Chapter 4 Abutment Example

8/17/2019 Chapter 4 Abutment Example

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FUNDAMENTALS OF BRIDGE DESIGN Chapter

6

School of Civil Enineerin S!"#Str!ct!re$ % Bearin$

6.1 BEARINGSINTRODUCTION

Bearings are structural devices positioned between the bridge superstructure and the substructure.Their principal functions are as follows:

• To transmit loads from the superstructure to the substructure, and• To accommodate relative movements between the superstructure and the substructure.

The forces applied to a bridge bearing mainly include superstructure self-weight, traffic loads,wind loads, and earthquake loads. Movements in bearings include translations and rotations.

reep, shrinkage, and temperature effects are the most common causes of the translational

movements, which can occur in both transverse and longitudinal directions. Traffic loading,construction tolerances, and uneven settlement of the foundation are the common causes of the

rotations.

!sually a bearing is connected to the super-structure through the use of a steel sole plate and rests

on the sub-structure through a steel masonry plate. The sole plate distributes the concentrated

bearing reactions to the super-structure. The masonry plate distributes the reactions to thesubstructure. The connections between the sole plate and the super-structure, for steel girders, are

by bolting or welding. "or concrete girders, the sole plate is embedded into the concrete with

anchor studs. The masonry plate is typically connected to the substructure with anchor bolts.

Types of Bearings

Bearings may be classified as fi#ed bearings and e#pansion bearings. "i#ed bearings allowrotations but restrict translational movements. $#pansion bearings allow both rotational and

translational movements. There are numerous types of bearings available. The following are the

principal types of bearings currently in use.

Roller Bearings

%oller bearings are composed of one or more rollers between two parallel steel plates. &ingle roller bearings can facilitate both rotations and translations in the longitudinal direction, while a group of

rollers would only accommodate longitudinal translations. 'n the latter case, the rotations are

provided by combining rollers with a pin bearing.

%oller bearings have been used in both steel and concrete bridges. &ingle roller bearings arerelatively cheap to manufacture, but they only have a very limited vertical load capacity. Multiple

roller bearings, on the other hand, may be able to support very large loads, but they are much moree#pensive.

Lect!re note "& S!rafel T . (


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Sliding Bearings

) sliding bearing utili*es one plane metal plate sliding against another to accommodate

translations. The sliding bearing surface produces a frictional force that is applied to the

superstructure, the substructure, and the bearing itself. To reduce this friction force, +T"$ poly-tetrafluoro-ethylene is often used as a sliding lubricating material. +T"$ is sometimes referred to

as Teflon, named after a widely used brand of +T"$. 'n its common application, one steel plate

coated with +T"$ slides against another plate, which is usually of stainless steel.

Elastomeric Bearings

)n elastomeric bearing is made of elastomer either natural or synthetic rubber. 't accommodates both translational and rotational movements through the deformation of the elastomer. $lastomer is

fle#ible in shear but very stiff against volumetric change. !nder compressive load, the elastomer

e#pands laterally. To sustain large load without e#cessive deflection, reinforcement is used to

restrain lateral bulging of the elastomer. This leads to the development of several types of elastomeric bearing pads plain, fiberglass-reinforced, cotton duck-reinforced, and steel-

reinforced elastomeric pads.

&teel reinforced elastomeric bearings and steel plate/+T"$ +oly-tetrafluoro-ethylene. &liding

bearings are relatively cheap and require a minimal construction height. &teel reinforced

elastomeric bearings can take movements in all directions but only to a certain limit. They aretherefore suitable for small or medium si*ed bridges. The bearing has to be changed after some 01

- 21 years when the rubber is worn out.

DESIGN $%) Bridge 3esign Manual 411(

Contact Stresses!nless otherwise noted, the resistance factor for bearings, ϕ, shall be taken as (.1.

"riction for bearings: &teel roller bearings and steel plate bearings with +T"$ layer in-between

shall be designed with a friction factor of 2 5 of the actual vertical load.

