Concrete Filled Steel Tube Bridge Pier Connections - An ABC Solution

Bijan Khaleghi State Bridge Design Engineer WSDOT

Dawn Lehman Professor, University of

Washington

Charles Roeder Professor, University of

Washington

Presentation Outline • Advantages of CFT for ABC • CFT Design and Construction • Concerns and Need for Research

• UW Research on CFST

Bridges for ABC • Flexural and Shear Design Expressions • Advantages of CFT for Seismic Applications • CFT to Cap and Footing Connections • CFT Implementation and Projects

Date, time and initials of last edit 2

Definition of CFT and RCFT Concrete filled tubes consist of a steel tubes,

filled with concrete, with or without Reinforcement Steel casing is used for Structural Capacity Structural welds at every splice and spirals Bond between Concrete and Steel Casing Connections to adjacent members

CFT and RCFT Specimens

An ABC and Practical Design Solution CFT columns can facilitate rapid construction CFT Could be Prefabricated for ABC projects CFT reduces project cost and time by elimination of

rebar cage, forming, less concrete CFT columns offer an efficient and economical

alternative to conventional RC columns. CFT allows the superior strength, stiffness and

seismic resilience CFT Connections could be designed for strength and

Extreme Limit States - Seismic CFT Offers Smaller columns and crossbeams

resulting in less mass for seismic design

Benefits of CFT and RCFT

CFT- An ABC & Practical Design Solution

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CFT eliminate the need for reinforcing steel and forming Reduce construction time and cost CFT Offers Smaller columns and crossbeams resulting

in less mass for seismic design

Challenges with CFT – Need for Research

• Lack of Design Guidance for Axial, Flexural and Shear Strength for CFT and RCFT

• Account for Strength and stiffness of steel casing in the analysis and design

• Connections to Pier Cap and Foundation for Strength and Extreme Limit States

• CFT & RCFT Embedment into Cap/Foundation • Bond between concrete and steel casing • Long term performance and longevity of CFT

Design Consideration: Lateral Loads

Ductility

Deep Foundation Lateral EQ Load

CFT Connections to Pier Cap and Foundation Suitable for Strength and Extreme Events

1. Flexural/Axial Design Expressions for CFT-RCFT for use in Bridge Components

2. Shear Design Expressions and Connection Details For CFT and RCFT for use in Bridge Components

UW CFT-RCFT Research Projects

Research on CFST Bridges for ABC

Professor Dawn Lehman & Professor Charles Roeder Max Stephens (Graduate Student Researcher) University of Washington

CFST Bridge System (Funding Agency)

CFST Component: (WSDOT, ARMY) ˃ Flexural Strength (6) ˃ Shear Strength (21) ˃ Deformation Capacity

Foundation Connection (17): (Caltrans, WSDOT, ARMY)

cap beam

column typ.

deck

foundation typ.

Cap Beam Connection (7) (Caltrans)

Welded Dowel (WD) Embedded Ring (ER)

Embedded Ring (ER)

RC Column to CFST Pile (ongoing with WSDOT)

Application of CFST to ABC

> Relative to RC construction – No formwork to construct,

tear down or store – Internal reinforcement not

required – Self-consolidating concrete – Smaller diameters than RC

columns > Relative to precast

– Lighter than precast columns; facilitate placement

– Length and diameters can easily vary within a structure

– Can be integrated with precast components including cap beams.

Photo Courtesy of MDT

Accelerated Construction Sequence

Accelerated Construction Sequence

Accelerated Construction Sequence

Accelerated Construction Sequence

Accelerated Construction Sequence

Accelerated Construction Sequence

Accelerated Construction Sequence

Welded Dowel (WD) Embedded Ring (ER)

Accelerated Construction Sequence

Accelerated Construction Sequence

CFST Components

Steel Tubes o Spiral Weld Tubes

o Economical, widely available, larger diameters and length than straight seam spiral weld tube

o Fabricated by running a coil of steel through a machine that spins the coil into a spiral

o Double submerged arc weld is used to seal the spiral; continuous x-ray of weld

o Weld provides mechanical bond

o Straight Seam Tubes o Thicker tubes available o More typically used

for driven piles o No mechanical bond;

low-shrinkage concrete or binding through bending required.

Comparison of Filled & Hollow Tubes

-15000

-10000

-5000

0

5000

10000

15000

-4% -3% -2% -1% 0% 1% 2% 3% 4%

Drift Ratio

Flex

ural

Str

engt

h (k

-in)

CFVST

HVST

CFVST Yield

CFVST Buckle

HVST Yield

HVST Buckle

• Increased Stiffness • Increased Strength • Increased Deformability • No loss of strength after buckling

Initial Buckling (~2.3% drift)

Initial Tearing (~2.7% drift)

Complete Tearing (3% drift)

B6KJM31TTBYW

Simple, filled-tube push-through tests and 3-point bending tests

t = ¼” d = 19 ½”

strain gage location typ.

rigid base support

air gap to allow slip

concrete fill length = 60”

applied load

welded wire gage location typ.

