steel-dos-bridge lec 1 & 2

8/18/2019 Steel-DOS-Bridge Lec 1 & 2

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Civil Engineering Department – University of Engineering and Technology Lahore

Design of

Structures

STEEL BRIDGES

Bridges are the structures that allow movement ofhighway and railway traffic over natural or artificial

gaps in the topology of the area such as canals,

rivers, gap between hills and difference of level in

crossing roads etc

!election of type of bridge mainly depends

on"

• Local conditions,

• #vailability and cost of materials,

• $olume of traffic,

• !ite re%uirements,

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Design of

Structures

!election of type of bridge mainly depends

on" &cont'(• )eographical conditions,

• #esthetics

• E*pected economic return

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The design of bridges is further influenced by"

• The re%uired clearances,

• Erection possibilities,

• -oundation choices and

• .ydraulic characteristics of the stream, if one isinvolved

For example, a longer span may becomeeconomical in case the piers are veryexpensive to construct.


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Design of

Structures

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There are many structural differences betweena building and a bridge, some of these are"

For example, AASHTO Specification may be employed for

bridges in place of AISC Specification for steel buildings.

. !ridges are designed for "ea#y and concentrated mo#ing loads$"ereas buildings are usually designed for static distributedloads.

%. T"e impact of mo#ing loads is &uite considerable as compared

$it" residential and official buildings.'. Fatigue may become a problem and "ence may reduce t"e

strengt" due to large number of loading cycles.

(. )reater part of t"e structure is exposed to atmosp"ere.

*. T"e controlling design specifications for bridges are pro#ided by

organi+ations different from t"ose dealing $it" t"e buildingdesign.


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Design of

Structures

!teel bridges are classified depending on

their use into the following categories"

. Foot or pedestrian bridge used to carry pedestriantraffic, bicycles or small "and dri#en carts.

%. Hig"$ay bridges.'. ail$ay bridges.

(. Combined "ig"$ay and rail$ay bridges.

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Design of

Structures

Deck of Bridge

• A dec- is t"e actual carriage$ay of t"e bridge.• It consists of concrete or ort"otropic slab and $earing surface.

• Stringers and floor beams are also present for larger dec-s inaddition to t"e slab Figure /.

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Figure 1. Typical Steel Deck Supporting Elements.


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Design of

Structures

• 0epending upon t"e position of t"e longitudinalsupporting elements $it" respect to t"e dec-, t"ebridges may be dec- type or t"roug" type.

• A Deck Bridge is a bridge built at or near t"e tople#el of t"e main supporting members of t"esuperstructure, $"ic" "ang belo$ t"e dec- and arenot #isible from t"e bridge.

• In case of Through Bridge, t"e carriage$ay is

supported at t"e bottom of t"e main supportingmembers t"at are #isible $"ile tra#eling on t"ebridge.

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Deck or Through Bridge


7/50Civil Engineering Department – University of Engineering and Technology Lahore

Design of

Structures

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Truss Through Bridges are t"e bridges $"ere t"e dec- issupported on t"e lo$er c"ord of t"e truss.

T"e upper c"ord of t"e t$o longitudinal side trusses is braced.

T"e traffic mo#es t"roug" t"e t$o trusses and t"e top trans#ersebracing s"o$n in Figure %/.

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Figure 2. Typical Truss Through ri!ge.

Types of Steel Bridges



Design of

Structures

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!TEEL B+D)E! Types of Steel Bridges (cont…)



Design of

Structures

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A Fixed Bridge permanently remains in one position.

One or more parts of a Movable Bridge are made mo#able to allo$t"e #essels to pass t"roug" t"e stream underneat" in casesufficient clearance is not a#ailable.

T"e bridges are made mo#able in t"e "ori+ontal and t"e #ertical

planes.

Figure 3. $ine Diagram o% a &ertically

'o(a)le ri!ge.

Types of Steel Bridges (cont…)



Design of

Structures

•T"e main supporting elements of a steel bridge may berolled beams, plate girders, trusses and beams with

suspension cables.

o olled beams in non1composite bridges may be used for

spans up to 28 m.

o Composite rolled beams may be used for spans from 15 to38 m.

o 2late girders may be used for spans from 25 to 45 m.

o !ox girders are economical for spans from 45 to 75 m.

o Simply supported trusses are used for spans from 45 to 180

m.

o Continuous trusses are preferred for spans ranging from 75

to 240 m.

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Design of

Structures

• Slab Bridge is t"e one consisting of a simple one1$ayreinforced concrete slab $it"out any beams or trusses.

