challanges made for construction of bridge in hilly areas
Design of t beam bridge using wsm(2)
1. SUBMITED BY- SUBMITED TO-ANKIT
SINGH DR. S.N. SACHDEVA
M.TECH (TRANSPORTATION ENGINEERING) SECTION HEAD (TRANSPORTATION ENGINEERING)
ROLL NUMBER- 3140715 DEPARTMENT OF CIVIL ENGINEERING
NIT KURUKSHETRA NIT KURUKSHETRA
2. What is bridge?
A structure which provides a passage over a gap
without closing the opening which is beneath that gap.
The passage may be due to railway , roadway , canal &
natural river etc.
Initially the naturally available materials such as stone
and timber were extensively used for bridges but now
days artificial materials such as cement concrete &
steel are utilized more in the construction of bridge.
4. History of bridge in india.
During the king “harshavardhna” or even before him
india appears to have a good highway system & such
highways had a number of bridge.
“firoze shah” who ruled the delhi in mid 14th century
built a number of canal & bridges.
“portuguese” in 16th and 17th century built many old
arch masonary bridges in “goa”.
One of oldest stone slab bridge still in use across the
river “cauvery” at “srirangapatnam” bulit by “tippu
sultan”.
6. A number of cable stayed bridges has been built in
india in past two decades. The major one is
“vidhyasagar sethu” across “hooghly” at “kolkata” &
“nalini bridge” on river “jamuna” at “allahabad”.
Inidian railways build a number of large steel arch
bridge in “j & k”.
BRO has erceted a cable stayed bridge in early part of
this milleium which is claimed to be only bridge of the
type at highest altitude in the world at the time of
construction.
ECONOMY IN BRIDGE CONSTRUCTION
Can be achived by using proper materials , effective
supervission & economic method of construction etc.
7. Planning of a bridge
There are few steps in planning of a bridge
Study the need for the bridge
Assess traffic requirement
Location study
Study of alternatives
Short listing feasible alternatives
Developing plans for alternatives including materials etc
preliminary design and costing
Evaluation of alternative , risk analysis and final choice
Finding resources , detailed survey & design
Implementation of design , fixing agency, construction and
commissioning, preparing estimates.
8. Site selection of bridge
Depends upon
Foundations conditions
Clearance requirements
Length of the bridge
Width of the bridge
Live load on the bridge
Initial cost
Operation and maintenance
appearance
9. Classification of bridge
A single construction of bridge can be classified in many
ways but we have a general classification of bridge.
MASONARY ARCH BRIDGE
Probably first category of bridge to be involved.
Aesthetically superior to slab bridges.
Consist of a arch shape slab supported on two apposite wall & it was
adopted earlier for small of 3 to 15m in masonry & extended up to 519m in
steel & 305m in concrete has been built in the world.
PIPE CULVERT
Consist of a pipe barrel under the embankment with protection works at
the entry and exit.
It is suitable for cross drainage flow on relatively flat terrain & in this
discharge is limited & it has negligible maintenance.
11. SLAB BRIDGE
Simplest type of construction.
Adopted for small bridges and culverts.
Span is between 10-20m.
Concrete slab cast monolithically over longitudinal girder.
No. of longitudinal girders depends upon the width of road.
PLATE GIRDER BRIDGE
Span ranges 10 to 60m.
Can be extending up to 250m in continuous construction.
TRUSS BRIDGE
Span 30 to 375m in simply supported case.
Span 30 to 550m in cantilever combination ca
13. SUSPENSSION BRIDGE
Made up of high tensile steel cables strung in form of a catenary to which
the deck is attached by steel suspenders which are made up of steel
rods/members/cables.
Deck can be of timber , concrete or steel spanning across the stiffening
girders transmitting loads to suspenders.
CABLE STAYED BRIDGE
Similar to suspenssion bridge except that there will be no suspenders in the
cable stayed bridges .
A number of cables are streched from support tower directly connected the
decking.
OTHER IMPORTANT CLASSIFICATION OF BRIDGE
Based upon type of structural arrangement.
I-girder bridge
Plate girder bridge
15. truss girder bridge
Suspenssion bridge
Based upon structural action or nature of superstructure action
Simply supported span bridge
Continuous span bridge
Cantilever bridge
Arch bridge
Rigid frame bridge
Based upon type of connections
Riveted bridge
Welded bridge
Bolted bridge
Pinned bridge
16. Based upon floor action
Deck type bridge
Through type bridge
Semi –through type bridge or pony bridge
Double deck bridge-used in rail cum road bridge
Based upon movement of structural parts of the bridge
Fixed(permanent) bridge
Movable bridge
can opened either horizontally or vetically so as allow the river or channel
traffic to pass.