Applied Load 2.4m lb. UTM

Instrumented 20 in. Dia. Tube

Tube Concrete

Conventional

Low Shrinkage

Conventional

Low Shrinkage

Straight Seam

Spiral Weld

4-Test Matrix

Composite Action in CFST

Composite Action

Chemical Bond/ Adhesion

Mechanical Bond In Spiral Weld Tube

Mechanical bond of concrete In spiral weld tube

Shear Strength of CFST

> Current design expressions include steel tube only or treat CFST as an RC section with Vn = Vs + Vc

> Neither approach is correct > Both underestimate the shear strength by a factor of at

least two > Testing investigated: (a) aspect ratio, (b) D/t, (c)

concrete strength, (d) internal reinforcement ratio, (e) tail (anchorage) length, (f) axial load ratio

> Results show that CFST sections are very strong in shear.

21 tests on CFST specimens conducted. New expression proposed.

o Steel rupture

o Significant permanent shear deformation in steel

o Large localized deformation at bearing locations

o No visible flexural deformation in pure moment region

Example of Shear Failure of CFST

> a/D = 0.25 > D/t = 80 > f’c = 6 ksi

Post-Test Internal Concrete Damage

Connection Tests

CFST Column to Cap Beam Connections

Embedded Ring (ER) Connection

buckling visible

①

② ③

④

initiation of tearing

Response of ER Connection

① Failure mode and loss of lateral load initiated by ductile tearing of steel tube

② Buckling does not impact performance

③ Theoretical plastic moment capacity achieved

④ Axial load capacity maintained after tearing

②

③

Comparison of ER Specimen: With and Without Adequate Embedment

Le = 67% of Le,req

Debonded, Welded Dowel Connection

D (in) t (in) D/t P/Po Reinforcing Steel Fy (ksi) f’c (ksi) ρL(%) (fy/f’c)ρL

25.75 0.25 103 0.10 A706 Grade 60 68 7.7 3 0.3

Performance of WD Connection

① Achieved symmetric drifts of up to 9% with no degradation

② Theoretical plastic moment capacity of CFT achieved due to similar mechanical reinforcing ratio

7.5% Drift

Rocking

Reinforced Concrete (RC) Connection

Performance of RC Connection

north bar fracture

northwest and northeast bar fracture

south bar fracture

southwest and southeast bar fracture

o Failure mode fracture of reinforcing bars (~8% drift)

o Strength limited by reinforcing ratio and moment arm

12% Drift

Final State Grout damage

Key Considerations for ER Connection

① Annular Ring Dimensions ② Anchorage Depth of CFST ③ Punching Shear above Annular Ring ④ Cap beam reinforcing

1

3

2

Key Considerations for WD Connection

① Flange dimensions ② Dowel weld length ③ Anchorage depth of

headed bar ④ Dowel debonded

length ⑤ Punching shear

above headed dowels ⑥ Cap Beam

Reinforcing ⑦ Cap Beam Width

1

4

2

5

3

Original RC Pier

CFST Pier

Concrete Strength (ksi) 4.0 4.0

Steel Strength (ksi) 60.0 50.0

Diameter (in.) 72.0 42.0

Tube Thickness (in.) - 0.75

Concrete Area (in.2) 4000.0 1288

Steel Area (in.2) 101 97.19

Weight/ft of Pier (kips) 4.4 1.63

Total Pier Weight (kips) 231 85.4

Difference in Pier Weight 63% Reduction

Cold Water Creek Bridge

Comparison in Terms of Accelerated Bridge Construction

> ER connection offers several advantages in terms of ABC – No dowels or transverse reinforcing required – Precast cap can be placed directly onto column

> WD connection has several drawbacks – Welding and inspecting welds within the steel tube is

difficult – Temporary shoring required when using precast cap beam – Transverse reinforcing required around longitudinal dowels

> RC connection not conducive to ABC – Requires flexible reinforcing cage supported within the

steel tube – Temporary shoring required when using precast cap

From Research to Implementation • Design and Detailing Recommendations

for Bridge Design Manual • Material Specifications for Concrete and

Steel Casing • Bond Slip Requirements • Design Expressions for Flexure, Axial, and

Shear Resistance • CFT and RCFT Connections to Cap and

Foundation (Column, pile and Shaft)

Steel Casing Material Specifications • Steel Tubes:

– ASTM A252 Gr. 2 or 3

– ASTM A572 or A588

– API 5LGrade 42 or 52

• For primarily flexural members:

• For primarily to axial loading members: • Effective stiffness of CFT,

Welding and Inspection - AASHTO/AWS D1.1 Structural

longitudinal or spiral seam submerged-arc welded tube

Visual testing (VT) throughout Ultrasonic testing (UT) in high

stress areas Complete Joint Penetration

welds w/ backing

Design Recommendations: Flexural Capacity - Plastic Stress Distribution

CFT

RCFT

Shear resistance of CFST and RCFST: 𝑉𝑉𝑢𝑢 = ф𝑉𝑉𝑛𝑛 = ф𝑔𝑔4 𝑔𝑔1 0.6𝑓𝑓𝑦𝑦𝑔𝑔2𝐴𝐴𝑠𝑠 + 0.0316𝑔𝑔3𝐴𝐴𝑐𝑐 𝑓𝑓𝑐𝑐′

Design Recommendations: Shear Capacity

As = cross-sectional area of the steel tube Ac = area of concrete within the steel tube g1 = coefficient for the shear capacity of the steel tube = 2.0 g2 = coefficient for the effective shear area of steel tube = 0.5 g3 = coefficient for the effect on concrete strength in shear due to confinement from the steel tube = 3.0 g4 = coefficient for bond development between the concrete and steel tube = 1.0

Punching Shear

𝑉𝑉𝑢𝑢 = ф𝑉𝑉𝑛𝑛 = ф𝑔𝑔4 0.6𝑓𝑓𝑦𝑦𝐴𝐴𝑠𝑠 + 0.1𝐴𝐴𝑐𝑐 𝑓𝑓𝑐𝑐′

Bond Slip Requirements

Date, time and initials of last edit

47

US-Japan Workshop Tenpo-zan Ohashi Bridge

(Seismic retrofit - Foundation)

CFT-to-Cap Connections Connection design recommendations: a. Design of the annular ring b. Determination of the embedment depth c. A punching shear evaluation in the cap d. General design of the cap for flexure and shear An alternative to the annular ring - reinforcing cage to splice the CFT to the cap.

CFT-to-Cap Connections - Annular Ring Embedded flange connection: • Size the flange to develop the

casing, 16t • Embed the flange to prevent

pullout of the tension side • Provide cover to prevent

breakout on compression side • Cone Pullout Mechanism for

Cap Connections • Fillet welds to develop the full

tensile capacity of the tube

Column Connections: Column-to-Shaft Connection: • Column reinforcement extend into

the RCFT as required for noncontact lap splices.

• Contribution of steel casing varies from zero at the end of the tube to fully composite at the end of the transition zone equal to 1.0D.

• Column-to-cap Connection: o Cap width > 2D o Cap Thickness-Pullout and Punching Shear o Edge Distance

Nooksack River Bridge Project Highlights

• ABC and Practical Design Solution

• Deep Liquefaction

• CFT Pile Group

• Telescoping Piles 3.5 to 2 ft

• Partial depth Reinf Cage

• RCFT Cap Connection

• Butt weld Between Rings

• Ultrasonic & Visual test

Date, time and initials of last edit 52

Alaskan Way Viaduct Highlights

• ABC and Practical Design Solution

• Deep Liquefaction and Lateral Spread

• CFT Pile Group

• RCFT and CFT

• Partial depth Reinf. Cage

• Telescoping Piles 5 to 3 ft

• RCFT Cap Connection

Ebey Slough Bridge Highlights

• ABC and Practical

Design Solution

• RCFT and CFT - 5’ and 6’

• Partial depth Reinf Cage

• Liquefaction/Lateral

Spread • RCFT Cap Connection

Eastbound Nalley Valley Highlights

Date, time and initials of last edit 54

• ABC and Practical Design Solution

• CFT Pile-Column 3 ft dia.

• CFT Ring Connection to Cap

• Driven Pile-Column (no Reinf)

• Smaller column and Cap

Puyallup River project Highlights • ABC and Practical

Design Solution 2015 ABC Webinar

• Deep Liquefaction

• CFT Pile Group

• Partial depth bar cage

• 10 ft dia. RCFT and CFT

• RCFT Cap Connection

• • 1 2

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Future: CFT – RCFT Could be used in:

Accelerated Bridge Construction Projects Temporary Piers and Columns Bridge with Deep Foundation Sites where permanent casing is required

for caving soils Sites with Liquefiable soils where plastic

hinging is required Other applications as appropriate

Resources: • WSDOT BDM and UW Research Reports BDM - http://www.wsdot.wa.gov/publications/manuals/fulltext/M23-50/Chapter7.pdf UW Report-http://www.wsdot.wa.gov/Research/Reports/700/776.1.htm UW Report-http://www.wsdot.wa.gov/research/reports/fullreports/776.1.pdf

University of Washington Contacts: Research: Dawn Lehman: Delehman@uw.edu Research: Charles Roeder: Croeder@uw.edu WSDOT Contacts: Foundation: Anthony Mizumori MizumoA@wsdot.wa.gov Steel: Geoff Swett, SwettG@wsdot.wa.gov ABC: Jed Bingle, BingleJ@wsdot.wa.gov Bijan.Khaleghi@wsdot.wa.gov Thank You