T"ese are used to co#er s"ort openings in t"e road

topology.

• Bea and Slab Bridges consist of reinforced concrete

slab supported o#er longitudinal steel beams Figure (/.

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Figure 4. +ast,in,-lace or -recast

+oncrete Sla) Supporte! )y Steel

eams.



Design of

Structures

12


If t"e steel beams in t"e abo#e type are continuouslyconnected to t"e slab by pro#iding s"ear studs or t"e

top flange of t"e beam is cast $it"in t"e concrete,

Composite Beam Bridge is obtained Figure */.

T"is type may be economical up to a span of 38 m.

Figure 5. +omposite Steel

eam ri!ges.



Design of

Structures

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/late )irder Bridges are used for spans of 25 to 45 m.

T"e dec- in t"ese bridges is supported on t$o

longitudinal plate girders present on t"e sides of t"e

road$ay.

If t"e plate girders are pro#ided belo$ t"e dec-, t"e

bridge is called plate girder deck bridge Figure 3/.

In case of plate girder through bridge, t"e traffic mo#es

on t"e dec- supported at t"e lo$er flange or at a certaindept" of t"e main member Figure 4/.




Design of

Structures

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Figure 6. Typical -late /ir!er

Deck ri!ge.

Figure 7. -late /ir!er

Through ri!ge.




Design of

Structures

In case of !rthotropic Deck Bridges, an ort"otropicdec- consisting of longitudinal folded steel plate resting

on cross girders, pro#ided at a spacing of 3 to 5 m.

T"e ca#ities of t"e plate are filled $it" tar and gra#el

and topped by $earing surface Figure 5/.

Figure ". n 0rthotropic Deck ith Steel Fol!e! -late.

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Design of

Structures

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Box "irder Bridge is used for cur#ed and longer spanbridges Figure 6/.T"ese bridges decrease t"e total dept" re&uirement andcan resist torsion to a large extent.

#ybrid "irder Bridges are t"ose plate girder or boxgirder bridges $"ere "ig" strengt" steel is used forflanges and ordinary steel is employed for t"e $eb of t"esupporting elements.

For spans in excess of 37 m, Suspension or $ableStayed Bridges may become economical.

8ine diagrams of t$o types of t"ese bridges are s"o$n in

Figure 7.



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Design of

Structures

Figure #. +ast,in,-lace

+oncrete Sla) o(er +lose!

Steel or -recast +oncrete

oes.

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Figure 1*. Suspension an! +a)le Staye! ri!ges.



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Design of

Structures

%re&stressed Steel Bridges are t"ose plate girderbridges in $"ic" t"e "ig" bending moment sections are

pre1stressed by "ig" strengt" steel tendons in a

direction opposite to t"e applied loading.

Figure 11. Eample o% a -re,stresse! +ontinuous ri!ge /ir!er.

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Design of

Structures

#dvantages of steel beam bridges

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Steel is a "ig" &uality, "omogeneous and isotropicmaterial t"at is perfectly elastic up to its yield point.

It "as e&ual and "ig" strengt"s in tension andcompression.

T"e material remains un1crac-ed and ex"ibitsappreciable ductility.

8esser construction time, compared $it" reinforcedand pre1stressed concrete bridges, reduces t"e o#erall

cost.T"e basic s-eleton of steel bridges may #ery easily beerected o#er #arious gaps in natural surface.

D i f


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Design of

Structures

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T"e design, erection and fabrication procedures forsteel bridges are #ery $ell establis"ed.

0ue to lesser self1$eig"t of t"ese bridges, t"e

foundation cost is also reduced.

For t"eir lesser dept"s, t"e steel bridges are preferred$"ere underneat" clearance is important.

epair, re"abilitation and up gradation of steel bridgesare usually easier t"an concrete bridges.

#dvantages of steel beam bridges &cont'(

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D i f


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Design of

Structures

)eneral Terms

• Stringers: These are longitudinal bridge deckbeams spanning between the transverse foorbeams and placed parallel to the roadway.

• Floor Beams: Floor beams are the main

girders o the bridge deck spanning betweentrusses or plate girders and runningperpendicular to the roadway.

• Core width is dened as the width o the

monolithic deck without the overhangs.• Footprint is the specied wheel contact areaover the roadway.

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D i f


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Design of

Structures

• Force Efect is dened as a deormation,stress or stress resultant caused by theapplied loads, imposed deormations.

• Lever Rule means the statical summation

o moments about any point to calculatethe reaction at some other point.