Based upon purpose of bridge
Road bridge
Railway bridge
Padestrain bridge
17. Based upon loading
Irc class aa loading bridge
Irc class a loading bridge
Irc class b bridge
Base upon span length
Culver – up to span length 6m
Minor bridge – up to span length 6 to 30m.
Major bridge – up to span length over 30m.
LOAD FOR DESIGN OF BRIDGE
1. Dead load
Aggregate weight of complete structure elements such as deck, wearing
coat, parapets, stiffeners and utilities.
It does not changes its direction and magnitude with respect to the passage
of time.
18. 2. LIVE LOAD
Includes vehicle live load That are moving on the bridge.
IRC has categorized standards of vehicle live load as under three
following category which is-
(a) IRC CLASS AA LOADING
Treated as heavy loading and all NH & SH and industrial areas’s
bridge are designed for only IRC class AA loading.
If a bridge designed for IRC class AA loading then it will
automatically satisfied IRC class A & class B loading.
It has two pattern of loading
(i) tracked type (ii) wheeled type
(b) IRC CLASS A LOADING
Generally Treated as standard loading for permanent bridges.
Having eight axles with a total length of 25m.
21. IRC CLASS B LOADING
Used for temporary bridges.
It is a light loading as compard to all other loading.
CLASS 70R LOADING
Not used in our country it is used only in US.
3.Impact load
It is account for the dynamic effects of sudden loading
of a vehicle on bridge structure.
It is calculated by multiplying the live load with an
impact factor.
The impact factor is calculated as the IRC-6 suggested
which are discussed below.
22.
23. Impact factor for IRC CLASS A loading
If=A/(B+L)
Where If=Impact factor
A=constant( 4.5 for RCC bridge & 9.0 for STEEL bridge)
B=constant (6.0 for RCC bridge & 13.5 for STEEL bridge)
L= effective span
Impact factor IRC CLASS AA loading & CLASS 70R loading
for span < 9m
(a) Tracked vehicle- 25% for span upto 5m & reducing to 10% for span
upto 9m.
(b) Wheeled vehicle-25% for span upto 9m.
for span > 9m
(a) Tracked vehicle-for RCC bridge 10% upto 40m & as per graph for span
>40m . For steel bridge 10% for all span.
(b) Wheeled vehicle-for RCC bridge 25% upto 12m & as per graph for
span >12m. For steel bridges 25% for span upto 23m & as per graph for
span > 23m.
24.
25. 4. Centrifugal force
consider for bridge constructed on horizontal curve.
Considered to act at a height of 1.2m above the level of carriage way.
C=WV2
127 R
Where c=centrifugal force in KN
w=live in KN
v=speed of vehicle in KMPH
R= radius of horizontal curve in M.
5.Wind load
Assumed as horizontal forces on an area which are-
For DECK structure- area of floor slab and railing
For a through or half through structure- area of elevation of the windward
tress flows half the area of elevation above the deck slab.
Considered as acting at 15m above the roadway and have the following
values
highway ordinary bridges – 3.0 KN per meter
highway bridges carrying framework- 4.5 KN per meter.
26. 6. Longitudinal forces
Forces result from vehicle braking or acceletrating while travelling on
bridge.
As the vehicle brakes the load of the vehicle is transferred from its
wheels to bridge deck.
IRC specifies a longitudinal forces of 20% is appropraite of live load
and the force is applied at 1.2m above the level of deck.
7.Seismic forces
Depends upon geographical location of the bridge.
These are the temparory forces act for the short duration. An
earthquake forces is the fuction of following.
(a) Dead load of structure Calculated as- F= ahW
(b) Ground motion where F=horizontal forces owing to earthquake
(c) Period of vibration ah=seismic coefficients for respective regions
(d) Nature of soil W=DL+LL acting above the section
27. Some basic points regarding WSM and LSM
Working Stress Method
The Stresses in an element is obtained from the working loads and compared with
permissible stresses.
The method follows linear stress-strain behaviour of both the materials.
Modular ratio can be used to determine allowable stresses. For bridge construction in
case of WSM the Modular ratio is constant 10.
Material capabilities are under estimated to large extent. Factor of safety are used in
working stress method.
The member is considered as working stress.
Ultimate load carrying capacity cannot be predicted accurately.
The main drawback of this method is that it results in an uneconomical section.
All kind of major structure or important structure like bridge construction & tank
construction (rectangular tank & intz tank etc.) is still usually designed by only WSM.
Limit State Method
The stresses are obtained from design loads and compared with design strength.
In this method, it follows linear strain relationship but not linear stress relationship (one
of the major difference between the two methods of design).
