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Superstructure : this is the top most part of the bridge which forms a medium or a platform for the movement of the traffic and facilitates its smooth uninterrupted passage over natural/man made barriers like rivers, creeks, roads, railways.
ii.
Substructure : provides a support to the superstructure of the bridge. i.e. Piers & Abutments.
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iii.
Foundation : that part of the bridge in direct contact with ground. Foundation supports the substructure. It transmits the loads received from superstructure and substructure to the ground.
iv.
Bearings : Bearings are provided at the interfaces interfaces of the superstructure and substructure to transmit the loads from superstructure to substructure. The basic function of the bearings are: To transmit all the loads from superstructure to substructure
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To allow the lon gitudinal movement of the superstructure due to thermal expansion & contraction
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To allow for f or the rotation of the superst ructure caused b y dead load and live load deflection.
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Overall Width of Carriageway : is the total width of the carriageway measured perpendicular to the direction.
ii.
Clear Width of Carriageway : is the width of the carriageway between raised kerbs measure perpendicular to the direction of the traffic. Actually it the width of the carriageway within which the vehicular traffic is supposed to move.
iii.
Traffic lanes : the lanes that are marked on the running surface of the bridge and are normally used by traffic.
iv.
Width of Single lane
4.5m
Width of Two Lanes
7.5m
Width of Multiple Lanes
7.5m + 3.5m for every additional lane of traffic
Vertical Clearance – is a minimum vertical distance between the soffit of the superstructure and the topmost surface of the road below. The value depends on the location of the structure, i.e. urban area, expressway.
5L?K@9B?D<9@M BC (LG=EA@ELK@LE= *B>GB?=?@A; The typical superstructure components consist of the following:
Wearing Coat – the top most surface of the bridge deck which resists traffic wear. In general it is a separate layer made of bituminous material, while sometimes it is made of concrete material.
Deck Slab – the deck slab is the physical extension of the roadway across the obstruction to be bridged. In the fig shown above, the deck slab is a reinforced concrete slab. The main
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function of the deck slab is to distribute loads transversely along the bridge cross section. The deck rests on the longitudinal members, girders or webs of the Box girder.
Main Girder – also called longitudinal Girders as those are put along the longitudinal axis of the bridge (in the direction of the traffic). Girders receive load from deck and distribute it longitudinally. Those are designed to resist flexure and shear. The main girders are made of steel plate girders, Reinforced or Prestressed Concrete „I‟/‟T‟ shaped beams, webs of Box Girder, etc.
Cross Girder – also called diaphragms, are bracing members between longitudinal members. They help to resist cross-sectional deformation of the longitudinal members. They also help for the stability of the longitudinal members during construction. The cross girders provided at the end of the longitudinal members (End Diaphragms), receive the loads of the deck from the deck and transfers to the bearings.
Kerb (Curb) – a raised element generally made up of RCC to denote the edge of pavement on the deck.
Parapet – A concrete barrier placed at the outside face of the deck. It is called a railing if made up of steel materials.
Crash Barrier – is a solid concrete barrier placed at the outside face of the deck to safeguard against errant vehicles. Those are more robust and can resist more thrust of vehicle when struck. Those are specifically provided in bridges on flyover & interchanges in urban areas, express way and multi-level bridges.
Median (Central verge) – curb like element put on deck at the central of carriage way width to put a physical barrier to the bi directional traffic movement.
Footpath – a defined portion of the deck slab to allow the pedestrian movement over the bridge. There may be a raised curb like element or may be a small width of the carriageway is separated by crash barrier/parapet on either side.
Expansion Joint – to allow for the movement of the superstructure due to temperature, creep, shrinkage, etc., some gap is required between two spans. But the leakage at this gap leads to reduced durability and disfiguration of the structure below. To resolve this problem and to allow for required movement of the deck an Expansion Joint is provided. Expansion joint makes deck gap leak proof, protects the edges of the slab/girder and also allow smooth passage of traffic from one span to other by bridging the gap.
5L?K@9B?D<9@M BC (LO (@ELK@LE= *B>GB?=?@A; The typical sub-structure components consist of the following:
Bearings – are the vital component of the bridge which transmits the vertical and horizontal loads of the superstructure to the substructure. They also accommodate movements between the superstructure and the substructure due to expansion and contraction. Thus they relieve
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the stresses due to expansion/contraction of the superstructure. All bridge superstructures deflect under loads, so the bearings must be able to accommodate the small rotations at the support
.