• Sew !ngle is dened as the anglebetween the centerline o a bridge support

and a line normal to the roadway centerline.• Two closely spaced and interconnected

axles o equal weight are together called a"andem.

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)eneral Terms &cont'(

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D i f


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Design of

Structures

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$oncrete Slab #aunch' A layer of concrete is usuallypro9ected belo$ t"e slab surface to surround top flangeof t"e steel beam, called concrete "aunc".

T"is "aunc" pro#ides lateral support to t"e top flange of

t"e steel beam and t"us pre#ents lateral buc-ling of t"ebeam.


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Design of


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Design of

Structures

Figure 13. +ross Frame.

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Diaphrag' T"is is a single steel member or a frameused to connect t"e longitudinal steel beams of a

bridge, pro#ided at t"e re&uired inter#al. 2art of a

typical cross frame is s"o$n in Figure '.


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Design of


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Design of

Structures

STEEL BRIDGES

Lecture 0 1

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Design of


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Design of

Structures

• T"e design lane "as a $idt" e&ual to t"e lesser of '377 mm or

$idt" of t"e traffic lane.• oad$ay $idt"s from 3777 to 4%77 mm s"all "a#e t$o design

lanes, eac" e&ual to one1"alf t"e road$ay $idt".

• T"e number of design lanes is ta-en as t"e integer part of t"eresult $"en t"e clear road$ay $idt" in mm bet$een curbs is

di#ided by '377.• If t"e design lanes are more t"an one, reduction factor of Table

6. is applied on t"e li#e load force effect called Multiple%resence Factor denoted by m.

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Design Lane

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#umber o$ Loaded

Lanes

%ultiple &resence

Factor .!"

! .""

# ".$%

".'%

Design of


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Design of

Structures

• H%7 means a "ig"$ay truc- $it" t$o axles and$eig"ing %7 tons.

• HS%7 means a "ig"$ay truc- similar to H%7 truc- but

"a#ing a semi1trailer $it" one additional axle.

• H* and HS* are defined in a similar $ay.

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Design $ehicular Live Load

!TEEL B+D)E!

8 kips 32 kips 8 kips 32 kips 32 kipsH20

6 kips 24 kips 6 kips 24 kips 24 kipsH15

HS20

HS15

Design of


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Design of

Structures

• T"e ne$ specification uses H86' "ig"$ay loading of66'/.

• In case of H86' loading, t"e #e"icular li#e load on t"e

bridge road$ay consists of a combination of design truc-

or design tandem/ and t"e design lane load.

• T"e design lane load s"all occupy a $idt" of '777 mm

trans#ersely $it"in a design lane

• All design lanes must be loaded simultaneously by t"e

truc- or tandem and t"e lane loads.

• T"e force effects from truc- or tandem load s"all besub9ected to dynamic load allo$ance of '':, but force

effects from t"e design lane load s"all not be sub9ected to

a dynamic load allo$ance.

2"


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Design of


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Design of

Structures

2#

View of HL-93 Design Truck Showing Axle Loads


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.L234 Loading &Design Truc5(

Design of


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Design of

Structures

• T"e design truc- or tandem s"all be placed

trans#ersely at '77 mm from t"e face of curb or

railing for t"e design of bridge o#er"ang and 377 mm

from edge of t"e design lane for t"e design of allot"er components.

• T"e design tandem s"all consist of a pair of 7 -;

axles at a longitudinal spacing of %77 mm $it" t"e

trans#erse center1to1center spacing of t"e $"eelsbeing 577 mm.

• T"e design lane load s"all be 6.' -;


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Design of

Structures

• A pedestrian load of '377 ;


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Design of

Structures

/a5istan Code 6f /ractice Loading -or

.ighway Bridges &7389(

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T"e "ig"$ay loading according to t"e 2a-istan Code of

2ractice for Hig"$ay !ridges consists of Class A, Class

! and Class AA loadings.

Design of


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Design of

Structures

$E $0DS D DST+ES F0 +$SS T8+9S

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!TEEL B+D)E! Class # : B Truc5s

Design of


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Design of

Structures

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!TEEL B+D)E! Class ## Tan5 Loading

Design of


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g

Structures

Ta)le . /roun! +ontact Dimensions.

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!TEEL B+D)E! Class # : B Truc5s

Design of


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g

Structures

Ta)le . Design Trans(erse Spacing eteen Trucks :;


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g

Structures

=>3 2>3 = *.43 = *.43 =

F0T $E E $E T$E $ES

= ? 25* k

5.62 m 4.14 m4."5 m

Fig. le $oa!s For 'erce!es en@ Truck.

