Non-metallicGFRP Bar and Macrofiber

Reinforced Concrete Bridge DecksStatic and Fatigue Flexural Testing

Utah State Universitywith support from

Owens Corning

Research Significance

The 2017 ASCE report card stated that as of 2016, 9.1% of bridges were structurally deficient. Complete repairs would reach upwards of $123 billion.*

*American Society of Civil Engineers (2017). 2017 Infrastructure Report Card

Research Significance

As of 2002, the annual direct cost of steel corrosion for bridge decks was approximately $2 billion.*

Corrosion of Epoxy-Coated Rebar – Photo Courtesy of INDOT (Frosch 2014)

*Koch, G. H., Brongers, M. P. H., Thompson, N. G., Virmani, Y. P., & Payer, J. H. (2002). Corrosion Cost and Preventive Strategies in the United States. United States. Federal Highway Administration.

Research Significance

There is a need for innovations to mitigate corrosion and bolster bridge infrastructure.

Bridge decks without steel-reinforcement have the potential to reduce life cycle costs

GFRP Rebar Tied for Bridge Deck Application

Project Summary

Three types of bridge deck sections tested in static flexure & flexural fatigue:

Steel Reinforced (Control using FDOT Standards)

Glass Fiber Reinforced Polymer (GFRP) Reinforced

Hybrid GFRP with AR-glass FRP macrofibers at 15 lbs/cubic yard dosage

Next the punching shear specimens of each type will be tested statically and under fatigue loading.

Static FlexureTraditional bridge deck design method is often a flexural design on a unit

strip of deck

Flexural mechanics of any new material are imperative to a design engineer

AASHTO Equivalent Strip Method (AASHTO 2012)

3 Types – Steel, FRP Bar & Macrofiber, FRP Bar-only

GFRP with Macrofibers#6 @ 8” o.c. Transverse#6 @ 13” o.c. Distribution

Steel-only Reinforcing #5 @6” o.c. Transverse#5@ 8” o.c. Distribution

GFRP-only#6 @ 6” o.c. Transverse#6 @ 8” o.c. Distribution

Steel-only Decks

Steel-only decks

Property Result

Concrete Compressive Strength (f ’c): 5,400 psi

Average Tested Moment Capacity: 97.2 k-ft

Unfactored Design Capacity (Mn): 64.9 k-ft

Factored Moment Demand (Mu): 51.6 k-ft

Deflection at Failure: 2.4 in

Comments:(1) Outstanding post-cracking ductility(2) Equally-spaced cracks throughout constant moment region(3) Tested capacity far exceeded design capacity and demand due to strain-hardening of steel

GFRP Bar-only Decks

GFRP Bar-only DecksProperty Result

Concrete Compressive Strength (f ’c): 6,800 psi

Average Tested Moment Capacity: 146.8 k-ft

Unfactored Design Capacity (Mn): 102.6 k-ft

Factored Moment Demand (Mu): 51.6 k-ft

Deflection at Failure: 3.6 in

Comments:(1) Brittle, sudden failure with almost no post-peak behavior(2) Concrete crushed prior to rupture of the GFRP bars as designed(3) Actual capacity of the deck was nearly 3x greater than the design demand(4) Spreader beam was eliminated to ensure flexural failure

GFRP Bars with AR-Glass FRP Macrofiber

43 mm AR-Glass Macrofibers

GFRP Bar Layout Prior to Casting

Test Set-up

GFRP Bars with AR-Glass FRP MacrofibersProperty Result

Concrete Compressive Strength (f ’c): 6,340 psi

Average Tested Moment Capacity: 119.5 k-ft

Unfactored Design Capacity (Mn): 93.6 k-ft

Factored Moment Demand (Mu): 51.6 k-ft

Deflection at Failure: 4.5 in

Comments:(1) Superplasticized fiber-reinforced concrete was very workable(2) More ductile than GFRP-only with post-peak deflections and residual strength(3) Dispersion of fibers after failure appeared even and uniform(4) Exceptional crack distribution prior to crushing of concrete

Summary of Static Testing

Figure 1 – Moment vs. Displacement for Static Flexure Tests

Summary of Static Testing

Static testing on 3 types of bridge decks:

Steel-only, GFRP-only, and GFRP with FRP macrofibers.

At the ultimate load, several behavior trends were observed:

While the GFRP decks were more brittle, adding fibers provided substantial ductility prior to and after cracking

At concrete crushing strain, GFRP with macrofibers experienced 92% and 24% greater deflections than the steel decks and GFRP-only decks, respectively. Therefore, extra warning prior to failure.

Summary of Static Testing

The crack distribution of the GFRP-only and steel-only decks were similar, but the GFRP with fibers had much wider cracks and larger deflections prior to failure

GFRP with Fibers just before collapse#6 @ 8” o.c. Transverse#6 @ 13” o.c. Distribution

GFRP-only just before collapse#6 @ 6” o.c. Transverse#6 @ 8” o.c. Distribution

Reference: Steel-only Reinforcing #5 @6” o.c. Transverse#5@ 8” o.c. Distribution

Summary of Static Testing

Static testing shows that at the strength limit state, FRP composite macrofiber added to a deck with GFRP bars is a viable reinforcing option

Fatigue Loading

Fatigue is an important parameter for bridge decks since they will experience millions of cycles over their life span

AASHTO doesn’t require any special fatigue detailing or design for concrete bridge decks, but it is important to understand the behavior mechanisms before adopting new materials

Fatigue Loading

The scaled maximum load required to induce the fatigue limit state moment was 13.24 kips.

