Civil Engineering Reference
In-Depth Information
X
i
g
i
Q
i
'
R
n
¼R
r
ð
3
:
30
Þ
in which for loads for which a maximum value of
g
i
is appropriate
i
¼
D
R
I
0
:
95
ð
3
:
31
Þ
and for loads for which a minimum value of
g
i
is appropriate
1
D
R
I
1
i
¼
:
0
ð
3
:
32
Þ
where
i
is the load modifier, which is a factor relating to ductility, redun-
dancy, and operational importance;
D
is a factor relating to ductility;
R
is a
factor relating to redundancy;
I
is a factor relating to operational impor-
ification;
Q
i
are force effects from loads;
f
is resistance factor;
R
n
is the
nominal resistance; and
R
r
is the factored resistance (
R
n
). For service
and extreme event limit states, resistance factors shall be taken as 1.0, except
for bolts. According to AASHTO [1.23], the limit states are intended to pro-
vide a buildable, serviceable bridge, capable of safely carrying design loads
for a specified lifetime. The resistances of components and connections
can be determined on the basis of inelastic behavior, although the force
effects are determined using elastic analysis. Equation
(3.30)
is the basis of
LRFD methodology. Assign resistance factor
f¼
1.0 to all nonstrength
limit states. Components and connections of a bridge shall satisfy Equa-
tion
(3.30)
for the applicable combinations of factored extreme force effects
as specified at each of the limit states denoted as STRENGTH I, which is
basic load combinations related to the normal vehicular use of the bridge
without wind; STRENGTH II, which is load combinations related to
the use of the bridge by owner-specified special design vehicles, evaluation
permit vehicles, or both without wind; STRENGTH III, which is load
combinations related to the bridge exposed to wind velocity exceeding
90 km/h; STRENGTH IV, which is load combination related to very high
dead load to live load force effect ratios; STRENGTH V, which is
load combination related to normal vehicular use of the bridge with wind
of 90 km/h velocity; EXTREME EVENT V, which is load combination
including earthquake; EXTREME EVENT II, which is load combination
related to ice load, collision by vessels and vehicles, and certain hydraulic
events with a reduced live load; SERVICE I, which is load combina-
tion related to the normal operational use of the bridge with a 90 km/h,
deflection control in buried metal structures, tunnel liner plate, and slope
'
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