Pedestals – A pedestal is a short column under a bearing connected with the pier/abutment cap. It transfers the forces from bearings to pier/abutment.
Pier Cap – A Long Transverse RCC component below the bearing/pedestals provides a platform for the bearings and is connected with the Pier below.
Pier – is a vertical element to support the superstructure span at intermediate points of the bridge. It receives the forces of superstructure through bearings and transfers to the foundation.
Abutment – are the end supports of the bridge to support one end of the first and last span, retain earth of the approach embankments.
Dirt Wall – is a thin wall projecting up from the abutment immediately behind the bearings to retain the soil behind. Apart from the retaining the soil on road side it also supports the approach slab.
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Approach Slab – To compensate for potential differential settlement at the approaches (just behind the abutment), a RCC slab – approach slab is placed for some length behind the abutment. It is typically supported by the abutment at one end and supported by the soil along its length. !
Helps to evenly distribute traffic loads on the soil behind the abutment.
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Minimizes impact to the abutment which can results from differential settlement between the abutment and approach.
Wing Walls – are small retaining walls provided at the end of the abutments to retain the soil filling of the approaches. Wing walls may be right angled with the abutments or splayed at different angle.
Weep Holes – are provided in the abutment stem above the ground level. when the water enters the approach embankment fill, more soil pressure is exerted on the abutment wall. To reduce this pressure, water must be drained out by placing the hopes in the abutment wall.
Drainage Filter – may be used on the back face of abutment wall in order to avoid the fine particles of the back fill material entering the weep holes and eventually clogging them.
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It is very interesting to understand the development the various basic types/shapes of the superstructure. One should select a superstructure which is simplest one for particular need, which gives the simplicity in construction, analysis & design and which gives the good aesthetic look. Various Cross sections options for superstructure are described below.
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This shall be considered as the simplest form of the bridge superstructure. It is simply a thick slab to form an entire width of carriageway. It provides the surface to the traffic at the same time takes all the shear and flexure. Solid slab is considered to be very
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speedy construction, less labor efforts, and comparatively good quality of construction. It is considered that the solid slabs are suitable for spans up to 10m-12m for RCC and upto around 15m for Prestressed Concrete. Broadly solid slabs shall be adopted for the spans which required depth upto 600mm to 700mm. when the thickness of a slab exceeds about 700mm, the cost of carrying the additional self-weight tends to outweigh its virtue of simplicity. This is because of the fact that most of its strength (say flexural capacity) is being utilized to sustain its own weight and hence very little strength remains balance to take the traffic loads.
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76)-,- (1'& For the spans more than 15m, the required depth of solid slab is quite high and it results in excessive
self-weight.
Following the basic principle to keep the tensile fibre stresses within limit, one can remove some of the concrete around the neutral axis and thus reducing the self-weight of slab. To remove the concrete within the slab around its neutral axis, void forms shall be kept before concreting. This type of the slab is called as “Voided Slab”. By introducing voids, the essential simplicity of slab is sacrificed. The cost of voids including the measures need to be taken to hold them steady during concreting and to resist the up-thrust of the wet concrete, is as much as the cost of concrete saved. This also requires greater labor efforts and unit cost of the reinforcement is increased. However voided slab is having the benefit of greater deck efficiency, lower weight leading to economy of the substructure and foundation cost.
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&6U 3)2-,2 For the larger spans, the size of the voids in the voided slab becomes quite high required greater depth of the slab and affects the integrity of the slab. This can be resolves by forming rectangular voids in the slab instead of circular voids. This result in the thin vertical walls connected with top and bottom thin slabs. This is called the “Box Girder”. It is a logical conclusion of the development of the voided slab. The box girder is a voided slab with rectangular voids. The void forms are no more being used for the construction of the box girder, but removable shuttering is used.
The construction of the box girder is bit slow, labor intensive and having modest formwork requirement, clumsy reinforcement detailing and also complex in analysis and designing. The greater advantage of the box girder is slim cross section, reduced self-weight and higher degree of stiffness due to close form shape. It is very much suitable for the spans upto 40m to 50m and for the span having curvature in plan.