)t the service i!it state, the contact load, +s, shall satisfy:

• "or cylindrical surfaces:

Lect!re note "& S!rafel T . 4

−

≤s

y

4

(

(s

$

"

3

3(

637+

4

4


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7.(

• "or spherical surfaces:

7.4

where: 3( 8 the diameter of the roller surface mm, and34 8 the diameter of the mating surface mm taken as:

• +ositive if the curvatures have the same sign, and

• 'nfinite if the mating surface is flat."y 8 specified minimum yield strength of the weakest steel at the contact surface M+a

$s 8 9oungs modulus for steel M+a6 8 6idth of the bearing mm

The service limit state loads are limited so that the contact causes calculated shear stresses nohigher than "y#$ or surface compression stresses no higher than 1.%& "y. The ma#imum

compressive stress is at the surface, and the ma#imum shear stress occurs ;ust below it.

Concrete S'pporting t(e Bearing

'n the absence of confinement reinforcement in the concrete supporting the bearing device, the

factored bearing resistance, +r , shall be taken as:

+r 8 ϕ+n for which: 7.0

+n 8 1.72 fc )( m 7.


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6here the supporting surface is sloped or stepped, )4 shall be taken as the area of the lower base

of the largest frustum of a right pyramid, cone, or tapered wedge contained wholly within the

support and having for its upper base the loaded area, and having side slopes of (.1 vertical to 4.1hori*ontal as shown in "igure 7-0 below.

6hen the factored applied load e#ceeds the factored resistance, as specified herein, provisions

shall be made to resist the bursting and spilling forces.

)oa* +ates an* Anc(or Bots

)oa* +ates

The bearing together with any additional plates shall be designed so that:

• The combined system is stiff enough to prevent distortions of the bearing that would impair its proper functioning.

• The bearing can be replaced within a ;acking height of


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Anc(orages an* Anc(or Bots

)ll girders shall be positively secured to support bearings by a connection that can resist thehori*ontal forces that shall be imposed on it. &eparation of bearing components shall not be

permitted. onnections shall resist the least favorable combination of loads at the &trength imit

&tate and shall be installed wherever deemed necessary to prevent separation.

The factored resistance of the anchor bolts shall be greater than the factored force effects due to&trength ' or '' load combinations and to all applicable e#treme event load combinations. The

tensile resistance of anchor bolts shall be determined. The shear resistance of anchor bolts and

dowels shall be determined.

+T"E +oly-tetrafluoro-ethylene

"or all applications, the thickness of the +T"$ shall be at least (.2 mm after compression.%ecessed +T"$-sheet shall be at least


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oefficient of "riction

6here friction is required to resist non-seismic loads, the design coefficient of friction under

dynamic loading shall be taken as not more than (1 percent of the values listed in Table 7-( for the

bearing stress and +T"$ type indicated.

The coefficients of friction in Table 7-4 are based on a 1.41 µm finish mating surface. oefficientsof friction for rougher surface finishes must be established by test results.

+ressure

M+a

oefficient of "riction

0.2 ? (< D41

Type +T"$ Temperature o

3impled ubricated 41

-42

1.1<

1.17

1.10

1.1


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The ma#imum shear deformation of the bearing, at the service limit state, ∆s, shall be taken as ∆o,modified to account for the substructure stiffness and construction procedures. 'f a low friction

sliding surface is installed, ∆s need not be taken to be larger than the deformation corresponding tofirst slip.

The bearing shall satisfy: hrt ≥ 4s 7.(46here:hrt total elastomer thickness mm

s 8 ma#imum shear deformation of the elastomer at the service limit state mm

The shear deformation shall be limited in order to avoid rollover at the edges and delaminating due

to fatigue.

S(ape "actor

The shape factor of a layer of an elastomeric bearing, & i, shall be taken as the plan area of the layer

divided by the area of perimeter free to bulge. "or rectangular bearings without holes, the shape

factor of a layer shall be taken as:

&i 8 6 7.2

4hri I 6

where: 8 length of a rectangular elastomeric bearing parallel to longitudinal bridge a#is mm

68 width of the bearing in the transverse direction mm

hri thickness of ith elastomeric layer in elastomeric bearing mm

Goles are strongly discouraged in steel-reinforced bearings. Gowever, if holes are used, their effect

should be accounted for when calculating the shape factor because they reduce the loaded area and

increase the area free to bulge. The suitable shape factor formula for rectangular bearings is (

6- Σ π d4

&i 8 JJJJJJJJ


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σs ≤ 4.1 F & ≤ (4.1 M+a 7.E

σ ≤ (.1 F & 7.(16here: σs 8 service average compressive stress due to the total load M+a

σ 8 service average compressive stress due to live load M+a F 8 shear modulus of elastomer M+a

