retrofit abutments

8/11/2019 Retrofit Abutments

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Retrofit Measures

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Pur ose

To describe typical retrofit measures for:

Abutments Footings


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Abutment retrofit measures

Approach slabs

Anchor slabs

Diaphragm walls

ransverse s ear eys Transverse soil anchors

Soil and gravity anchors


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California settlement (approach) slab

Design as SS 10 min Spans soil to deck

Connection FD isFD

F D S a

DL

0.6 Friction Coeff

Sa=Spectrum Acc

DL=Dead Load


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Abutment retrofit measures New Zealand settlement slab

ng e o ers ong u na res s ance

Still have smooth approach


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Waffle slab retrofit

2h

es s ance=. s

Resistance 16 pile=40 kips ultimate


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Anchor slab retrofit

Vertical capacity is of no concern

Must be securel connected to su erstructure Use damping ratio of 10%

Longitudinal forces will reduce 20%


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Must act composite Utilize dowels to provide

shear transfer


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Abutment retrofit measures Concrete transverse shear keys


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Concrete transverse shear keys


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Transverse soil anchors

Lateral resistance methods: Lateral capacity of piles

Passive pressure on wingwalls

Friction on bottom of footing Anchor slabs (previously discussed)

When these are not sufficient, consider soil anchors


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Wingwall cross-tie


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Abutment retrofit measures Abutment soil shear keys

-Pp=.96h ksf

Design tips

-To be fully effective:

clear space=2h

-Design shear for full passive pressure-Use R=2 for flexure

-Abutment connection designed

for overstrength moment

h


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Wing overlay


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Wing overlay


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CIDH pile shear key

Designed for lateralcapacity only

More effective when

fixed at top


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Deadman anchor

Extend anchors to avoid backfill movement Embed tie rods in concrete trench for protection


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Deadman anchor


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Abutment retrofit measures Soil anchors

Prestress ensures anchor is solid


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Abutment retrofit measures Abutment friction anchor

se w granu ar so s w e se emen

15 degree slope compresses slab as longitudinalmovemen occurs

Steel piles resist uplift


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Footin retrofit measures Footing strengthening

or s a y

Check moment at top


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Footin retrofit measures Footing concrete overlay

se over ay o ncrease nega ve momen capac y

Use added depth to check positive moment


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Footin retrofit measures

Reinforcing splice detail


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Footin retrofit measures

Prestressing

Use to help positive moment


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Footin retrofit measures ste 1

Determine design forces

Limit to flexural capacity of pier

Use overstren th moment Material stronger than expected

Confinement of concrete

Strain hardening of steel

Increase axial load from EQ


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Check OT capacity

If exceeded-check stability with a rocking analysis This may eliminate retrofit requirements


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Design for shear

Difficult to retrofit Increase footing depth with overlay

Add prestressing bars

Add vertical bars through drilled holes (must passbottom layer with hooks (anchors) to be effective or


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Design for flexure

Top reinforcing lacking very often Add overlay with steel and dowels

should be within thickness of footing from column

Extra depth helps positive moment Place prestress as close to column as possible


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Design dowels to connect to existing concrete

Should transfer shear stress at interface Use shear friction approach-friction=1.0

,

bottom is required-(difficult to do this)


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Footin retrofit measures ste 6 Check column-to-footing joint shear

Overlay capacity

Yield line theory

Easier to ust make overla thickerExample 10.1

retrofit of

footing


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Pil t f ti ti


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Pile to footin connection

Steel pipe piles filled with conc and rebar

Good connection to new footing

Can be drilled in low head room

Very stiff for lateral loads

Good connection to new footing

Pil t f ti ti


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Pile to footin connection Prestress tie down

roo oa e own

Pile capacity limits

amoun o

prestress

ue o oo ng

rotation, limited useto short columns

(before fully

effective-rotation

S


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Summar

To describe typical retrofit measures for:

Abutments Footings

Ab t t t fit


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Approach slabs

Anchor slabs Diaphragm walls

ransverse s ear eys Transverse soil anchors

Soil and gravity anchors


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