Cantilever bridge lecture by amanat sir ce 316

E
B
CE 316: Concrete Structures Design Sessional I
PRELIMINARY DESIGN OF THE SUPERSTRUCTURE OF
A
CANTILEVER BRIDGE FOR GRAVITY LOADING
•- ----�
Acommon RC bridge in rural Bangladesh
Multiple Simply Supported Spans
Dr. K.M. Amanat Dept. of Civil Engg. BUET, 2014

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A
•- -----
Multiple Simply Supported Spans
BMD
Advanta1:e
Determinate structure:
No stress due to differential settlement.
Disadvanta1:e
Large magnitude ofbending moment requiring
bigger and heavier section: uneconomic

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B
A
•- -----
Continuous Spans
BMD
Advantage
Magnitude of maximum moment reduced:
Resulting in economic section
Disadvantage
Large bending moment due to uneven/differential
settlement

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A
•- ---�-
Developing the Idea of Cantilever Form
� f
�
f f f f f f f f !
f
A
f f f !
f
A
f f
A
BMD
Point of contraflexure
-• Zero moment
...... Hinge
Advantages of both the simply-supported
and continuous span can be retained
&
Disadvantages can be eliminated by
Inserting structural hingesat some ofthe
points of contraflexure .

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A
•- -----
Developing the Idea of Cantilever Form
Statically indeterminate to 3rd degree. Therefore, Hinges render the structure
determinate:
Thus the problem of large
stress due to settlement is
eliminated.
three hinges are required to make it determinate.
�Hinge�
M • • •
"'wL
"'
24
Bending moment diagram of
indeterminate structure is
retained:
BMD
Thus the
becomes
design section
economic
THREE SPAN
BRIDGE
Statically indeterminate to
znd degree. Therefore,
two hinges are required to
Cantilever span

make it determinate.
/uspended span hinge

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A
•- ------
Possible Cantilever Configurations For Three Span Bridge
No. ofpoints ofcontraflexure = 4, Degree of static indeterminacy= 2
Thus the beam can be made determinate by inserting hingeat any two ofthe four points of
contraflexure.
Therefore, there can be 4C2 =
Four are shown below.....
6 different arrangements of hinges.

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PRELIMINARY DESIGN OF THE SUPERSTRUCTURE OF A
•- -----
Example:
Sebastian Inlet Bridge, Florida, USA
Year of construction: 1965, Total length= 4 72m, Central span = 55m.
Simple spans Cantilever Bridge
Central Span (SSm)
--±��---
End Span
End Span
r 4

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A
•- -----
Example: Sebastian Inlet Bridge, Florida, USA
Cantilever Span Suspended Span Cantilever Span
Halving Joint/ Articulation
End Span

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A
•- ----
Support Details
Bearing Diaphragms

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•- ---�-
Support Details

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•- ---�-
DiaphraKm Details
v
Diaphragms Diaphragm

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•- -----
Components of a Cantilever Brid&:e
Cantilever/
Overhang
Suspended spa�/1,;
Articulation /
alving joint
I
I I
I L
_I
I
I I
I L
_I
Pier
Pile cap .-_�---.--.......
.:
Abutment Footing
Pile
(or Caisson)

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•- -----
Components of a Cantilever Brid&:
e
I
I
I
I
I
I
LJ
�--1
I
I
I
I
I Bearing

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A
•- -----
Neoprane Bearing Pad

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•- -----
Bridge Deck Configurations (AASHTO 2012 Chapter 4)
Table 4.6.2.2.1-1-Common Deck Superstructures Covered in Articles 4.6.2.2.2 and 4.6.2.2.3
T e Of Deck T ical Cross-Section
Cast-in-place concrete slab,
precast concrete slab, steel
grid, glued/spiked panels,
stressed wood
(a)
Closed Steel or Precast Concrete
Boxes
Cast-in-place concrete slab
D
(b)
Open Steel or Precast Concrete
Boxes
Cast-in-place concrete slab
precast concrete deck slab
(c)

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•- -----
Table 4.6.2.2.1-1--Common Deck Superstructures Covered in Articles 4.6.2.2.2 and 4.6.2.2.3
T e Of Deck T ical Cross-Section
Monolithic concrete
I
I
I
I
(d)
Cast-in-Place Concrete Tee Beam Monolithic concrete
(e)
Precast Solid, Voided or Cellular
Concrete Boxes with Shear Keys
Cast-in-place concrete
overlay
DD
(f)