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!TEEL B+D)E! ;ercedes Ben< Truc5

Design of


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g

Structures

Distribution of live load

• The truck loads on the bridge deck aremoving at di(erent locations along thewidth and length o the slab.

• )hen these loads occupy certain critical

positions, maximum orces occur in themembers.

• For approximate design o the deck, usuallyone*dimensional analysis is carried out

considering only the girder.• +n such cases, it becomes very important tond the e(ect o loads along the lateraldirection o the member.

3"

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Design of

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g

Structures

• stimating contribution o the transversely

placed loads -with respect to direction o tracmovement/ over the centerline o a particularmember, spanning along the length o thebridge, is called lateral distribution of loads.

• Thus, by the lateral distribution, equivalent loadsare obtained at the members.

• These equivalent loads are then placed along thelength o the member according to the criteria o

maximum orces in case o moving loads.• 0aximum orce e(ects are then obtained rom

this longitudinal distribution of the loads.

3#

Distribution of live load &cont'( !TEEL B+D)E!

Design of


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Structures

• 1owever, or beams or slab strips placedtransverse to the trac direction,longitudinal distribution o loads is to beperormed rst to get the equivalent loads.

• These equivalent loads are then placedtransversely at suitable locations to getextreme orces.

• This method o perorming manual *2analysis is called Approximate Method of

Analysis.

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Distribution of live load &cont'(

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Design of


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Structures

Conditions -or #ppro*imate ;ethod

• Spacing of beams, , s"ould be bet$een. and (.6 m.• T"ic-ness of dec- slab, t s, s"ould be bet$een 7 and

'77 mm.

• 8engt" of beam s"ould be bet$een 3.7 and 4'.7 m.

• ;umber of longitudinal beams in t"e cross1section, ;b,

s"ould be greater t"an or e&ual to (.

• T"e dec- cross1section s"ould be one of t"e standardtypes gi#en in t"e AASHTO Specification.

• T"e $idt" of dec- s"ould be constant.

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Design of


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Structures

• !eams s"ould be parallel and s"ould "a#eapproximately t"e same stiffness.

• T"e road$ay part of t"e o#er"ang, de, does not

exceed 67 mm.

• T"e gi#en expressions are only applicable to concrete

dec- on steel or concrete beams.

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Conditions -or #ppro*imate ;ethod cont=../

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Design of


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Structures

;otation >sed

S ? spacing o% )eams or e)s :mm<

L ? span o% )eam :mm<

N b ? num)er o% )eamsA stringers or gir!ers

t s ? !epth o% concrete sla) :mm<n ? mo!ular ratio )eteen )eam an! !eck

materials

I ? moment o% inertia o% )eam :mm4<

e g ? !istance )eteen the centers o%

the )asic

)eam an! !eck :mm


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Structures

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;otation >sed cont=../

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Design of

St t!TEE B+D)E!


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Structures

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;otation >sed cont=../

Design of

St t!TEEL B+D)E!


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Structures

Lateral Distribution -actors -or

nterior Beams

6ne design lane loaded

For Momen B

1.*

3

3.*4.*

43***6.*

+= s

g

t L K

LS S g

For Shear!

+=76**

36.* S

g

hen 4 1*# ≤ K g ≤ 3 1*12

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Design of

St t!TEEL B+D)E!


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Structures

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For Momen B

For Shear!

hen 4 1*# ≤ K g ≤ 3 1*12

1.*

3

2.*6.*

2#***75.*

+= s

g

t L

K

LS S g

*.2

1*7**36**2.*

−

+= S S

g


nterior Beams

Two or more design lanes loaded

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Design of

St t!TEEL B+D)E!


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Structures

• The distance, d e, shall be taken as

positive i the exterior web is within the

roadway and negative i it is outsidethe roadway.

• The expressions given below are

applicable or concrete deck on steel orconcrete beams.

Limitations: − #"" ≤ d e ≤ 3"


E*terior Beams

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4"

Design of

Structures!TEEL B+D)E!


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Structures

For Moment: 4se lever rule

For Shear: 4se lever rule


E*terior Beams6ne design lane loaded

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Two or more design lanes loaded

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Design of

Structures


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Structures

• + the transverse oor beams aredirectly supporting the deck slab, the

distribution actors are given in 5561T76pecication.

• 1owever, i the oor beams are takingload only rom longitudinally placed

stringers then lever rule may be used toget the distribution actors.

Distribution -actors -or Transverse

-loor Beams

!TEEL B+D)E!

steel-dos-bridge lec 1 & 2

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