design of cantilever retaing wall

8/11/2019 design of cantilever retaing wall

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Design of CantileveredDesign of CantileveredRetaining WallsRetaining Walls

CE A433CE A433 RC DesignRC Design

T. Bart Quimby, P.E., Ph.D.T. Bart Quimby, P.E., Ph.D.

Spring 2009Spring 2009

IntroductionIntroduction

A cantilever retaining wall is a system ofA cantilever retaining wall is a system ofcantilever slabs (i.e. beams) that retaincantilever slabs (i.e. beams) that retainsoil.soil.

The key is to draw the appropriate FBDsThe key is to draw the appropriate FBDsso that you can determine the internalso that you can determine the internalforces.forces.

Cantilever Retaining WallCantilever Retaining Wall

Shear Key

Toe

Stem

Heel

Forces ACTING ON the WallForces ACTING ON the Wall

Wall

Footing

Shear Key

Soil on Toe

Soilon

HeelActiveLateral

SoilPressure

ReactionsReactions

PassiveLateral Soil

Pressure

VerticalReaction

Friction

ACTUAL FRICTIONis not the same as

FRICTION CAPACITY!

Computing Soil Bearing StressComputing Soil Bearing Stress

Resolve applied forcesResolve applied forcesinto a concentricinto a concentricvertical force andvertical force and

moment on the contactmoment on the contactarea.area.

IIxx = bL= bL33/12/12

A =A = bLbL

c = L/2c = L/2

maxmax = P/A + Mc/I= P/A + Mc/Ixx minmin = P/A= P/A Mc/IMc/Ixx

P

M


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SlidingSliding

DrivingForce

ResistingCapacity

Vslide = Driving Force= Demand

Vresist = sum(ResistingForces) = Capacity

FS =Vresist /Vslide

Design for

FS > 1.5

Friction CAPACITY = NNot Actual Friction Reaction

OverturningOverturning

DrivingForce

Point ofRotation

ResistingForces

MOT = Driving Force*arm= Demand

MROT = sum(ResistingMoments) = Capacity

FS = MROT / MOT

Design for

FS > 2.0

Draw FBDsDraw FBDs

Stem

ToeHeel

Stem DiagramsStem DiagramsFBD

Shear Moment

Capacity

Capacity

Makestem

thickenough

for shear

Select Steel to provide flexural capacity

AddT&S

Steel

ToeToe

Shear

Moment

Design Shear

Design Moment

Vu can becalculated a

distance d from

face of wall sincethere is acompressive

reaction with thewall.

Mu is computed atthe face of the

wall.

Flexural Steelextends a

development

length into theheel and shoulddevelop withinthe length of

the toe.

Add T&S Steel

HeelHeel

Shear

Moment

Design Shear

Design Moment

Vu must becalculated at the

face of wall since

there is a tensilereaction with thewall.

Mu is computed atthe face of the

wall.

Flexural Steel

extends adevelopment

length into thetoe and shoulddevelop withinthe length of

the heel.

Add T&S Steel


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The Design ProcessThe Design Process

Select the overall dimensions (height, embedment, footingSelect the overall dimensions (height, embedment, footinglength and position, and estimated footing & walllength and position, and estimated footing & wall

thicknesses) based on stability (sliding and overturning) andthicknesses) based on stability (sliding and overturning) andsoil strength (max/min bearing pressures) using service levelsoil strength (max/min bearing pressures) using service levelloads.loads.

Check slab (wall and footing) thicknesses using shear criteriaCheck slab (wall and footing) thicknesses using shear criteriaand factored loads. Adjust thicknesses as necessary,and factored loads. Adjust thicknesses as necessary,rechecking stability and soil strength of the values change.rechecking stability and soil strength of the values change.

Select the flexural steel for the three cantilever slabSelect the flexural steel for the three cantilever slabelements using factored loads.elements using factored loads.

Select the temperature and shrinkage steel for wall andSelect the temperature and shrinkage steel for wall andfooting.footing.

Draw the resulting wall cross section (to scale!)Draw the resulting wall cross section (to scale!)

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design of cantilever retaing wall