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•- -----
T e OfDeck T ical Cross-Section
Precast Solid Voided, or Cellular
Concrete Box with Shear Keys and
with or without Transverse Post•
Tensioning
Integral concrete
�=1IDIDIDIC�
�
IT
(g)
Precast Concrete Channel Sections
with Shear Keys
overlay
Precast oncrete Double Tee Integral concrete
Section with Shear Keys and with
or without Transverse Post-
Tensioning
(i)

®
A
•- -----
Supporting Components Type Of Deck
Integral concrete
Typical Cross-Section
Precast oncrete Tee Section with
Shear Keys and with or without
Transverse Post-Tensioning I I I
l!
� � �
(J)
Precast oncrete I or Bulb-Tee
Sections
precast concrete J
�
(k)
Wood Beams Cast-in-place concrete or
plank, glued/spiked panels
or stressed wood
J
�
-
-
-
-
-
-
-
-
- -
-
- - =
- .::
.::
.: .: .:
(1)

®
A
•- ---�
Bridge Deck Configurations
Box girder
(Bangabandhu Bridge, Meghna Bridge,
Lalon Shah Bridge, Gabkhan Bridge etc.)
Multiple cell Box girder
(Hanif Flyover, Maghbazar Flyover)
I
)
Spread Box girder
I
D D (Bangladesh China 1st Friendship Bridge)

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•- ----
Bridge Design Items
ef1. Bridge superstructure:
Deck Girders
Diaphragm beams
Railing
Articulation etc.
2.
3.
Bridge Pier
Foundation
Pile cap
Pile (or caisson)
Abutment and wing
Approach road
4.
5.
6.
walls
River training works

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•- ----
Loads on Brid�e (AASHTO 2012. Sec. 3.3.2)
The following permanent and transient loads and forces are
act on a bridge structure:
considered to
Permanent Loads
CR = force effects due to creep
DD = downdraa force
DC= dead load of structural components and nonstructural attachments
DW = dead load of wearing surfaces and utilities
EH = horizontal earth pressure load
EL = miscellaneous locked-in force effects resulting from the construction
process, including jacking apart of cantilevers
ES = earth surcharge load
EV= vertical pressure from dead load ofearth fill
PS= secondary forces from post-tensioning
SH= force effects due to shrinkage
in segmental construction

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•- ----
Transient Loads
BL = blast loading
BR = vehicular braking force
CE= vehicular centrifugal force
CT = vehicular collision force
CV= vessel collision force
EQ = earthquake load
FR = friction load
IC= ice load
IM = vehicular dynamic load allowance
LL = vehicular live load
LS = live load surcharge
PL = pedestrian live load I
SE= force effect due to settlement
TG = force effect due to temperature gradient
TU= force effect due to uniform temperature
WA = water load and stream pressure
WL = wind on live load
WS = wind load on structure
I

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•- ---
DESIGN VEHICULAR LIVE
LOAD
Vehicular live loading on the roadways ofbridges or incidental
structures, designated HL-93, shall consist of a combination
the:
• Design truck or design tandem, and
• Design lane load.
of
Each design lane under consideration shall be occupied by
either the design truck or tandem, coincident with the lane load,
where applicable. The loads shall be assumed to occupy 10.0 ft
transversely within a design lane.

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•- ----
DESIGN TRUCK LOAD
width
l
>1
I
I
I
I
I
I
I
I
I
I
Lane
..
HS20
6 ft
32.0 kips
8.0
(35
kip
kN)
32.0 kip I
I
I
1
ci.s
:)
10 ft
(3 m)
(140 kN) (140 kN)
14
(4.3
ft
m)
14 ft to 30 ft
(4.3 m to 9.1 m)
--
1
Truck load is subjected to
dynamic allowance (impact)

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•- ---�
DESIG
N
TANDE
M
LOA
D
Tandem kips
·
12.5
12.5 kips ·
25 kips= 110
per axle
kN
6 ft
(1.8 m)
Loading
lane
12.5
k
+ips
55kN
-----I12.5
kips
55kN
_
j
..
I
...
.
4 ft �
I
(1.2 m)
Elevation
Top view
TANDE
M
dynamic
load is subjected to
allowance (impact)

