Civil Engineering Reference
In-Depth Information
Table 6.4
Evolution of seismic design forces in the National Building Code of
Canada
Base shear
formula
Year
Comments
NBC 1941
V
=
CW
NBC
National Building Code; incorporated in
an appendix and was based on concepts
presented in the 1937 U.S. Uniform Building
Code (UBC);
V
=
=
lateral force;
C
varied from
0.02 to 0.05;
W
=
total weight (dead load
+
25% of the snow load).
NBC 1953
V
=
CW
Incorporated into the main text of 1953 NBC;
Inclusion of Canadian seismic zoning map;
and recognition of the infl uence of building
fl exibility;
W
=
total weight (dead load
+
25%
of the design snow load);
C
horizontal force
factor for minimum earthquake load; Zone 1:
C
=
=
0.15/(
N
+
4.5); Zone 2:
C
=
0.30/(
N
+
4.5);
Zone 3:
C
=
0.60/(
N
+
4.5);
N
=
number of
storeys.
NBC 1965
V
=
RCIFSW
R
=
seismic regionalizing factor (values are 0, 1,
2, and 4 for earthquake intensity zones 0, 1,
2, and 3, respectively);
C
=
type of
construction factor (
0.75 for moment
resisting space frame;
=
=
1.25 for non-ductile
structures);
I
=
importance factor (1 or 1.3);
F
=
foundation factor;
S
=
structural fl exibility
factor
=
0.25/(N
+
9);
W
=
total weight (dead
load
+
25% of the design snow load
+
design
live load for storage area).
NBC 1970
V
=
1
/
4
R
(
KCIFW
)
Seismic zoning map was revised;
R
,
I
,
F
,
and
W
are same as NBC 1965;
K
type of
construction factor (values range from 0.67
to 1.33 for buildings);
C
=
=
structural fl exibility
factor
fundamental
period of the structure (0.05
h
n
/
D
1/2
or 0.10
N
);
h
n
=
0.05/T
1/3
≤
0.10;
T
=
=
height of the structure in feet;
D
=
dimension of the building in direction
parallel to seismic force in feet;
N
=
number
of storeys.
NBC 1975
V
=
ASKIFW
I
,
F
, and
W
are same as NBC 1965;
A
=
assigned horizontal design ground
acceleration;
S
=
seismic response factor (0.5/
T
1/3
numerical coeffi cient refl ecting
the infl uence of the type of construction on
the damping, ductility, and (or) energy-
absorption capacity of the structures (values
range from 0.7 to 2 for buildings).
≤
1);
K
=
NBCC 1980
V
=
ASKIFW
No major change.
(
Continued
)
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