CONTENTS .. 51.NoPage No. 1.Syllabus 2.Unit - 11 Analysis
andDesign of Concrete Bridges: 3.Unit - 229 SteelBridges:Steel
superstructure: ...!i 4.Unit - 355 Substructure andFoundations:
5.Unit - 480 Construction and Maintenance: 6.Unit - 5104 Case
Studies: 6 SYLLABUS BRIDGE ENGINEERING(BCQ 3.12)
AnalysisAndDesignofConcreteBridges:Loadingstandards:IRCandRailway
loadingsReinforcedconcretebriqge decks: slab,T-beamandslab,arch,bow
string girder typesPrestressed concrete
bridges:simplespans,continuous decks;cantilever construction;
anchorage of tendons ;grounding oftendons. Steel Bridges: Steel
superstructure: Plate girder, box girder truss and arch typesCable
stayedbridges andsuspensionbridges;principles of design,aerodynamic
stability and vibrations; simplified designs. Substructure
AndFoundations:Substructure design:piers andabutments of different
typesFoundations:Shallow foundations,deep foundations,piles,wells
andpneumatic caisonsRiver training works.
ConstructionAndMaintenance:Bearing;metallicandelastomerictypes;fixedand
movablebearingsJoints:expansionjoints;ContractionjOints;jointsealsInnovative
constructionmethods;incrementalpushlaunching;cantilever
construction;erectionof
precastelementsBridgemaintenancemanagement:inventory,inspectionand
rehabilitation. CaseStudies:Casestudiesof
recentlyconstructedmajorbridgesCriticalstudiesof failure of major
bridges. UNIT - 1 : ANALYSIS ANDDESIGNOF CONCRETE BRIDGES SECTION A
MULTIPLE CHOICE QUESTIONS
1.Whiledesigningroadbridgesandculvert,whichofthefollowingloadisnot
considered? a)Dead Load b)Live Load c)Machine Load d)Snow Load
2.From consideration of safety and effective utilization of
carriageway, it is desirable to provide footpath of atleast a)1.5m
b)2.0m c)2.5m d)3.0m 3.What is the weight oftracked vehicle
considered in IRC Class MLoading: a)500kN b)600kN c)700kN d)None of
the above 4.What is the weight of wheeled vehicle considered in IRC
Class MLoading: a)300kN b)400kN c)500kN d)600kN 5.What is the
weight of tracked vehicle considered in IRC Class 70R Loading:
a)500kN b)600kN c)700kN d)None ofthe above BCO-3.12 6.What is the
weight of wheeled vehicle considered in IRC Class AA L,oading:
a)500kI\J b)BOOkN c)1000 kN d)1200kN 7.What is the value of Impact
Factor for concrete bridge of 3m span? a)0.5 b)0.6 c)0.7 d)O.B
B.What is the value of Impact Factor for steel bridge of 3m Span?
a)0.525 b)0.545 c)0.565 d)None ofthe above 9.On whatfactorthe
actual Impact Factor will depend: a)load on the bridge b)span ofthe
bridge c)spring constant ofthe bridge d)none ofthese 10.No live
load is considered to be acting on the bridge, ifthe wind velocity
at the deck exceeds: a)100km/h b)130km/h c)150km/h d)200km/h Answer
Key: 1.cI 2.8 3.c4.bS.c6.c 7.88. b9. c1 10. bI 2BCO-3.12 SECTION B
TRUE FALSE TYPE QUESTIONS 1 .A member is referred as post tensioned
member,if the tendons are stressed and anchoredateachendof
themember after the concretehasbeencast andhas attained sufficient
strength. 2.A special type of concrete arch bridges has been
developed by Robert Maillart. 3.A fixed arch is statically
determinate structure.
4.Therigidconnectionsresultsinmorestablesupports,thanpossiblewith
independent piers of comparable dimensions. 5.The continuous girder
bridge suffers less vibration and deflection AnswerKey: 1.
T2.T3.F5. T 3BCO-3.12 SECTION C SHORT ANSWER TYPE QUESTIONS 01
:What are the various loads considered in designing the road
bridge?