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•- -----
DESIGN LANE LOAD
TOP
VIEW
Uniform design load per lane= 640 plf or 9.3 kN/m
SIDE
VIEW
Support, typical
LANE load is NOT subjected to dynamic allowance (impact)

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•- ----
COMBINATION OF LOADS: AASHTO 2012. Sec. 3.4.1
Design load is obtained by combining different basic loads with
appropriate factors for various combination groups
The total factored force effect shall be taken as:
(3.4.1-1)
where:
load modifier specified in Article 1.3 .2
1lt
Q
1
'Yi
force effects from loads
specified
specified herein
load factors in Tables 3.4.1-1 and
3.4.1-2

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•- ----
LIMIT STATES:
Strength I-Basic load combination relating to the normal vehicular
use ofthe bridge without wind.
Strength II-Load combination relating to the use ofthe bridge by Owner-
specified special design vehicles, evaluation permit vehicles, or both
without wind.
Strength III-Load combination relating to the bridge exposed to wind
velocity exceeding 55 mph.
Strength IV-Load combination relating to very high dead load to live
load force effect ratios.
Strength
the bridge
V-Load combination relating to normal vehicular use of
with wind of 55 mph velocity.

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•- ----
LIMIT STATES:
Extreme Event I-Load combination including earthquake. The load
factor for live load YEQ' shall be determined on a project-specific basis.
Extreme Event II-Load combination relating to ice load, collision by vessels
and vehicles, check floods, and certain hydraulic events with
a reduced live
collision load,
load other than that which is part ofthe vehicular
CT. The cases of check floods shall not be combined with
BL, CV, CT, or IC.
Fatigue I-Fatigue and fracture load combination related to infinite
load-induced fatigue life.
Fatigue II-Fatigue and fracture load combination related to finite load-
induced fatigue life.

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•- ----
AASHTO 2012. Sec. 3.4.1
COMBINATION OF LOADS:
LIMIT STATES:
Service I-Load combination the
bridge with a 55 mph wind
relating to the normal operational use
and all loads taken at their nominal
of
values. Also related to deflection control in buried metal structures,
tunnel liner plate, and thermoplastic pipe, to control crack width in reinforced
concrete structures, and for transverse analysisrelating to tension in concrete
segmental girders. This load combination should also be used for the
investigation of slope stability.
Service II-Load combination intended to control yielding of steel
structures and slip ofslip-critical connections due to vehicular live load.
Service III-Load combination for longitudinal analysisrelating to
tension in pre-stressed concrete superstructures with the objective of
crack control and to principal tension in the webs of segmental concrete
girders.
Service IV-Load combination relating only to tension in pre-stressed concrete
columns with the objective of crack control.

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•- ------
AASHTO
Table 3.4.1-1-Load Combinations and Load Factors
2012. Sec. 3.4.1
DC
DD
DW
EH
EV
ES
EL
PS
CR
SH
'Yp
Use One of These at a Time
LL
IM
CE
BR
PL
LS
yEQ
Load
Combination
Limit State
Extreme
Event I
Extreme
Event II
Service I
ws
-
WA
1.00
WL
-
FR
1.00
TG SE BL
-
IC
-
CT
-
CV
-
EQ
1.00
TU
- - -
0.50 1.00 1.00 - - 1.00 1.00 1.00 1.00
- - - -
"(p
1.00 1.00 1.00 0.3
0
-
-
0.7
0
-
1.0 1.00 1.00/1.20 - -
- - -
'tta "(SE
-
-
-
-
-
-
-
-
-
-
-
-
Service II
Service ill
Service IV
1.00
1.00
1.00
1.30
0.80
-
1.00
1.00
1.00
-
-
-
1.00
1.00
1.00
1.00/1.20
1.00/1.20
1.00/1.20
-
'YTG
-
-
'YSE
1.0
-
-
-
- - - - - - -
Fatigue I-
LL,IM &
CE
only
Fatigue II-
LL,IM&CE
only
1.50 -
- - - -
- -
- - - - - - - -
-
0.75 - -