& 8 shape factor of the thickest layer of the bearing

These provisions limit the shear stress and strain in the elastomer. The relationship between the

shear stress and the applied compressive load depends directly on the shape factor, with higher shape factors leading to higher capacities.

ompressive 3eflection of $lastomeric Bearings

3eflections of elastomeric bearings due to total load and to live load alone shall be consideredseparately. 'nstantaneous deflection shall be taken as:

δ 8 i hri 7.((

where: i 8 instantaneous compressive strain in ith elastomer layer of a laminated bearing

hri 8 thickness of ith elastomeric layer in a laminated bearing mm

Kalues for i shall be determined from "igure 7-< stress strain curve, test results or by analysis

when considering long-term deflections. The effects of creep of the elastomer shall be added to the

instantaneous deflection. reep effects should be determined from information relevant to the

elastomeric compound used, or from the above specifications.

imiting instantaneous deflections is important to ensure that deck ;oints and seals are not

damaged. "urthermore, bearings that are too fle#ible in compression could cause a small step inthe road surface at a deck ;oint when traffic passes from one girder to the other, giving rise to

impact loading. ) ma#imum relative deflection across a ;oint of 0 mm is suggested. Loints and

seals that are sensitive to relative deflections may require limits that are tighter than this.

"igure 7-


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The provisions of this section shall apply at the service limit state. %otations shall be taken as thema#imum sum of the effects of initial lack of parallelism and subsequent girder end rotation due to

imposed loads and movements.

Bearings shall be designed so that uplift does not occur under any combination of loads and

corresponding rotations.

%ectangular bearings shall be taken to satisfy uplift requirements if they satisfy:

4

ri

s

s

h

B

nF&1.(

θ


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++

=

6<

(-41&,&

C?.4B

7.(?

6here: F 8 shear modulus of the elastomer M+a 8length of a rectangular bearing parallel to longitudinal bridge a#is mm

6 8width of the bearing in the transverse direction mm

"or a rectangular bearing where is greater than 6, stability shall be investigated by interchanging

and 6 in $quations 7.(C and 7.(?.

"or rectangular bearings, the service average compressive stress due to the total load, σs, shallsatisfy:

• 'f the bridge deck is free to translate hori*ontally:

s @ F 7.(7 4) - B

• 'f the bridge deck is fi#ed against hori*ontal translation:

B)

Fs

−≤σ

Reinforce!ent of Bearings

The thickness of the steel reinforcement, hs, shall satisfy the following:

• )t the service limit state:

y

sma#r s

"h0h σ≥ 7.41

• )t the fatigue limit state:

TG

sma#r

s

"

h1.4h

∆σ

≥ 7.4(

6here: "TG 8 onstant amplitude fatigue threshold of (C2 M+a

hr ma# 8 thickness of thickest elastomeric layer in elastomeric bearing mm 8 service average compressive stress due to live load M+a

s 8 service average compressive stress due to total load M+a

"y yield strength of steel reinforcement M+a

'f holes e#ist in the reinforcement, the minimum thickness shall be increased by a factor equal to

twice the gross width divided by the net width.

Lect!re note "& S!rafel T . (1


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Design E5a!pe

"or the girder bridge that is designed in chapter 2superstructure design design an $lastomeric

bearing that can be placed between the abutment and e#terior girder.

Given

8 e#pandable span length 8 (C.Cm

Reaction for! gir*er *esign

% 3 8 &elf weight reaction 8 40(.< N=

8%eaction due to the diaphragm 8 0.1< N=

%$.7N

8 36 reaction O 8 41.42 N=

% 8 reaction without impact/girder

ane load 8 20.1< N= Truck load 8 4CC.C0N=

$18.697N

qs 8 bearing design rotation at service limit state 8 1.142 rad

∆T 8 ma#imum temperature change 8 42P

∆&G 8 girder shortening due to concrete shrinkage 8 (1 mmF 8 shear modulus of elastomer 8 1.E Q (.07 M+a

γ 8 load factor for uniform temperature, etc. 8 (.4

Lect!re note "& S!rafel T . ((


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!sing C1 durometer reinforced bearing:

F y 8 yield strength of steel reinforcement 8 021 M+a

&liding bearing used:

1. Te!perat're ,ove!ent

"or normal density concrete, the thermal coefficient is

%. Gir*er S(ortenings

$. Bearing T(ic:ness

hrt8 total elastomer thickness

hri8 thickness of ith elastomeric layer

n8 number of interior layers of elastomeric layer ∆s 8 bearing ma#imum longitudinal movement 8 γ . ∆T$M+ I ∆&G∆s 8 (.4 #


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1.CCF&81.CC(M+a


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. Bearing Sta-iity

Bearings shall be designed to prevent instability at the service limit state loadcombinations.