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. &,'8 -,*V (1'& ./0, For the medium span ranges from 15m to 35m, or for straight spans, the lateral stiffness due to bottom slab from box girder can be omitted. The removal of soffit slab of box girder results in the web to act as an individual girder connected at top with deck slab. This type of superstructure is called “T beam Girder & Deck slab”. The removal of soffit slab results in the reduction in the self weight of superstructure. For the lateral stability and stiffness of the girder, intermediate cross beams (diaphragms) are provided at suitable intervals.
Such type of superstructure is most suitable for pre-cast construction. Girders can be pre casted and launched in position. Then after, deck slab can be casted in situ.
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/I' -H"F' 'eA-E%"G .%F'@ F-&A'@ "B 7C# B"? eA-?E%Z'D.?-G%E' -..?'.-E'@R 9"? "EI'? -..?'.-E'@L %E @I"A&( H' #A&E%$&%'( H+ B-CE"?@ -@ .%F'G H'&"TW >?@"<)-%" A 8BC; ,$%D<)-%" A 8BE8; F$<$*) A :B7
The variation of modulus of elasticity with time ‘t’ ( which @I"A&( "G&+ H' ?'eA%?'( B"? &"-(%G. -E
'-?&+ -.'S %@ .%F'G H+ W
HS # , - . '
. = ( )
/I' "EI'? ?'&'F-GE $?"$'?E%'@ "B C"GC?'E' -?' W Poisson’ ratio : for uncracked concrete = 0.2
9"? C?-CJ'( C"GC?'E' f a (@E=AA – A@ED9? E=
1:! cc\ #-J'@ (%@E%GCE%"G H'ET''G EI' ?'eA%?'#'GE@ B"? @E?'@@>@E?-%G ?'&-E%"G@I%$@ B"? A@' %G .&"H-& -G-&+@%@ QG"G>&%G'-? @E?ACEA?-& -G-&+@%@S -G( B"? A@' %G EI' F'?%B%C-E%"G "B C?"@@>@'CE%"G@R C
C
B C# aRbbB C#
C
B CJ
B CJ
B C(
B C(
tan Ecm
a
Cc
CAc
C
a
C\
C
CA\
a
Cb
CAb
Note : The use of 0.33f cm for the definition of Ecm is approximate
(a) For Structural Analysis
(b) Parabolic rectangular
(c) Bilinear
59:% H%I ; (@E=AA\A@ED9? E=
9%.R bR`Q-S @I"T@ @CI'#-E%C ?'$?'@'GE-E%"G "B EI' @E?'@@>@E?-%G ? '&-E%"G B"? @E?ACEA?-& -G-&+@%@R 9"? C?"@@ @'CE%"G ('@%.GL EI?'' -&E'?G-E%F' @E?'@@>@E?-%G (%-.?-#@ -?' $?"F%('(W cS $-?-H"&%C ?'CE-G.A&-?L H%&%G'-? -G( @%#$&%B%'( ?'CE-G.A&-?L -@ @I"TG %G 9%. bR` QHS j QCSR /I'@' I-F' H''G C"G@E?ACE'( A@%G. B"&&"T%G. 'eA-E%"G@ .%F'G %G 1:! cc\R 0DEDOB<9K\E=K@D?:L
= ( ) 0≤ ≤ = ≤ ≤
MI'?'L
G f 7O$"G'GE -@ .%F'G %G /-H&' bRc C\ f 8E?-%G -E ?'-CI%G. CI-?-CE'?%@E%C@ @E?'G.EI -@ .%F'G %G /-H&' bRc CA\ f =&E%#-E' @E?-%G -@ .%F'G %G /-H&' bRc H$ # , - . '
C
&9<9?=DE F9D:ED>
Cb f 8E?-%G -E ?'-CI%G. CI-?-CE'?%@E%C@ @E?'G.EI -@ .%F'G %G /-H&' bRcL %R'R -E B C( TI'G ('@%.G F-&A'@ -?' A@'( CAb f =&E%#-E' @E?-%G -@ .%F'G %G /-H&' bRc CAb
B C( $
!
"
&
%
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#
!
