1. Rapid Construction of Bridge Piers with Concrete Filled Tubes
Dawn Lehman and Charles Roeder
University of Washington

2. Introduction
CFT elements are fully composite members maximizing the benefits of the steel and concrete
CFT elements are not RC columns with steel jackets used to confine concrete piers to improve their performance

3. Seismic Damage of Bridge Piers
Steel is strong in tension and compression yet susceptible to buckling
Concrete is strong in compression yet susceptible to
shear and spalling

4. CFT Construction is a Solution
Advantages
Large Strength: compression, flexure, shear
Large Stiffness
Inherent Stability: permits use of high-strength steel
Reduced Labor relative to RC construction: formwork or reinforcing steel are eliminated
Limitations
Deformation capacity unknown
Strict D/t ratios (AISC)
Design methods limited and have not been validated
No standard connections; existing are complex

5. Use of CFT in Transportation
CFT Bridge Piers
CFT Piles and Caissons

6. Advantages of CFT for ABC
Reduced costs: labor and material savings.
Improved seismic performance, blast and collapse resistance
Design eliminates labor and time associated with formwork and reinforcement.
Use Self-Consolidating Concrete (SCC) reduces time associated with casting
Sustainably oriented design: reduced transportation requirements and energy consumption, use of recycled materials including steel and high-replacement cement concrete

7. Overview of Research Programs
Feasibility and development of CFT bridge piers using high-performance steel (US ARMY)
Experimental evaluation of components
Development and evaluation of foundation connection
Rapid construction of CFT bridge piers with high seismic performance (Caltrans)
Evaluation and design of foundation connection
Development and design of cap beam-to-column connection
Design of bridge foundations with steel casings (WashDOT)
Evaluation of steel-cased caisson strength and deformability
Sustainably–oriented ABC: use of high replacement cement concrete (TransNOW)

8. Overview of Research Programs
Phase
COMPONENT
TESTS
COLUMN
FOUNDATION
DESIGN
MODELS
COLUMN
CAP BEAM
Parameters
Embedment
Connection Type
Material Strengths
Axial Load
Future Work:
Connection Type
Geometry
Embedment
Engineering Properties
Influence of Bond
Impact of Weld Properties
Flexural Strength
Slenderness
Stiffness
ARMY
Caltrans
Caltrans
WashDOT
ARMY/Caltrans
Caltrans

9. Experimental Research: Component Tests

10. UW/US ARMY Study High-strength, low carbon-equivalent steel (70 ksi)
High-strength, low-shrinkage, self-consolidating concrete (10 ksi)
Spiral weld tube
Economical, widely available, larger diameters and length then straight seam spiral weld tube
Fabricated by running a coil of steel through a machine that spins the coil into a spiral
Double submerged arc weld is used to seal the spiral; continuous x-ray of weld

11. Engineering Properties of CFVST
Investigate engineering response of CFT components.
Engineering Properties
Stiffness
Strength
Deformability
Fatigue Resistance
Study Parameters
Bond (4/2)
Weld (3/0)

12. Test configuration 18 ft Instruments to monitor
local rotations, strains
Actuator to apply
Cyclic load
18 ft

13. Observed Response Initial Buckling (~2.3% drift)
Initial Tearing (~2.7% drift)
Complete Tearing (3% drift)

14. Comparison of Filled and Hollow Tubes

15. Effect of Bond Condition
Greased
Reference

16. Effect of Weld Strength

17. Experimental Research: Column-to-Foundation Connection

18. Tests on CFT Connections
Army Study: High-strength (70 ksi) Vanadium Steel
Embedment depth
Type of connection: monolithic and isolated
Foundation boundary conditions
Punching shear capacity
Caltrans study: Further study of connection for CFT typical steel (50 ksi) and concrete (6 ksi) strength.
Type of tube: spiral and straight seam weld
Tube geometry (D/t ratio)
Axial Load Ratio

19. Specimen Geometry 20” diameter ¼” thick wall 72 in. column
Annular ring
Embedded aD
Into Adjacent
Component

20. Design of Isolated Connection
Isolation of Structural and Reinforcing Steel Trades
Build foundation cage
Install corrugated metal pipe
Cast foundation
Install and grout tube
Cast column
CORRUGATED
METAL PIPE
FOUNDATION

