concrete Institute (ACI 318
-
08)
Building Code Requirements for Structural
Concrete (Chapter 21)


Site Specific Geotechnical Report



Seismic Design


Seismic Accelerations
-

S
DS

and S
D1


Occupancy Category (OC) per CBC Table
1604.5 (our project
-

OC II)


Importance Factor I (our project, I=1.0)


OC and S
DS

and S
D1

-

determine Seismic Design
Category (SDC) per CBC Sect. 1613.5.6


SDC is used in:


Lateral load system selection


Seismic load factors in load combination


Allowable seismic drifts


Seismic structural detailing




Seismic Design Category (SDC)


Reference: CBC Tables 1613.5.6

Dynamics of Structure


Single Degree of Freedom System:


Lumped mass
-

m


Single damping
-

c (5% typical)


Linear Stiffness
-

k


Period
-

T = 2
π

√m/k


Site Specific Response Spectrum

Earthquake Response Spectrum (ASCE 11.4
-
1)

Short)

S
DS

S
D1

T
L

T
S

T
0

Seismicity

Ss in g

S
1
in g

0.52 g

LB Response Spectrum (2005)

Use USGS data for current project

PGA

Tohoku Earthquake March 2011

PGA=2.70 g

Steel Properties

Fy

Fu

Seismic Design Methods


ASCE Table 12.6
-
1 provides 3 methods


Equivalent Lateral Force (ASCE 12.8)


Base shear static analysis


Lumped Mass at each level


Orthogonal directions of analysis

(transverse & longitudinal)


Modal Response Spectrum Analysis (ASCE 12.9)


Linear elastic dynamic analysis


Seismic Response History Analysis (ASCE Ch.16)


Non
-
linear dynamic analysis using time histories



Vertical distribution of Forces


Reference: ASCE 12.8.3


F
x

= C
vx

* V


where C
vx

= w
x
h
x
k
/∑w
i
h
i
k





w
1

V=F
1
+F
2

F
1 (upper deck)

F
2 (pipe support deck)

h
i

w
2

Horizontal Truss as Diaphragm

Seismic Load Design


Strength Design (12.4.2.3) to ensure adequate
capacity


(1.2 + 0.2 S
DS
)D +

*Q
E
+ 0.5L


(0.9


0.2 S
DS
)D +

*Q
E


Drift Control (12.8.6) to limit content damage and
maintain building separation

Steel Structural Systems


Moment Frame



Concentric Braced Frame




Eccentric Braced Frame

Design of beam
-
column in a moment
frame


Combined Axial & Bending:


Moment resisting frames


Axial Force:


Vertical gravity load +
seismic overturning forces


Moment and Shear:


Lateral loads

AISC Equations H1
-
1a & H1
-
1b

REQUIRED CAPACITY


P
r


P
c =


Pn


M
rx


M
cx =

Mn
x



M
ry


M
cy =

Mn
y

2
.
0


0
.
1
9
8












c
r
cy
ry
cx
rx
c
r
P
P
for
M
M
M
M
P
P
2
.
0


0
.
1
2












c
r
cy
ry
cx
rx
c
r
P
P
for
M
M
M
M
P
P
Large Axial Compression (>= 20%):

Small Axial Compression (< 20%):

Dynamic Analysis


Modal analysis


linear elastic response spectrum






Dynamic Analysis


Time History


Non
-
linear system

Seismic Retrofit Example

Base Isolators

24

Example


Landslide Protection

Before

After

Example


Pumping Plant
Seismic
Upgrade


Hinds Pumping Plant

Eagle Mountain
Pumping Plant

Example


Discharge
Pipelines Seismic Upgrade

Earthquake Structural Failure