$
"
@ 59:% H%J ; (9>G<9C9=F 2=K@D?:L
(9>G<9C9=F E=K@D?:L ]2=C=E C9:% H%J^
-G( B-CE"?@ -?' A@'( E" ('B%G' EI' 'BB'CE%F' I'%.IE "B EI' C"#$?'@@%F' Z"G' -G( 'BB'CE%F' @E?'G.EI ?'@$'CE%F'&+R f aR_
B"? B CJ ≤ 60 MPa
f aR_ – QB CJ – YaSD]aa
B"? Ya h B CJ ≤ 110 MPa
f cRa
B"? B CJ ≤ 60 MPa
f cRa – QB CJ – YaSD\]a
B"? Ya h B CJ ≤ 110 5,-
9"? ('@%.G "B C"GC?'E' @'CE%"GL
=
L
TI'?'L f aRY^ -G( # f cR] B"? *-@%C j 8'%@#%C !"#H%G-E%"G f cR\ B"? 2CC%('GE-& !"#H%G-E%"G
H! # , - . '
HH # , - . '
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c
B CJQ5,-S
8 $J c]
8 !S \a
8 !J \]
8 HS ba
8 HJ b]
8 IS `a
8 IJ `]
8 JS ]a
8 JJ ]]
8 NS Ya
8 NJ Y]
8 PS ^a
8 PJ ^]
8 QS _a
8 QJ _]
8 RS da
5BE>L
\]
ba
b]
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]a
]]
Ya
Y]
^a
^]
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_]
da
d]
caa
B CJ X ca
cRY
cRd
\R\
\R]
\R_
bRa
bRb
bR]
bR^
`Ra
`R`
`R]
`R^
`R_
`Rd
]Ra
B CJ ≤60: 0.259(f CJS B CJ iYaW \R\^&GkcXQB C#Dc\R]Sl
cRc
cRb
cR]
cR^
cRd
\Rc
\Rb
\R]
\RY
\R_
\Rd
bRa
bRc
bR\
bRb
bRb
aR^B CE# B CEJmaRa] %@ aR]g B?-CE%&'
\Ra
\R]
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bR\
bRY
bRd
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\^
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bc
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bb
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bd
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aRY]bQB C#SaRbch\R_
bR`
bR\
bRa
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CI-?-R !"#$R CAH' @E?'G.EI -E \_ (-+@
\
B C#Q5,-S 5'-G V-&A' "B C"GC?'E' CAH' C"#$R @E?'G.EI
b
B CE#Q5,-S 5'-G V-&A' "B -O%-& E'G@%&' @E?'G.EI
`
B CEJLaRa]Q5,-S CI-?-R 2O%-& E'G@%&' @E?'G.EI
]
B CEJLaRd]Q5,-S CI-?-R 2O%-& E'G@%&' @E?'G.EI
Y
7C# Q<,-S
\Db
8'C-GE #"(A&A@ "B '&-@E%C%E+
^
CcQ‰S
_
CAcQ‰S
d
C\Q‰S
bR]
.* .+ .0.0 00. 0. . 00.00 .. 00.00 B"?
B CJiYa5,-
\Ra
\Rc
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\Rb
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bR]
bRb
bRc
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cRd
cR^
cRY
cR]
cR]
cR`
cR_
cR_
cR_
cRd
cRd
\Ra
\Rc
bR]
bRb
bRc
\Rd
\R_
\R^
\RY
B"? B CJiYa5,-
ca
CA\Q‰S
cc
6
B"? B CJiYa5,-
B"? B CJiYa5,-
c\
CbQ‰S
cb
CAbQ‰S
HI # , - . '
H%H%! 2=9?CBEK9?: (@==< /I' #"@E %#$"?E-GE ?'%GB"?C'#'GE $?"$'?E+ E" EI' ('@%.G'? %@ A@A-&&+ EI' CI-?-CE'?%@E%C +%'&( @E?'G.EIL B +JR 1E %@ "HE-%G'( H+ (%F%(%G. EI' CI-?-CE'?%@E%C +%'&( &"-( H+ EI' G"#%G-& C?"@@>@'CE%"G-& -?'- "B EI' H-?R 2&E'?G-E%F'&+L EI' aR\g $?""B @E?'@@LB aR\JL #-+ H' A@'( %G $&-C' "B EI' +%'&( @E?'@@R 9%. `RY %&&A@E?-E'@ E+$%C-& @E?'@@>@E?-%G CA?F'@ B"? ?'%GB"?C'#'GER
@
B E B
+J
B E
B
+J
f B
@
f B
aR\J
aR\J
a
@
AJ
a
(a) Hot rolled HYSD Steel
aR\g
AJ
@
(b) Cold Worked HYSD Steel
Es = slope of linear portion = 200 GPa
59:% H%N ; (@E=AA\(@ED9? -9D:ED> BC 4?\@=?A9B?=F 2=9?CBEK=>=?@
@ Idealised Bilinear Diagram
B E
Factored Idealised Design Bilinear Diagram
B J
Simplified Bilinear Diagram
B +(fB +JD@
a
Factored Simplified Design Bilinear Diagram
B +(D7@
A( f aRd AJ
AJ
@
59:% H%P ; &9<9?=DE (@E=AA\(@ED9? -9D:ED> BC 2=9?CBEK9?: A@==< CBE -=A9:?