"or a rectangular bearing where is greater than 6, stability shall be investigated by

interchanging and 6 in $quations 7.(C and 7.(?.

6here

4)841.1(7C 8 D B 8 1.144< S.. heck using eq. 7.(7

SSSSSSSSVN

8. Bearing Stee Reinforce!ent

The bearing steel reinforcement must be designed to sustain the tensile stresses induced by

compression of the bearing. The thickness of steel reinforcement, hs, should satisfy:

At the service limit state:

6here hma# 8 thickness of thickest elastomeric layer in elastomeric bearing 8 hri.

Easto!eric Bearings Detais

"our interior lays with 41 mm thickness each layer

Two e#terior lays with (1 mm thickness each layer

"ive steel reinforcements with 1.E mm each

Total thickness of bearing is (1


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Bearing si*e:


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"rom the view of the relation between the bridge abutment and roadway or water flow that the

bridge over crosses, bridge abutments can be divided into two categories: open en* a-'t!ent an*

cose* en* a-'t!ent,

I. Open en* a-'t!ent

'n open end abutment there are slopes between the bridge abutment face and the edge of the

roadway or river canal that the bridge over crosses. Those slopes provide a wide open area for

the traffic flows or water flows under the bridge 't imposes much less impact on the

environment and the traffic flows under the bridge than a closed-end abutment. )lso, future

widening of the roadway or water flow canal under the bridge by ad;usting the slope ratios is

easier. Gowever, the e#istence of slopes usually requires longer bridge spans and some e#tra

earthwork. This may result in an increase in the bridge construction cost.

Vpen $nd, Monolithic Type )butment Vpen $nd, &hort &tem &eat Type )butment

II. Cose* En* A-'t!ent

The closed-end abutment is usually constructed close to the edge of the roadways or water

canals. Because of the vertical clearance requirements and the restrictions of construction

right of way, there are no slopes allowed to be constructed between the bridge abutment faceand the edge of roadways or water canals, and high abutment walls must be constructed. &ince

there is no room or only a little room between the abutment and the edge of traffic or water

flow, it is very difficult to do the future widening to the roadways and water flow under the

bridge. )lso, the high abutment walls and larger backfill volume often result in higher abutment construction costs and more settlement of road approaches than for the open-end

abutment.

Lect!re note "& S!rafel T . (C


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losed $nd, Monolithic Type )butment losed $nd, Gigh &tem seat Type )butment

"rom the view of the how the bridge abutment support the embankment we can classify the bridge

abutments into different categories.

I. "' >eig(t A-'t!ent

) full height abutment is constructed at the lower level roadway and should support the entire

embankment. This abutment is costly and is generally used in congested urban andmetropolitan area where structure depth is critical.

II. Se!i/st'- A-'t!ent

) semi-stub abutment is constructed somewhere between the top and bottom of an

embankment and its height is between height of full and stub abutment.

Lect!re note "& S!rafel T . (?


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III. St'- A-'t!ent

) stub abutment is built at the top of embankment slope and is considered as the best type of abutment for avoiding rough and settled approach pavements. ) stub abutment is economical

but gives a longer span length and a higher superstructure cost. Gowever, the overall

structure would be less costly than other alternate

I?. Integra A-'t!ent

'ntegral abutment is stub abutment on single row of fle#ible piles and constructed without

;oints. 'ntegral abutments allow the e#pansion and contraction through movement at theabutments.

ABUT,ENT T=+E SE)ECTION

The selection of an abutment type needs to consider all available information and bridge designrequirements. Those may include bridge geometry, roadway and riverbank requirements,

geotechnical and right-of-way restrictions, aesthetic requirements, economic considerations, etc.

Nnowledge of the advantages and disadvantages for the different types of abutments will greatly benefit the bridge designer in choosing the right type of abutment for the bridge structure from the

beginning stage of the bridge design.