10% min. load (1,324 lbs) was maintained to ensure contact between MTS Ram and plates.

http://www.mts.com/cs/groups/public/documents/library/dev_002093.pdf

AASHTO Design Truck (AASHTO 2012)

MTS Hydraulic Actuator used to apply the fatigue loads

Fatigue Loading Criteria

Live Load deflection limit from AASHTO*:

L/800

Max crack width recommendations from AASHTO** at service moment:

0.02 in (0.5 mm) for GFRP decks***

Decreases to 0.013 in (0.33 mm) for Steel

*AASHTO. (2012). AASHTO LRFD bridge design specifications. American Association of State Highway and Transportation Officials, Washington, DC.

**Yost, J., Dinehart, D., Gross, S., Reilly, P., & Reichmann, D. (2015). Fatigue behavior of GFRP and steel reinforced bridge decks designed using traditional and empirical methodologies. Bridge Structures, 11(3), 87–94.

***AASHTO. (2018). AASHTO LFRD Bridge Design Guide Specifications for GFRP-Reinforced Concrete. American Association of State Highway and Transportation Officials, 121.

Fatigue Figures – 1 Million Cycles - Deflection

GFRP-only is barely outside of the limit.

The other two decks are within the limit.

Due to testing setup, these values will be much smaller in service.

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Fatigue Figures – 1 Million Cycles – Crack Width

This figure shows how much a crack opens as the AASHTO truck goes over the deck for 1 million cycles

Note AASHTO limit for GFRP is 0.02” at top of chart

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Fatigue Figures – 1 Million Cycles – Crack Width

This figure shows the absolute max crack under live load for 1 million cycles

All decks are well within the AASHTO recommended criteria

Steel-only decks in FatigueProperty Result

Concrete Compressive Strength (f ’c): 5,400 psi

Post-Fatigue Tested Moment Capacity: 99.8 k-ft

Unfactored Design Capacity (Mn): 64.9 k-ft

Factored Moment Demand (Mu): 51.6 k-ft

Deflection at Failure: 2.4 in

Comments:(1) Very similar results to static testing with no fatigue loading(2) Impressive post-peak performance and toughness

GFRP Bar-only decks in Fatigue

Property Result

Concrete Compressive Strength (f ’c): 7,400 psi

Post-Fatigue Tested Moment Capacity: 149.8 k-ft

Unfactored Design Capacity (Mn): 102.6 k-ft

Factored Moment Demand (Mu): 51.6 k-ft

Deflection at Failure: 3.9 in

Comments:(1) Slightly higher moment capacity than static testing without fatigue cycles(2) Slightly larger deflection than static test(3) Bottom of concrete deck fell off indicating a possible bond failure at ultimate load

GFRP Bars with AR-Glass FRP Macrofibers in FatigueProperty Result

Concrete Compressive Strength (f ’c): 6,340 psi

Post-Fatigue Tested Moment Capacity: 135.4 k-ft

Unfactored Design Capacity (Mn): 93.6 k-ft

Factored Moment Demand (Mu): 51.6 k-ft

Deflection at Failure: 4.8 in

Comments:(1) Less post-peak behavior than static test, but higher moment capacity(2) Slightly larger deflection than static test at failure(3) Deck was tested with single load at mid-span to force a flexural failure

Summary - Post-Fatigue Static Flexure

Figure 5 – Moment vs Displacement – Static Flexure after Fatigue

Summary – Service Limit State (Deflection)

All of the decks met the AASHTO peak live load deflection criteria except for GFRP-only, which exceeded the limit by only 0.0019 inches

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

Steel GFRP GFRP with Fibers AASHTO Limit

AASHTO Max Deflection

Summary – Service Limit State (Cracking)

All decks met the AASHTO requirement for cracking

Summary – Service Limit State in Fatigue

The steel and GFRP with FRP macrofibers decks experienced smaller live load deflections than the GFRP-only decks

Actual deflections and crack widths would be smaller on a deck in service due to higher stiffness from both lateral restraint and different aspect ratios

Summary – Strength Limit State in Fatigue

One million cycles of fatigue loading had an almost negligible effect on the static moment capacity of all three decks.

Due to the environmental factors and high resistance factors for GFRP, the design for decks with GFRP bars was very conservative for the strength limit state.

GFRP deck with macrofibers experienced greater deflections at failure both before and after fatiguing than the steel or GFRP-only decks.

Conclusions

Corrosion mitigation is imperative in bridge deck applications

Bridge Decks with discrete FRP composite bars and FRP macrofiber reinforcement are shown to be cost-neutral with epoxy-coated steel from preliminary cost analysis

Both the strength and the service limit state requirements set forth by AASHTO were met by the proposed composite bridge decks

Future Research Needs

Current project:

Punching shear specimens

Casting has begun

Research that examines fatigue behavior of Fiber Reinforced Concrete (FRC) is scarce for structural scale applications

Fatigue resistance of structural macrofiber reinforcement

Fatigue of discrete reinforcing bars and fibers (hybrid members)