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•- -----
2012. Sec. 3.4.1
COMBINATION OF LOADS: AASHTO
Table 3.4.1-1-Load Combinations and Load Factors
DC
DD
DW
EH
EV
ES
EL
PS
CR
SH
'Y
p
Use One of These at a Time
L
L
IM
CE
BR
PL
LS
1.75
Load
Combination
Limit State
Strength I
(unless noted)
Strength II
Strength III
ws
-
WA
1.00
WL
-
FR
1.00
TU
0.50/1.20
TG SE BL
-
JC
-
CT
-
CV
-
EQ
-
'tto "{S
E
1.35
-
1.00
1.00
-
1.4
0
-
0.4
0
1.00
1.00
0.50/1.20
0.50/1.20
-
-
-
-
-
-
-
-
-
-
-
-
'Y
TG
'Y
TG
'
Y
o
"
{
p
'YSE
'YSE
Strength IV
Strength V
-
1.35
1.00
1.00
1.00
1.00
0.50/1.20
0.50/1.20
-
'YSE
-
-
-
-
-
-
-
-
-
1.0
-
'Y
TG
-
-
'
Y
o
'
Y
p
Stren&:th-1 Combination:
'Yp(Dl) + 'Yp(DW) + 1.75(LL)(1+/M/100)Truck/Tandem + 1.75(LL)Lane+ 1.75(PL)

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•- -----
AASHTO
2012. Sec. 3.4.1
Table 3.4.1-2-Load Factors for Permanent Loads, 'Yp
Load Factor
Type ofLoad, Foundation Type, and
Method Used to Calculate Downdrag
DC: Component and Attachments
DC: Strength IV only
Maximum
1.25
1.50
1.4
1.05
1.25
1.50
Minimum
0.90
0.90
0.25
0.30
0.35
0.65
DD: Downdrag Piles, a Tomlinson Method
Piles, A Method
Drilled shafts, O'Neill and Reese (1999) Method
DW: Wearing Surfaces and Utilities
EH: Horizontal Earth Pressure
•
•
•
EL:
1.50
L35
L35
LO
O
0.90
0.90
N/A
LO
O
Active
At-Rest
AEP for anchored walls
Locked-in Construction Stresses
Stren�th-1 Combination:
Yp(Dl) + Yp(DW) + 1.75(LL)(1+/M/100)Truck/Tandem + 1.75(LL)Lane+ 1.75(PL)
= 1.25(Dl) + 1.S(DW) + 1.75(LL)(1+/M/100)Truck/Tandem + 1.75(LL)Lane+ 1.75(PL)

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•- ----
Dynamic Effect ofLive Load (for Truck or Tandem)
IMPACT ALLOWANCE
D The term impact as ordinarily used in structural design refers to the
dynamic effect of a suddenly applied load.
In the building ofa structure, the materials are added slowly; people entering
a buildingare also considered a gradual loading. Dead loads are static loads;
i.e., they have no effect other than weight.
Live loads may be either static or they may have a dynamic effect.Any live
load that can have a dynamic effect should be increased by an impact factor.
While a dynamic analysis of a structure could be made, such a procedure is
unnecessary in ordinary design. Thus, empirical formulas and impact factors
are usuallyused.
For highway bridge design, impact is always to be considered. AASHTO
prescribes empirically that the static effect of live load be multiplied by a factor
(1 + IM/100)
to take into account the dynamiceffect of live load.
D
D
D

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•- ---�-
Dynamic Effect ofLive Load (for Truck or Tandem)
IMPACT ALLOWANCE
Load Allowance, IM
Table 3.6.2.1-1-Dynamic
IM
75%
Component
Deck Joints-All Limit
I I I
States
All Other Components:
•
•
The
15%
33%
Fatigue and Fracture Limit State
All Other Limit States
dynamic load allowance shall not be applied to pedestrian loads or to
the design lane load.