9"? ('@%.G $A?$"@'L @%#$&%B%'( H%&%G'-? (%-.?-# -@ .%F'G %G 9%.R bR^ #-+ H' A@'(R @ %@ E-J'G -@ cRc] B"? H-@%C -G( @'%@#%C C"#H%G-E%"GL -G( cRa B"? -CC%('GE-& C"#H%G-E%"G
HJ # , - . '
H%I 16'- *68&)+'.)6+( 9"? 3%#%E@ 8E-E' ;'@%.GL EI' F-?%"A@ &"-( C"#H%G-E%"G@ -?' E" H' C"G@%('?'( B"? =83 j 838 CI'CJ@R /I' C&-A@'@ ('@C?%H'( %G 2GG'O * "B 1:! W Y @I-&& H' ?'B'??'( B"? EI' @-#'R /I' B"&&"T%G. CI-?E @I"T@ EI' $-?E%CA&-? &"-( C"#H%G-E%"G@ E" H' B"&&"T'( B"? F'?%B%C-E%"G "B F-?%"A@ @E?ACEA?-& 'BB'CE@ AG('? =&E%#-E' 3%#%E 8E-E' j 8'?F%C'-H%&%E+ 3%#%E 8E-E'R
41.)8'., 1)8). (.'., ,aL9<9OE9L> (@E=?:@T ]6X=E@LE?9?:b ])?@=E?D< 5D9D@9B?^ 2=C=E=?K= CEB> '??=g &b)2* N
Basic Combination
Table 3.1 column 2,3
Table 3.2 column 2
Accidental Combination
Table 3.1 column 4,5
Table 3.2 column 3
Seismic Combination
Table 3.1 column 6,7
Table 3.2 column 4
H%J 41.)8'., 868,+. 65 2,()(.'+*, 65 *6+*2,., (,*.)6+ G<<.@H)?-%< 1 /I' @E-G(-?( -@@A#$E%"G@ B"? EI' C-&CA&-E%"G "B A&E%#-E' #"#'GE@ "B ?'@%@E-GC' "B - C"GC?'E' @'CE%"G -?' -@ B"&&"T@W %R
,&-G' @'CE%"G@ ?'#-%G $&-G' -BE'? H'G(%G.R
%%R
8E?-%G %G H"G('( ?'%GB"?C'#'GEL TI'EI'? %G E'G@%"G "? C"#$?'@@%"GL %@ EI' @-#' -@ EI' @E?-%G %G EI' C"GC?'E' -E EI' @-#' &'F'&R
%%%R
H%J%$
/'G@%&' @E?'G.EI "B EI' C"GC?'E' %@ %.G"?'(R
(9?:A ` (
!"#$?'@@%"G B-%&A?'@ -?' (-G.'?"A@ %G $?-CE%C' H'C-A@' EI'+ "CCA? @A(('G&+L .%F%G. &%EE&' F%@%H&' T-?G%G. -G( -?' H?%EE&'R /'G@%"G B-%&A?'@L I"T'F'?L -?' $?'C'('( H+ T%(' C?-CJ%G. "B EI' C"GC?'E' -G( I-F' - (ACE%&' CI-?-CE'?R /" 'G@A?' EI-E -&& H'-#@ I-F' -('eA-E' F%@%H&' T-?G%G. HN # , - . '