DESIGN CONSIDERATION

Lect!re note "& S!rafel T . (7


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)butment design loads usually include vertical and hori*ontal loads from the bridgesuperstructure, vertical and lateral soil pressures, abutment gravity load, and the live-load

surcharge on the abutment backfill materials. )n abutment should be designed so as to withstand

damage from the $arth pressure, the gravity loads of the bridge superstructure and abutment, liveload on the superstructure or the approach fill, wind loads, and the transitional loads transferred

through the connections between the superstructure and the abutment. )ny possible combinationsof those forces, which produce the most severe condition of loading, should be investigated in

abutment design.

)butment 3esign oads &ervice oad 3esign

)butment 3esign oads ase

' '' ''' 'K K

3ead load of superstructure

3ead load of wall and footing

3ead load of earth on heel of wall including surcharge

3ead load of earth on toe of wall$arth pressure on rear of wall including surcharge

ive load on superstructureTemperature and shrinkage

)llowable pile capacity of allowable soil pressure in 5 or basic

W

W

W

WW

W

(11

W

W

W

WW

(11

W

W

WW

(21

W

W

W

WW

WW

(42

W

W

(21

onfiguration of abutment design load and load combinations.

Lect!re note "& S!rafel T . (E


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!nder seismic loading, the abutment may be designed at no support loss to the bridge

superstructure while the abutment may suffer some damages during a ma;or earthquake.

The current ))&GTV Bridge 3esign &pecifications recommend that either the service load design

or the load factor design method be used to perform an abutment design. Gowever, due to the

uncertainties in evaluating the soil response to static, cycling, dynamic, and seismic loading, the

service load design method is usually used for abutment stability checks and the load factor

method is used for the design of abutment components.

"or the abutment with spread footings under service load, the factor of safety to resist sliding

should be greater than (.2 the factor of safety to resist overturning should be greater than

4.1 the factor of safety against soil bearing failure should be greater than 0.1. "or the abutment

with pile support, the piles have to be designed to resist the forces that cause abutment sliding,

overturning, and bearing failure. The pile design may utili*e either the service load design method

or the load factor design method.

SEIS,IC DEISGN CONSIDERATIONS

'nvestigations of past earthquake damage to the bridges reveal that there are commonly two types

of abutment earthquake damage stability damage and component damage.

)butment stability damage during an earthquake is mainly caused by foundation failure due to

e#cessive ground deformation or the loss of bearing capacities of the foundation soil. Those

foundation failures result in the abutment suffering tilting, sliding, settling, and overturning. The

foundation soil failure usually occurs because of poor soil conditions, such as soft soil, and the

e#istence of a high water table. 'n order to avoid these kinds of soil failures during an earthquake,

borrowing backfill soil, pile foundations, a high degree of soil compaction, pervious materials, and

drainage systems may be considered in the design.

)butment component damage is generally caused by e#cessive soil pressure, which is mobili*ed by the large relative displacement between the abutment and its backfilled soil. Those e#cessive

pressures may cause severe damage to abutment components such as abutment back walls and

abutment wingwalls. Gowever, the abutment component damages do not usually cause the bridge

superstructure to lose support at the abutment and they are repairable. This may allow the bridge

designer to utili*e the deformation of abutment backfill soil under seismic forces to dissipate the

seismic energy to avoid the bridge losing support at columns under a ma;or earthquake strike.

"or seismic loads in the transverse direction, the same general principles still apply. The C(mm

displacement limit also applies in the transverse direction, if the abutment stiffness is e#pected to

be maintained. !sually, wingwalls are tied to the abutment to stiffen the bridge transversely. Thelateral resistance of the wingwall depends on the soil mass that may be mobili*ed by the wingwall.

"or a wingwall with the soil sloped away from the e#terior face, little lateral resistance can be

predicted. 'n order to increase the transverse resistance of the abutment, interior supplemental

shear walls may be attached to the abutment or the wingwall thickness may be increased, as shown

in "igure. 'n some situations larger deflection may be satisfactory if a reasonable load path can be

provided to ad;acent bents and no collapse potential is indicated



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Based on the above guidelines, abutment analysis can be carried out more realistically by a trial

and error method on abutment soil springs. The criterion for abutment seismic resistance design

may be set as follows.