Ans:Whiledesigningroadbridgesandculverts,thefollowingloads,shouldbe
considered, where applicable: (a)Dead load (b)Live load (c)Snow
load (d)Impact or dynamic effect due to vehicles (e)Impact due to
floating bodies or vessels (f)Wind load 02:What are the various
forces considered in designing the road bridge? Ans:While designing
road bridges, the following forces should be considered:
(a)Longitudinal forces caused by the tractive effort of vehicles or
by braking of vehicles. (b)Longitudinal forces due to frictional
resistance of expansion bearings. (c)Centrifugal forces due to
curvature. (d)Horizontal forces due to water currents. (e)Buoyancy
(f)Earth pressure, including live load surcharge. (g)Forces and
effects due to earthquake 03:What is the role of IRC in designing
the road bridges?
Ans:TheIndianRoadCongress(IRC)hasformulatedStandardSpecificationsand
Codes of Practice for roadbridges with a view to estab.lish a
common procedure for the designandconstructionof
roadbridgesinIndia.Thespecificationsare collectively known as the
Bridge Code.Prior to the formulation of the IRC Bridge Code, There
was no uniform code for the whole country. Currently, we would
follow the IRC Bridge Code. 04:What arethedifferent typesof
IRCStandardsLiveLoadconsideredduring the design of road bridge?
Ans:There are four types of Standard Loadings for which road
bridges are designed: a)IRCClassAALoading b)IRC Class 70 R Loading
c)IRCClassALoading d)IRC Class B Loading 4BCO-3.12 05:What are the
different types of gauges used on Indian Railways? Ans:There are
three gauges used onIndianRailways with the widthof track between
the inner faces of rails as indicated below: (a) (b) (c) Broad
Gauge (BG) Metre Gauge (MG) Narrow Gauge (NG) 1676 1000 762 mm mm
mm (5'6) (3'3-3/S) (2'6) 06:What are the various standards the r a
i ~ w a ybridges are to be built to conform to the Indian Railway
Standard laid down by the Ministry of Railways? Ans:Railway bridges
in India are to be built to conform to the Indian Railway Standards
(IRS) laid down by the Ministry of Railways, Government of India,
as below: (a)The loads to be considered in design are given in IRS
Bridge Rules. (b)Thedetailsof
designofsteelbridgeshouldconformtoIRSSteelBridge Code. (c)The
details of design of bridge members in plain, reinforced and
prestressed concrete should be in accordance with IRS Concrete
Bridge Code. (d)Masonry ad plain concrete arch bridges should be
detailed so as to conform to IRS Arch Bridge Code.
(e)ThesubstructureforbridgesshouldbeinaccordancewithIRSBridge
Substructure Code. 07:What is the role of Admixture in Concrete?
Ans:Admixturesareavailable forincreasing the workabilityof
concrete(plasticizers) facilitatingthereductionof
watercementratioandforretardationof settingof cementduringhot
weatherconcreting.Concretepropertiessuchasdurability, strength and
service life can be enhanced by use of suitable mineral and
chemical admixtures. os:What are the various component of RMC
Plant? Ans:A typical RMC plant has the following components:
(i)Central batching plant with a capacity of 30 to 200m3 of
concrete per hour; (ii) (iii) Transit mixer trucks to transport
concrete to construction sites with the help of rotating type
transit mixers of capacity about 6 m3 ;and Concrete pumps and
conveyors to deliver concrete at the work sites. 09: Ans: What do
you mean by Ready Mix Concrete?
Atmanybridgesites,speCiallyinurbanareas,preparationofconcreteat the
constructionsitebecomes difficult due to non-availability of
adequate space for storage and handling of the constituent
materials and for mixing operations. When 5BCO-3.12 the
construction activities in a city are of such magnitude as to
assure a sustained demandforlargevolumeof
concrete,itisdesirabletoestablishreadymixed concrete (RMC)plants in
the outskirts of the city and to transport the concrete in special
transit mixer trucks to the construction site at the right time.
Though the use of RMC is not yet widespread in many Indian cities,
this development is inevitable in the near future. 010:What are the
different types of Concrete Bridges? Ans:The usual types of
reinforced concrete bridges are: j1.Slab brtdges; 2.Girder and slab
(T-beam) bridges; 3.Hollow girder bridges; 4.Balanced cantilever
bridges; 5.Rigid frame bridges; 6.Arch bridges; 7.Bow string girder
bridges. 011 :What are the different components of T-beam bridge?
Ans:The T-beam superstructure consists ofthefollowing components:
(i)Deck slab (ii)Cantileverportion (iii)Footpaths; if provided,
kerbs and handrails (iv)Longitudinal girders, considered in design
to be ofT-section (v)Cross beams or diaphragms (vi)Wearing course.
012:What are the disadvantages of Continuous Girder Bridge?