21. Constant axial load (10%P0)
Test Configuration
Constant axial load (10%P0)
Test Specimen
Cyclic Lateral Load

22. Observed Behavior: 0.6D Embedment
Interface gap: 2.5% drift
Bisecting cracks: 0.75% drift
Final state: 8% drift
Footing uplift: 4% drift

23. Response: 0.6D Embedment V(Mp) pull-out
Max Force = k Drift = 2.4%

24. Observed Behavior: 0.9D Embedment
Limited footing damage: 2.5% drift
Tube buckles: 4% drift
Ductile tearing: 6% drift

25. Isolated vs. Monolithic Connection
V(Mp)
Monolithic Connection
Isolated Connection

26. 50-ksi Straight Seam Weld Tube

27. 50-ksi Spiral Weld Tube

28. Spiral vs. Straight Seam Weld Tubes

29. Comparison Summary
Specimen
Le (in)
Strength
Connection type
Drift
M/Mp
Failure Mech.
III 18
70ksi
Embedded
1.2%
1.07
2.4%-4.3%*
Tearing 6% V
1.0%
1.04
4.1%
1.4
7.1% VI 15
Grouted
0.95
3.11%
1.27
6.1%
50-I 16
50ksi
1.08
3.2%
1.35
11.3%
50-II
15.5
0.9%
0.99
2.2%
10.4%
50-III
0.8%
0.92
1.4%
1.32
7.4%
*Strength Deterioration occurred at 2.4%. Visible bucklng occurred at 4.3%
Embedment of D achieved plastic strength and drifts of 6-10%
Lower strength steel tubes achieved higher drifts ~ 7.4% spiral, 10.4% straight seam
Failure mechanism is tearing, initial buckling does not reduce capacity.

30. Design Methods

31. Design Methods Flexural Strength Stiffness Impact of D/t Ratio
Connection

32. Evaluation of Design Methods
Circular Specimens Subjected to Flexure or Combined Loading
All Specimens Larger than 4 inches in Diameter
122 Test Specimens from 16 Data Sets
CFT-Footing Connection Tests
Beam-Column Tests
Eccentrically Loaded Tests
Flexural Tests

33. Plastic Stress Distribution Method
Assume Steel is at Yield in Tension & Compression
Assume Concrete Stress Block of 0.85f’c f’c
External Axial Load is Applied at Centroid

34. Evaluation using Experimental Data

35. Evaluation of Flexural Strength

36. Effective Stiffness Effective Stiffness Expressions
AISC Effective Stiffness For Concrete-Filled Tubes
ACI Effective Stiffness For Composite Members
Proposed Effective Stiffness For Composite Members

37. Effective Stiffness Evaluation
AISC Expression: Over-Predicts Initial Stiffness
ACI, Combined AISC-ACI Expression: Under-Predict EI
Proposed Expression: Moves Average to 1.0 with same Std. Dev.
Experimental Stiffness Comparison of All Specimens
EIexperimental / EIeff_predicted
Research Data Set
Mean
Min.
Max.
Std. Dev.
AISC
0.81
0.50
1.23
0.20
ACI
1.27
0.76
2.00
0.33
Combined AISC-ACI
1.14
0.71
1.81
0.27
Proposed Expression
1.00
0.70
1.57
0.22

38. Effect of D/t Ratio Concern about larger D/t ratio:
Reduced composite action?
Premature buckling?
Reduced strain hardening?
FEM study conducted
Validation using experimental results
Simulation of bending and axial CFT specimens

39. Validation
Bending
Compression

40. Flexural Strength
Effect of strength ratio of concrete & steel has more significant effect on CFT under bending than D/t ratio.

41. Effective Stiffness AISC Roeder
AISC provides good indicator of EI(0.1) [EI form 0% to 10% of My] while Roeder et al. (2010) gives a good results of EI(0.9)

42. Anchorage
Cone
Pullout
Failure
Concrete
Push-thru
Failure

43. Proposed Expression

44. Summary
CFT offers rapid construction and structural integrity for seismic loading
Spiral tubes must have matching weld must be used; weld offers mechanical bond. Composite action insured through binding
Developed connection offers reduced damage and increased drift relative to RC
Design methods are simple yet effective to predict flexural capacity, strength, connections

45. Thank You