,onoit(ic A-'t!ent or Diap(rag! A-'t!ent

&eismic resistance elements for monolithic abutment. 6ith "ooting

&eismic resistance elements for monolithic abutment. 6ithout "ooting

Lect!re note "& S!rafel T . 4(

6ith "ooting $X % soil IKdiaphragm

EQT V ww + V key V keys = 0.75(V piles) for pilefooting

V keys = µ(Dead Load reaction@

6ithout "ooting $X % soil IKdiaphragm

EQT V ww +


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Seat/Type A-'t!ent

&eismic resistance elements for seat-type abutment.

6here

$X8 longitudinal earthquake force from an elastic analysis$XT8 transverse earthquake force from an elastic analysis

% soil8 resistance of soil mobili*ed behind abutment

% diaphragm8φ times the nominal shear strength of the diaphragm% ww8φtimes the nominal shear strength of the wingwall% piles8φtimes the nominal shear strength of the piles% keys8φtimes the nominal shear strength of the keys in the direction of considerationφ8 strength factor for seismic loadingY8 coefficient factor between soil and concrete face at abutment bottom

't is noted that the purpose of applying a factor of 1.?2 to the design of shear keys is to reduce the possible damage to the abutment piles. "or all transverse cases, if the design transverse earthquake

force e#ceeds the sum of the capacities of the wingwalls and piles, the transverse stiffness for the

analysis should equal *ero $XT 8 1. Therefore, a released condition which usually results inlarger lateral forces at ad;acent bents should be studied.


&eat Type )butment $X % soil

EQT V key V keys = V ww + 0.75(V piles) for pilefooting

V keys = V ww + µ(Dead Loadreaction @


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%esponding to seismic load, bridges usually accommodate a large displacement. To providesupport at abutments for a bridge with large displacement, enough support width at the abutment

must be designed.

The minimum abutment support width, as shown in "igure below, may be equal to the bridge

displacement resulting from a seismic elastic analysis or be calculated as shown in $quation below,

whichever is larger:

= 8 012 I 4.2 I(1G(I 1.114 &4

6here

=8 support width mm8 length m of the bridge deck to the ad;acent e#pansion ;oint, or to the end of bridge deck for

single-span bridges equals the length of the bridge deck

&8 angle of skew at abutment in degreesG8 average height m of columns or piers supporting the bridge deck from the abutment to the

ad;acent e#pansion ;oint, or to the end of the bridge deck G8 1 for simple span bridges

&eat Type )butment Monolithic )butment)butment support width seismic.

ABUT,ENT


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antilever 6ingwall &imple &upport 6ingwall

ontinous &upport 6ingwall

ive oad &urcharges for 6ingwall 3esign

Gighway truck loading

%ail loading $-C1

%ail loading $-?1

%ail loading $-71

4 ft 1 in. C(1 mm equivalent soil

? ft C in. 44E1 mm equivalent soil

7 ft E in. 4C?1 mm equivalent soil

(1 ft 1 in. 0121 mm equivalent soil

3esign loading for cantilever wingwall.

A-'t!ent Sope +rotection an* Drainage



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The drainage system embedded in the abutment backfill soil is designed to reduce the possible

buildup of hydrostatic pressure, to control erosion of the roadway embankment, and to reduce the

possibility of soil liquefaction during an earthquake.

"low water scoring may severely damage bridge structures by washing out the bridge abutment

support soil. To reduce water scoring damage to the bridge abutment, pile support, rock slope

protection and concrete slope paving may be used. The stability of the rock and concrete slope

protection should be considered in the design. )n enlarged block is usually designed at the toe of

the protections

Typical abutment drainage system.

,ISCE))ANEOUS DESIGN CONSIDERATIONS

$TG'V+')= %V)3& )!TGV%'T9 B%'3F$ 3$&'F= M)=!) - 4114

ABUT,ENTS

)butments shall be investigated for:

• lateral earth pressures, including any live and dead load surcharge,• the self-weight of the abutment• temperature and shrinkage deformation effects, and• $arthquake loads, as specified in Chapter )( Loa* Re+!ire,ent$-

)butments shall be investigated for e#cessive displacements at the service limit state.

$arth pressures used in design of abutments should be selected consistent with the requirement thatthe abutment should not move more than 02 mm laterally.

&urveys of the performance of bridges indicate those hori*ontal abutment movements less than 02

mm can be tolerated by bridge superstructures without significant damage-

3esign of abutments and walls shall be investigated at the strength limit states for:

• Bearing resistance failure,• ateral sliding,



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• $#cessive loss of base contact,• Vverall instability,• +ull out failure of anchors or soil reinforcements, and• &tructural failure.