Ans:(a)Unevensettlement of foundations may lead to disaster.Hence
this type of
structuresshouldnotbeusedinsituationswhereunyieldingfoundations
cannot be obtained at a reasonable cost. (b)The detailing and
placing of reinforcements need extra care. (c)The sequence of
placing concrete and the sequence of removing formwork have to be
carefully planned. (d)Being statically indeterminate, the design is
more complicated than simple beams. 013:What are the various
consideration taken into account in case of arch axis? Ans:The arch
axis is generally governed by three considerations: 6BCO-3.12
(a)spanandrisefromtheroadgradient andnavigationor trafficclearances
below, (b)the economical shape from point of view of saving of
materials, and (c)the beauty ofthe intrados. 0.14.What do you mean
by post-tensioning? Ans.A member is referred as post-tensioned
member, if the tendons are stressed and anchored at each end of the
member after the concrete has been cast and attained sufficient
strength to withstand the prestressing force. 015:What is the role
oftendons in pretensioning? Ans:The tendonprovides a pre
compression force to reduce crackingunder service load and also
serves as tension reinforcement under the ultimate load condition.
The integrity of the grout duct and the surrounding concrete
governs the corrosion protection of the high-strength, low
ductility steel tendon.Grouting also helps to avoid fatigue failure
in the steel at the anchorages. 016:What are the various conditions
which meet the prestressing force? Ans:The prestressing force must
meet two conditions: 1.Itmust
providesufficientcompressivestresstooffset thetensilestresses which
will be caused by the bending moments. 2.It must not induce either
tensile or compressive stresses which are in excess ofthose
permitted by the specifications. 7BCO-3.12 SECTION 0 LONG ANSWER
TYPE QUESTIONS Q. 1.What are the various loads, forces &
stresses to be considered indesigning road bridge & culverts?
Ans.Whiledesigningroadbridgesandculverts,thefollowingloads,forcesand
stresses should be considered, where applicable: (a)Dead load
(b)Live load (c)Snow load (d)Impact or dynamic effect due to
vehicles (e)Impact dueto floating bodies or vessels (f)Wind load
(g)Longitudinal forces caused by the tractive effort of vehicles or
by braking of vehicles. (h)Longitudinal forces due tofrictional
resistance of expansion bearings. (i)Centrifugal forces due to
curvature. (j)Horizontal forces due to water currents. (k)Buoyancy
(I)Earth pressure, including live load surcharge. (m)Temperature
effects (n)Deformation effects (0)Secondary effects (p)Erection
stresses (q)Forces and effects dueto earthquake (r)Grade effect
(for design of bearings for bridges built in grade or cross fall)
(s)Wave pressure. The basic philosophy governing the design of
bridges is that a structure should be designed to sustain with a
defined probability allactions likely to occur withinits
intendedlifespan.Inaddition,thestructureshouldmaintainstabilityduring
unprecedented actions andshould have adequate durability during
itslife span. Typical combinations of loads and forces to be
considered in design and allowable increases in permissible
stresses for certainare given in the Code. It
willbenecessarytoensurethatwhensteelmembersareused,themaximum
stressunderanycombinationdoesnotexceedtheyieldstrengthofthesteel.
Based on observations from recorded earthquakes, it isnot
considered probable that wind load and earthquake will occur
simultaneously. 8BCO-3.12 Q.2.Describe theIRCClass Mloadings
andindicate theconditions under whichit should be used. Ans.(a)IRC
Class AA Loading. This loading consists of either a tracked vehicle
of 700 kN or a wheeled vehicle of 400 kN with dimensions as shown
in Fig. 1.1. The tracked vehicle simulates a combat tank used by
the army. The ground contact length of the track is 3.6 m and the
nose to tail length of the vehicle is 7.2 m. The nose to tail
spacing between two successive vehicles shall not be
lessthan90m.Fortwo-lanebridgesandculverts,one trainof Class M
trackedor wheeled vehicles whichever creates severer conditions
shall be considered for every two-lane width. No other live load
shall be considered onany part of the above two-lane carriageway
whenthe Class Mtrainof vehicles is on the bridge. The Class
Mloading is to be adopted for bridges
locatedwithincertainspecifiedmunicipallocalitiesandalongspecified
highways. Normally, structures on National Highways are provided
for these loadings. Structures designed for Class Mloading should
also be checked for Class A loading, since under certain
conditions, severe stresses may be obtai ':led under Class A
loading.
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