The ultimate stresses of materials itself are used as allowable stresses.
The material capabilities are not under estimated as much as they are in working stress
method. Partial safety factors are used in limit state method.
28. T-BEAM BRIDGE
This is most commonly adopted type of bridge for span range of 10 to 25m.
It is so name because the main longitudinal girder are designed as T-beam
which is integral part of deck slab cast monolithically with the deck slab.
Simply supported T-beam spans of over 25m are rare as the dead load then
becomes too heavy. However there is a bridge have single span of 35m named
“ Advice bridge” in “Goa”.
In other words we can say T-beam bridge is the combination of [ deck slab with
longitudinal girders & cross girders ] superstructure & [piers , abutment &
foundations] substructure.
29. COMPONENT OF A T-BEAM BRIDGE
Deck slab
Cantilever portion
Longitudinal girders
Cross girders
Abutments & piers
Bearing
Foundations
30. Design of deck slab
It is designed by either “effective width method” or by “Pigeauds curve
method” as bending moment calculation.
After calculation of bending moment we provide reinforcement and
then do check for shear as accordance by WSM mtehod of RCC design.
Normal depth of deck slab is very from 350mm to 500mm.
EFFECTIVE WIDTH METHOD
It is applicable when the slab is designed by assuming its a one way slab
or supported only on two apposite edge or a very long slab supported
on all four edge.
Effective width is the width of wheel imprint on deck perpendicular to
the movement of vehicle that is actually bears the load of wheel tyre it
is calculated by following expressions.
FOR SIMPLY SUPPORTED CASE
beff.=k x(1-x/L) + bw
FOR CANTILEVER CASE
beff=1.2x + bw
31. Where beff= effective widht of dispersion
k = constant depend upon b/L (widht/length) ratio specified in IRC-6.
X=Distance of center of gravity of wheel from the nearest support in case of simply
supported and distance of center of gravity of wheel From the cantilever phase. in
case of
L= effective span of bridge in case of simply supported and clear span in case of
cantilever.
bw= w+2h (width of wheel + 2 thickness of wearing coat)
EFFECTIVE LENGTH OF DISPERSION
In the same manner as effective width of dispersion there is also a effective length of
dispersion measured along the direction of movement of vehicle.
calculated as- for both simply supported case as well as cantilever case
dispersion length= length of tyre contact + 2(overall thickness of deck including
wearing coat)
LEFF.= B + 2(D+2h) where Leff.=effective length of dispersion
d=overall thickness of bridge deck
h=thickness of wearing coat
32. Pigeauds method
short span(B) & long span(L) bending moment coeeficients are read
from curves developed by M. Pigeaud.
Used for only 2-way slab design or slabs supported along four edges
with restrained corners and subjected to symmetrically placed loads
distributed over some well defined area.
Curves developed for thin plates using the elastic flexural theory.
However their use has been extended to concrete slab too.
Poision’s ratio of 0.15 is considered.
The short span(B) & long span (L) bending moment is calculated by
following expressions.
short span B.M.=W(m1 +0.15m2) along the widht(B) of slab.
long span B.M.=W(0.15m1 +m2) along the length (L) of slab.
33.
34.
35.
36. Design of cantilever slab portion
It designed by effective width method only. The cantilever slab portion
slab portion usually carries the KERB , HANDRAILS , FOOTHPATH if
provided and a part of carriageway.
The critical section for bending moment is the vertical section at the
junction of the cantilever portion and the end of longitudinal girder.
The design bending moment for cantilever slab portion is calculated as
the sum of 0.2 times of dead load bending moment plus 0.3 times of
live load bending moment.
design moment= 0.2 dead load BM + 0.3 live load BM
37. Design of longitudinal girder
There are 3 method of design of longitudinal girder
(a) courbon’s method
(b) Hendry-jaegar method
(c) Morice and little version of huyon and massonnet method
In india the courbon’s method is standerized for design of longitudinal
girder.
normal size of longitudinal girder is (300×1200)mm
Courbon’s method
According to his theory no flexural of transverse deck is possible
because of presence of infinitely rigid diaphragms ( cross girder or
cross beam) and a concentrated load instead of one pushing down
only nearly girders , causes equal deflection of all girders.
The design bending moment for longitudinal girder is calculated with
the help of rection factor or distribution coefficient which is calculated
by following expressions given by courbon.
38.
39. Where W=ecentric concentrated load
n= no. of longitudinal girder
e=ecentricity of the wheel load from center line of the deck
x1=distance of girder under considerations from central axis of the beam
Σx2 = sum of distance of longitudinal girders from the centre line of deck
LIMITATIONS OF COURBON’S METHOD O THEORY
(a) span-width ratio should be between 2 to 4.
