Deck Overhang Presentation - Indiana Deck Overhang...Bridge Deck Overhang Design 2/7/2018 1 Bridge...

Bridge Deck Overhang Design 2/7/2018

1

Bridge Deck Overhang Design

Robert J. Frosch, PhD, PE, FACI

Professor of Civil EngineeringSenior Associate Dean of Facilities & Operations

Overhang Design

• Case 1

• Case 2

• Case 3

Faxle

Fv

Rw


2

0

5

10

15

20

25

30

2 4 6 8 10

Mom

ent

(ftꞏ

kip

/ft)

Overhang Length (ft)

Overhang Design for TL-4 Barrier

Case 1

Case 2

Case 3

Yield Line Analysis

+‐ ‐

Mc

Mw

· ∆

nominalrailingresistance


3

Barrier Design Forces

Design Forces and Designations Railing Test Levels

TL-1 TL-2 TL-3 TL-4 TL-5 TL-6

Ft Transverse (kips) 13.5 27.0 54.0 54.0 124.0 175.0

FL Longitudinal (kips) 4.5 9.0 18.0 18.0 41.0 58.0

Fv Vertical (kips) Down 4.5 4.5 4.5 18.0 80.0 80.0

Lt and LL (ft) 4.0 4.0 4.0 3.5 8.0 8.0

Lv (ft) 18.0 18.0 18.0 18.0 40.0 40.0

He (min) (in.) 18.0 20.0 24.0 32.0 42.0 56.0

Minimum H Height of Rail (in.) 27.0 27.0 27.0 32.0 42.0 90.0

Barrier Resistance

Rw = 150 kips >> Ft = 54 kips

• Overhang must resist larger moments and axial forces

• Barrier overdesign • more reinforcement

required in overhangs

INDOT Type FC TL-4 Barrier

33”

8”

#5, typ.

9”


4

Reducing Collision Forces

AASHTO procedure requires more reinforcement (~3 x Ft) Design for barrier capacity

Past practice required less reinforcement Lower design forces

INDOT and other states reduce collision force (1.25 x Ft) Design for transverse force

What is the appropriate design procedure?

Research Objective

Investigate appropriate design procedure

Determine failure mechanism in overhang specimens

Improve design assumptions


5

Schematic Design

15ft Specimen Design

A

A

#3, typ.

5”

16”

9”

4”

4.5”

Section A-ASpecimen #1 Specimen #2


6

Dial Gage

Experimental Setup

Strain Gages

Horizontal Pot.

Vertical Pot.

Jack w/ Load Cell

Dial Gage

Specimen #1 Cracking

Barrier Cracking Pattern


7

Specimen #2 Cracking

Barrier Cracking Pattern

Vertical Displacement

Specimen #1 Specimen #2

1.5 3.5 4.5 5.5 6.5 7.5 8.5 9.5 10.5 11.5 13.50

0.1

0.2

0.3

0.4

0.5

Potentiometer Location (ft)

Dis

plac

emen

t (in

.)

26.8k

25.1k

24.2k

22.4k

20.1k

1.5 3.5 4.5 5.5 6.5 7.5 8.5 9.5 10.5 11.5 13.50

0.1

0.2

0.3

0.4

0.5


Dis

plac

emen

t (in

.) 21.5k

20.1k

18.2k

17.7k


8

3’ Strip Specimens

• 5 full scale INDOT Type FC specimens

• 2 half scale specimens3’1’ TO BARRIER FACE

Full-Scale Specimen Design

33”

8”

#5

11”

Test Variables:

• Top Transverse Bar Size• #5 and #6

• End Condition• Straight and Hook

• Bar Coating• Epoxy coat and black

Varies

#4

Flat Face


9

Half-Scale Specimen Design

A

A

#3 hooked (Strip Sp. #6)

5”

16”

4”

4.5”

Section A-A

Specimen #1 and #2

#3 straight (Strip Sp. #7)

Slab Cast


10

Experimental Setup

Vertical Pot.

Jack w/ Load Cell Horizontal Pot.

Strain Gages

Full Scale Half Scale

#5 Epoxy @ 3.5” Straight14 kips

Full-Scale Cracking Behavior

#6 Epoxy @ 4.75” Straight14 kips


11

#5 Epoxy @ 3.5” Hooked15 kips


#5 Black @ 3.5” Straight15 kips

#6 Black @ 4.75” Straight14 kips


Typical Specimen Failure Plane


12

#3 @4.5” Hooked8 kips

Half-Scale Cracking Behavior

#3 @ 4.5” Straight6 kips

27ft Specimens

• Form Barrier Mechanism

Objectives

• Refine Distribution Length


13

27ft Specimen Design

A

A

hooked #3, typ.

5”

16”

9”

4”

4.5”

Section A-ASpecimen #1 Specimen #2

Experimental Setup

Specimen #2L LoadingSpecimen #1L Loading


14

Specimen #1L at 29.2 kips

Behavior at Ultimate Load

Punching Shear Failure

Specimen #2L at 23.7 kips

Behavior at Ultimate Load

Punching Shear Failure


15

Vertical Displacement

Specimen #1L Specimen #2L

2.5 6.5 10.5 11.5 12.5 13.5 14.5 15.5 16.5 20.5 24.50

0.1

0.2

0.3

0.4

0.5


Dis

plac

emen

t (in

.)

26.2k

24.2k

28.1k

29.2k

22.6k

2.5 6.5 10.5 11.5 12.5 13.5 14.5 15.5 16.5 20.5 24.50

0.1

0.2

0.3

0.4

0.5


Dis

plac

emen

t (in

.)

20.4k

16.0k

22.4k

23.7k

18.2k

Distribution Length


16

Lower Punching Shear

Upper Punching Shear


17

Nonsymmetrical Failure

Conclusions

• Diagonal tension joint failure (15ft and 3ft strip specimens)• Concrete failure rather than reinforcement anchorage in overhang• Only applicable for short bridge lengths (< 30 ft)

• Punching shear failure (27ft specimens)• Punching controls prior to forming barrier mechanism (110 kips vs 150 kips)• Consistent with actual failures

• Research suggests overhang reinforcement not critical• Punching shear governs design• Large distribution length (10Lt)• Reinforcement can be reduced in overhang


18

Recommendations

• Design overhang for vertical loads (Case 2 and 3)• If lateral force considered:

• Design for lesser of:• Punching Shear Strength

• Yield Line Strength

• Consider distribution length as 10Lt

Questions?

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