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•- ----
COMBINATION OF LOADS
For the present case
DC= Self weight ofstructural components
DW= Weight ofwearing course
LL = Lane load with vehicle or tandem
IM= Impact effect ofvehicle or tandem load
PL = Pedestrian load
'Yp(DC) + 'Yp(DW) + 1.75(LL)(1+/M/100)Truck/Tandem + 1.75(LL)Lane+ 1.75(PL)
= 1.25(DC) + 1.S(DW) + 1.75(LL)(1+/M/100)Truck/Tandem + 1.75(LL)Lane+ 1.75(PL)

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•-
APPLICATION
----
OF BRIDGE LIVE
LOADS
1.
2.
3.
Standard lane width: 12 ft, Load occupies 10 ft width across lane.
Fractional lanes not permitted.
For total bridge load: lane loads may be reduced
No reduction
as follows:
1
3
4
or 2 lane bridge:
lanes: Abutment load,
90
75
percent
percent
Pier load etc.
or more lanes:

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•-
H
---�
gap, Be
----i
rExpansion
T.n.
A
l
H
A
d
Ls
H
::r:
:� l�
g
�z,...,3'
� � �2,...,3ft
.
.
�
- - -
- - -
L
e
L
e
L
e
L
e
-
L
E
L
M
L
Assumed
L
E
- -
Total span:
End span: Middle
span: Suspended
span: Cantilever
span:
L
LE
L
M
Ls
Le
Relations
LM = 1.4LE
Le= 0.3 Ls
H > 0.07Ls (TABLE 2.s.2.6.3-1, AASHTO 2012)

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•-
Sidewalk
---�
Railin
Roadway width
Wearing course
..
.0
..
I
M
12 i
in.
t
6--9
1%- 2% slope
t
H
3ft
---- --
Haunch
l.w
:
s
Girde Diaphragm
Assume
bw = H/4 -- H/3 > 7"
18" ts: S/12
>
Typical section A-A

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•-
PER STUDENT
-----
DESIGN DATA FOR STUDENTS
DATA
Student
SI
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
Total Student
SI
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
Total Student
SI
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
Total
fc' fc' (ksi)
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
Span, L ft
25
0
25
3
25
6
25
9
26
2
26
5
26
8
27
1
27
4
27
7
28
0
28
3
286
28
Span, L ft
31
9
32
2
32
5
32
8
33
1
33
4
33
7
34
0
343
34
6
349
35
2
35
5
35
8
Span, L ft
38
8
39
1
39
4
39
7
40
0
40
3
40
6
40
9
41
2
41
5
41
8
42
1
42
4
fc' (ksi) fy (ksi)
fy (ksi)
7
2
7
2
60
6
0
60
6
0
6
0
6
0
60
6
0
6
0
6
0
60
6
0
60
6
fy (ksi)
60
6
0
6
0
6
0
6
0
7
2
7
2
7
2
7
2
7
2
7
2
7
2
72
7
2
(ksi)
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
4
4
4
4
4
4
4
4
4
4
4
4
7
2
7
2
7
2
7
2
7
2
7
2
7
2
7
2
7
2
7
2
7
2
6
0
6
- -

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•- ----
DESIGN DATA FOR STUDENTS
COMMON DATA
Wearing course,
DESIGN CODE
AASHTO LRFD BRIDGE DESIGN
wwc = 30 psf
2012
6Tu
SPECIFICATIONS, ED.
Width ofside walk= 3'-6"
Lane width
Sec-A
14'
Sec-B
13'
Sec-C
12'
Number oflanes = 2
1.5", Slab: 1.0"
Concrete clear cover = Beam
Girder depth
HP = 2.0H for
at pier
L < 350',
= 1.5H for L > 350'

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•- -----
DECK SLAB DESIGN:
DEAD
LOA
D Distribution steel
(parallel to traffic)
Main slab steel
(perpendicular to traffic)
Deck slab is assumed as
a continuous beam
spanning over bridge
girders. The bridge
girders are assumed as
rigid continuous support
Assume a unit width of
slab strip.
s, ft s, ft
+
_w_52
wsw = slab = t/12x 150#/' psf
selfweight, (DC)
- 10
wwc = wearing course, (DW) psf
Mvc = wsw x S2/10 lb-ft
Mvw = wwc x S2/10 lb-ft

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SLAB DESIGN: VEHICLE LOAD
•
DEC
-
K
[
-----
Distribution
steel
Main
steel
Design section
-:on face of girder
]
[ ]
lr-,J
�
u,
• •a•a•a•a�a•a•--a•a•a•a•a�-•1
Y,
,aFa•a•a•a a•A•a•a•�•a•a•a
I/
•
v
-------------
--
1------------
---
-------------
--
--
-
-
- -
-
-
-�
-
--
-
s
s s
16k 16k
f i
6
'
;g
;
;g;
-
MLL
;g
;
'.J
h +MLL
Detailed analysis can be performed based on influence line to
determine the maximum effect.
Alternatively, Table A4-1 in AppendixA4 ofAASHTO 2012 can be used.