The conditions governing the design depends on:• Type and function of retaining structure,• $arth pressure e#erted on the wall by the retained backfill,• Feometry of the ground and the structure,• &trength of the ground,• Fround deformability .• Froundwater, and• &welling pressure in clay backfills.

'n the design of abutment the factore* resistance, % % , calculated for each applicable limit stateshall be the nominal resistance, % n, multiplied by an appropriate resistance factor, .ϕ

)butments, piers, and retaining structures and their foundations and other supporting elementsshall be proportioned for all applicable oa* co!-inations specified in G)+T$% 0 oad "actors

and ombinations.


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The vertical stems of cantilever walls shall be designed as cantilevers supported at the base. )ne#pansion ;oint shall always be applied between % wingwall rigidly attached to the abutment and

a free standing % retaining wall.

Design E5a!pe

) concrete T-girder bridge that is designed in hapter 2 &uperstructure 3esign is proposed to

overcrossing a river as shown in "igure below. Based on the roadway requirement and

geotechnical information, an open-end, seat-type abutment is selected. The abutment in transverse

direction is (1m wide and with 2P skew. "rom the bridge analysis, the loads on abutment and

bridge displacements are as listed below:

)oa* fro! t(e Bri*ge Anaysis

&uperstructure dead load, % 3 8 40(.


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'''. ) full $arth quick analysis isnZt done here, only we conceder the displacement due to earth

quick as per the code requirement.

'K. 1.4m wide of wing wall is used in the design.

1. A-'t!ent S'pport


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%. A-'t!ent Sta-iity C(ec:

"igure below shows the abutment force diagram,

6here:-qsc 8 soil lateral pressure by live-load surcharge

qe 8 soil lateral pressure

+3 8 superstructure dead load

+ 8 ive load" 8 longitudinal live load due to breaking force

hsc 8 height of live-load surcharge

γ 8 unit weight of soil6i 8 weight of abutment component and soil block

)ongit'*ina ive oa* Braking "orce-B%:- hapter 4 +age ?

B% 8 425 of the vehicular live load

)long one direction one design lane loaded

B% 8 1.42(


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"8(.104.2N= 8 04.2N="or &uperstructure load vertical, "v 8 (.1% 3 I (.1% 36 I (.1% I'M

+3 8 (.140(.< I (1.7


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e 8 eccentricity of resultant of forces and the center of footing

M8 total moment to point )

%eferring to the Table above and $qs. C.4.( and C.4.4 the ma#imum and minimum soil

pressures under footing corresponding to different load cases are calculated. !sing &ervice

load design ' or 'K note: - they will give the ma#imum vertical load

+ 8 (1.(4 I 2( I C?.4 I (12.2E I 04.70 I 24.?C I 4C4.


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!sing oad factor method

(.423 I (.236 I(.?2 I(.2$G I (.02$K I(.2$&6here:-

$G S.Gori*ontal earth pressure

$K S.Kertical earth pressure $& S..$arth &urcharge due to live load

"or section A/A

q( 8 (.2 # 1.0(E(.


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)s 8 1.11(2 A (111 A 4


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!sing φ(CGere, d 8 ?11 ] cover ] diameter/4 8 ?11 ] ?2 ](C/4 8 C(? mm

Bearing pressure under abutment footing

a. Design forces3

&ection at front face of abutment stem design for fle#ural reinforcement:

qa-a 8 1.


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=o shear reinforcement needed.

&ince the minimum soil bearing pressure under the footing is in compression, the tension atthe footing top is not the case. Gowever, the minimum temperature reinforcing, C24 mm4/m

needs to be provided. !sing 2 at 012mm at the footing top yields

)s 8 C2C mm4/m VN

&. A-'t!ent


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No shear reinforcing needed.Since the ingall is alloed to be bro!en o" in a ma#or earth$%a!e& the ad#acent bridgecol%mns ha'e to be designed to s%stain the seismic loading ith no ingall resistance. he

ab%tment section& footing& and ingall reinforcing details are shon in ig%res *.7a

and b.

Lect!re note "& S!rafel T . 0C


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(a) ,b%tment t-pical section design (eample). (b) /ingall reinforcing (eample).

Chapter 4 Abutment Example

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Transcript of Chapter 4 Abutment Example