Press-Brake-Formed Steel Tub Girders: Research Update

Steel Bridge Task Force Presentation: January 25, 2017

Gregory K. Michaelson, Ph.D.

Marshall UniversityWeisberg Division of Engineering

michaelson@marshall.edu

mailto:michaelson@marshall.edu

Outline• Proposed System Details & Design Methodology• Experimental Testing

– Single Composite Girders– Modular Composite Units

• Assessment of Composite Flexural Capacity• Implementation & Field Investigations (Amish Sawmill Bridge)• Current & Future Efforts

Proposed System• Bridge Technology Center:

– Modules with steel press-brake tub girders

• Galvanized or weathering

– Modules are joined using UHPC longitudinal closure pours

– Modules can be shipped to site pre-topped or with a variety of deck options

Design Methodology• Goal:

– Utilize standard plate widths• 84”, 96”, etc.

– Maintain 1:4 web slope, “5t” radii, and 6” btf

• Consistent w/ AASHTO Spec.

– Optimize girder dimensions to attain maximum capacity

Design Methodology (cont’d)• Resulting girder depths:

– 60” plate: d = 12”– 72” plate: d = 17”– 84” plate: d = 23”– 96” plate: d = 26”– 108” plate: d = 30”– 120” plate: d = 34”

• All composite section propertiesare available upon request.

Experimental Testing• Testing was conducted on composite, noncomposite, and modular flexural specimens:

– 84” × 7/16” PL– Dimensions shown below:

Experimental Testing (cont’d)

Analytical Methods• FEA was completed using Abaqus

– S4R shell elements were employed to simulate the girder and deck– von Mises material laws governed steel behavior– A smeared cracking model incorporating tension stiffening was employed for concrete

behavior

Analytical Methods (cont’d)• Using strain-compatibility methods,

estimates of girder capacity were obtained:– Steel was assumed to behave

linearly until Fy– Concrete in compression was

assumed to have a uniform stress of 0.85 fc’

– Neutral axis depth was iterated until equilibrium was attained.

• Moments were then summed to obtain capacity.

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5

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-20000 0 20000

Dep

th A

long

Cro

ss-S

ectio

n (in

)

Strain × 106

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-10 0 10 20 30 40 50 60

Dep

th A

long

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ss-S

ectio

n (in

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Stress (ksi)

Modular (UHPC) Fatigue Lab Test• To date, tests on singular tub-girder units (both

in their composite and noncomposite states) have been completed.– Recent testing efforts have been focused on

assessing the concept’s system-level behavior.

• Modular test goals:– Assessing best practices for closure pours.– Assess the performance of:

• UHPC Closure Pours• Press-brake-formed tub girders under fatigue loading.

Modular Unit Specimen Construction

Modular Unit Specimen Construction (cont’d)

Modular Unit Fatigue Loading (67.43 kip, 0.75 Hz Frequency)

Experimental Test Results (Modular Unit, Service II Loading)• Service II Live Loading (max bottom flange stress ≈ 13 ksi):

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0 10 20 30 40 50 60 70 80 90 100

Back

-Cal

cula

ted

Verti

cal L

oad

(kip

)

Applied Vertical Load (kip)

Q-Q Plot (Complete Test)

N = 0

N = 500,000

N = 1,000,000

N = 1,500,000

N = 2,000,000

N = 2,100,000

N = 2,200,000

N = 2,300,000

N = 2,500,000

N = 2,700,000

N = 2,800,000

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0 50 100 150 200 250 300 350 400 450 500

Appl

ied

Load

(kip

)Microstrain

Bottom Flange Evaluation

N = 0

N = 500,000

N = 1,000,000

N = 1,500,000

N = 2,000,000

N = 2,100,000

N = 2,200,000

N = 2,300,000

N = 2,500,000

N = 2,700,000

N = 2,800,000

Loaded Girder

Unloaded Girder

Experimental Test Results (Strength Loading)• Once fatigue loading was completed, the

specimen was loaded to (and well past) the strength limit state.

– As shown, the specimen performed sufficiently and linearly through the Strength I limit state,

• Results:– This series of experiments indicate that modular

press-brake-formed tub girders will perform adequately through their intended service life!

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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Appl

ied

Load

(kip

)

Vertical Deflection (in)

Strength I Test Results

Load = 126.5 kip

Composite Section Capacity• In order to evaluate the applicability

of AASHTO Specifications, a parametric matrix of composite girders was developed (resulting in 900 girders):– 18 girders (previously described)– 50-ksi and 70-ksi steel employed– 25 deck options

• 5 deck thicknesses (7” to 11” in 1” increments)

• 5 deck widths (defined based on out-to-out width of the girder

( )

( )

AASHTO

Proposed

0.1

1.07 0.7 0.1 0.42

0.1

1.025 0.25 0.1 0.42

p p t

pnp t p t

t

p p t

pnp t p t

t

M D DDM

M D D DD

M D DDM

M D D DD

≤= − < ≤

≤= − < ≤

Feasibility Assessments• Assessments were conducted according to AASHTO:

– Spans ranged from 20’ – 140’ in 5’ increments– The following limit states were evaluated:

• Strength I (for moment and shear):– 1.25 DC + 1.50 DW + 1.75 (LL+IM)

• Service II (for moment):– 1.00 DC + 1.00 DW + 1.30 (LL+IM)

• Live load deflection:– Limited to L/800

Standardization• Based on plate availability and the

feasibility of the modular system, the following standardized girders are proposed:– PL 72” × 1/2”

• Applicable for spans up to 40 feet

– PL 96” × 1/2”• Applicable for spans up to 60 feet

– PL 120” × 5/8”• Applicable for spans up to 80 feet

– Double PL 60” × 1/2”• Applicable for spans up to 65 feet

Amish Sawmill Bridge• Brian Keierleber, P.E., was awarded $350,000 from

FHWA IBRD Program to replace the Amish Sawmill Bridge at 1358 Dillon Avenue in Fairbank, Iowa.– The grant laid the groundwork to complete the first

installation of the proposed modular press-brake-formed steel tub girder system in the U.S.

• Construction on the Amish Sawmill Bridge began in the late summer of 2015 and was completed in December 2015

Amish Sawmill Bridge (cont’d)• A live load field test on the structure was completed in

June of 2016.

• Goals:– Assess field performance of the press-brake-formed tub

girder system.– Determine live load distribution characteristics of both

press-brake-formed tub girders as well as that of steel structures with integral abutments.

Amish Sawmill Bridge (cont’d)

Amish Sawmill Bridge (cont’d)• A total of 5 individual truck runs

were completed:

– These were identified to maximize load placements on Girders 1 and 2 (due to symmetry).

– In addition, combining Runs 1/4 and 2/5 can simulate multiple-lane-loading conditions.

• For each truck run, readings were taken at each panel point.

Amish Sawmill Bridge (cont’d)• Results from FEA were compared against experimental data:

– Specifically, a comparison of live load distribution factors was conducted.

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Expe

rimen

tal D

F

Analytical DF

DF Summary

Single Truck Run Multiple Truck Runs

R² = 0.91

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Girder 1 Girder 2 Girder 3 Girder 4

Dis

tribu

tion

Fact

or

Truck Run #1 Average DFs

FEA Experimental

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Girder 1 Girder 2 Girder 3 Girder 4

Dis

tribu

tion

Fact

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Truck Run #3 Average DFs

FEA Experimental

Current & Future Efforts• Modular system behavior:

– Refined 3D finite element modeling

Future testing at WVU to assess the fatigue performance of hot-dipped galvanized girders vs. weathering steel girders.

Current & Future Efforts (cont’d)• Noncomposite section capacity

– Governing buckling modes of the girders were determined using CUFSM:• Operates through use of the constrained finite strip method• Available from JHU (Schaefer and Ádány 2006)

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Mcr

/ My

Half Wavelength (in)

PL 84" × 7/16"

1.52 My

Current & Future Efforts (cont’d)• Three upcoming structures:

– 2 in WV, 1 in OH• OH project scheduled to begin construction

in April 2017• Current status (WV):

– Bridges have been programmed (allocated for funding)

– ROW purchases are underway– Alignment is complete– Core boring logs obtained– Precast foundation elements selected– Projects are scheduled for construction in

the Summer/Fall of 2017.

Current & Future Efforts (cont’d)• Refinement of cold bending limits in

AASHTO Construction Spec.:

– Previous versions of the specification (2010) limited bend radii to 1.5t.

• Limits were updated in 2012 and became much more stringent.– Current research efforts are intended to

assess fatigue performance of cold bent regions.

– FHWA-PROJ-13-0038 - Fracture Resistance of Cold Bent Steel

Questions?

Thank You!

michaelson@marshall.edu(304) 696-5606

mailto:michaelson@marshall.edu

Press-Brake-Formed Steel Tub Girders: Research Update��Steel Bridge Task Force Presentation: January 25, 2017OutlineProposed SystemDesign MethodologyDesign Methodology (cont’d)Experimental TestingExperimental Testing (cont’d)Analytical MethodsAnalytical Methods (cont’d)Modular (UHPC) Fatigue Lab TestModular Unit Specimen ConstructionModular Unit Specimen Construction (cont’d)Modular Unit Fatigue Loading (67.43 kip, 0.75 Hz Frequency)Experimental Test Results (Modular Unit, Service II Loading)Experimental Test Results (Strength Loading)Composite Section CapacityFeasibility AssessmentsStandardizationAmish Sawmill BridgeAmish Sawmill Bridge (cont’d)Amish Sawmill Bridge (cont’d)Amish Sawmill Bridge (cont’d)Amish Sawmill Bridge (cont’d)Current & Future EffortsCurrent & Future Efforts (cont’d)Current & Future Efforts (cont’d)Current & Future Efforts (cont’d)Questions?