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•
DEC
-
K SLAB DESIGN: VEHICLE
LOAD
CANTILEVER BRIDGE FOR GRAVITY
LOADING ----
Table A4-1 in AppendixA4 ofAASHTO 2012, page 4-98
ImportantAssumptions...
D Multiple presence factors and the dynamic load allowance are included in
the tabulated values.
The moments are applicable for decks supported on at least three girders and
having a width of not less than 14.0 ft between the centerlines of the exterior
girders.
For each combination of girder spacing and number of girders, the
following two cases of overhang width were considered:
D
D
• Minimum total overhang width of 21.0 in. measured from the center of
the exterior girder, and
Maximum total overhang width equal to the smaller of 0.62 5 times the girder
spacing and 6.0 ft. Arailing system width of 21.0 in. was used to determine
the clear overhang width. For other widths of railing systems, the difference in
the moments in the interior regions ofthe deck is expected to be within the
acceptable limits for practical design. The moments do not apply to the deck
overhangs and the adjacent regions ofthe deck that need to be designed taking
into account the provisions ofArticle A13.4.1.
•

@
A
•- -----
DECK SLAB DESIGN: VEHICLE
LOAD
4-98
AASHTO LRFD BRIDGE DESIGN SPECIFICATIONS
Table A4-l-Maximum Live Load Moments per Unit Width, kip-ft/ft
Negative Moment
Distance from CL of Girder to Design Section for Negative Moment
Positive
Moment
5.21
5.32
5.44
5.56
5.69
5.83
5.99
6.14
6.29
6.44
6.59
6.74
6.89
7.03
7.17
7.32
s 0.0 in.
5.98
6.13
6.26
6.38
6.48
6.58
6.66
6.74
6.81
6.87
7.15
7.51
7.85
8.19
8.52
8.83
3 in.
5.17
5.31
5.43
5.54
5.65
5.74
5.82
5.90
5.97
6.03
6.31
6.65
6.99
7.32
7.64
7.95
6 in.
4.36
4.49
4.61
4.71
4.81
4.90
4.98
5.06
5.13
5.19
5.46
5.80
6.13
6.45
6.77
7.08
9 in.
3.56
3.68
3.78
3.88
3.98
4.06
4.14
4.22
4.28
4.40
4.66
4.94
5.26
5.58
5.89
6.20
12 in.
2.84
2.96
3.15
3.30
3.43
3.53
3.61
3.67
3.71
3.82
4.04
4.21
4.41
4.71
5.02
5.32
24 in.
1.37
1.51
1.72
1.94
2.16
2.37
2.58
2.79
3.00
3.20
3.39
3.58
3.77
3.96
4.15
4.34
18 in.
1.63
1.65
1.88
2.21
2.49
2.74
2.96
3.15
3.31
3.47
3.68
3.89
4.09
4.29
4.48
4.68
7'
7'
7'
7'
8'
8'
8'
8'
9'
9'
9'
9'
10'
10'
10'
1
O'
--0"
-3"
-6"
-9"
--0"
-3"
-6"
-9"
--0"
-3"
-6"
-9"
--0"
-3"
-6"
-9"

@
DESIGN: VEHICLE LOAD
•
DEC
-
K
---�
SLA
B
Distribution steel
(parallel to traffic)
Main slab steel
(perpendicular to traffic)
s s s
General Load Combination
1.25(DC) + 1.5(DW) + 1.75(LL)(1+/M/100)Truck/Tandem + 1.75(LL)Lane+ 1.75(PL)
Design slab moment, M = 1.25 Mnc + 1.5 Mnw + 1.75 Mrr [ �
MsTRENGTu]
Where Mrr is the live load slab moment from Table A4-1 which includes the
impact effect.
MsERVICE = Mnc + Mnw + Mrr [ required for crack control calculations]

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