(b) Atleast five symmetrical cross girder connecting the longitudinal girders
(c) The minimum depth of cross girder should be atleast ¾ depth of longitudinal
girder.
40. Design of cross girder
Provided mainly to stiffen the girders and to reduce torssion in the
exterior girders.
Another function of the cross beam is to equalize the deflections of the
girders carrying heavy loading with those of the girders with less
loading.
This is particularly important when the design loading consist of
concentrated wheel loads such as IRC CLASS AA Loading to be placed
in most unfavourable positions.
The thickness of cross beams should not be less than the minimum
thickness of the webs of longitudinal girders.
The depth of the end cross girders should be such as to permit access
for inspection of bearings and to facilitate positionings of jacks for
lifting of superstructure for replacement of bearings.
normally we use same size as that of longitudinal girders.
Dead load bending moment is computed considering a trapezoidal
distribution of weight of deck slab and wearing coarse.
The live load bending moment is calculated as the bending moment
calculated simply for a beam.
42. PIERS
A support of concrete or masonry for superstructure of bridge.
The base of a pier may rest directly over firm round or it may be
supported on piles.
Center line of pier normally coincide with the center line of the
superstructure. The dimensions of the top of a pier depends on
distances between girder(longitudinal girder) and distance required to
provide for the expansion of girder , size of bearing etc.
IRC 40 gives minimum top width of pier and abutment.
Basic Types of Bridge Piers
43. Design loads for piers
a) dead load of superstructure
b) Dead load of pier
c) Live load on superstructure
d) Lateral forces perpendicular to centerline of superstructure (wind portion on
pier above water level , presure due to water , wave action of current)
e) Longitudinal forces parllel to the direction of the bridge (includes braking of
vehicles , tractive force of vehicle (high in case of train)).
f) Seismic force.
ABUTMENTS
An abutment is a structure that support one end of a bridge in other word
we can say that it is a structure located at the end & at the beginning of a
bridge.
Functions of abutment
a) Support the bridge deck at end.
b) Retain the embankment of approaching road.
c) Connected the approach road to the bridge deck.
44. Basic Types of Bridge Abutments –
Wall & Counterfort
Wall Abutment Counterfor
t
47. Forces acting on abutment
Dead load due to superstructure
Live load on superstructure
Self weight of abutment
Longitudinal forces (traction and boiling)
Earth presure due to soil embankment
Design of abutment
Hieght- Kept equal to hieght of pier
Abutment- provided with a better of 1 in 3 to 1 in 6 or it may be stepped down
Abutment width- top width according to space needed by the single bearing and bottom
width 0.4 to 0.5 times of height of abutment
Length- minimum equal to width of bridges
Abutment cap- thickness 450 to 600 mm.
Stability of abutment
It should be chack and safe against the following-
Oveturning
Sliding
Ecentricity of resultant with respect to center of the base
Maximum base presure or earth presure .
48. BEARING
Bearing are mechanical arrangement provided in the superstructure to transmit
the load to the sub- structure. Thus it is a via media between superstructure and
sub-structure which transmit the load from superstructure in such a manner
that bearing stresses induced in the subset are within permissible limits.
Purpose of bearings
To absorb movements of girder
To distribute load on a large area
To keep compressive stress within safe limits
To simplify the procedure in design
To take up the vertical movement due to sinking of the the support.
Type or category of bearing
Free bearing or expansion bearing
free to slide or move or roll and thus it allows longitudinal movement of girder.
Fixed bearing
it allows free angular movement and it does not permit any longitudinal
movement of the girder
49. Free bearing or expansion bearing are of following type-
RC rocker expansion bearing
Elastomeric bearing
Steel roller –cum rocker bearing
Sliding own rocker bearing
Sliding plate bearing
Fixed bearing are of following type-
Rocker bearing
Steel hinge
Steel rocker bearing
RC rocker fixed bearing
FORCES ON BEARING
(1)Reactive forces (2) longitudinal forces (3)uplift forces (4)transverse forces
MATERILAS FOR BEARING
(1)Cast steel (2)mild steel (3) lead (4)RCC (5)Rubber (6)Tar paper (7) Kraft
paper
50. BASIS FOR SELECTION OF BEARING
a) High vertical load taking capability.
b) Rotational capability.
c) Good seismic resistance
d) Overall cost (initial, maintenance) should be low.
e) Capability to resist external horizontal forces.
f) Aesthetic considerations.
51. Typical view of complete T-Beam bridge construction arrangement
REFERENCE-
“D.J. VICTOR”
THANK YOU
(for giving your valuable time)
