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Index - Optimized Sections for High-Strength Concrete Bridge Girders--Effect of Deck Concrete Strength, October 2006 - FHWA-HRT-05-058
For more than 25 years, concretes with compressive strengths in excess of 41 megapascals (MPa) (6,000 pounds per square inch (psi)) have been used in the construction of columns of highrise buildings. While the availability of high-strength concretes was limited initially to a few geographic locations, opportunities to use these concretes at more locations across the United States have arisen. Although the technology to produce higher-strength concretes has developed primarily within the ready-mix concrete industry for use in buildings, the same technology can be applied in the use of concretes for bridge girders and bridge decks.
The durability of concrete bridge decks has been a concern for many years, and numerous strategies to improve the performance of bridge decks have been undertaken.Many of the factors that enable a durable concrete to be produced also result in a high-strength concrete. Consequently, if a concrete for a bridge deck to be durable, it will probably also have a high compressive strength.This report contains an evaluation of the effect of high-performance concrete on the cost and structural performance of bridges constructed with high-performance concrete bridge decks and high-strength concrete girders. Several areas with the potential for improved structural performance through the use of high-performance concretes are investigated. This report should also assist designers and owners in recognizing that the use of high-performance concrete in bridges has advantages beyond those of improving durability.
FHWA-HRT-05-058
Optimized Sections for High-Strength Concrete Bridge Girders–Effect of Deck Concrete Strength
Evaluation, 1995–1997
Contracting Officer's Technical Representative: Joseph L. Hartmann, HRDI-06
This report contains an evaluation of the effect of high-performance concrete on the cost and structural performance of bridges constructed with high-performance concrete bridge decks and high-strength concrete girders. Bridge designers and owners are the main audience.
High-Performance Concrete, Girders, Concrete Bridge Decks
For over 25 years, concretes with specified compressive strengths in excess of 41 MPa (6,000 psi) have been used in the construction of columns of highbrows. While the availability of the high-strength concretes was limited initially to a few geographic locations, opportunities have developed to use these concretes at more locations across the United States. As these opportunities have developed,material producers and contractors have accepted the challenge to produce concretes with higher compressive strengths.
In the precast, prestressed concrete bridge field, a specified compressive strength of 41 MPa (6,000 psi) for bridge girders has been used for many years. However,strengths at release have often controlled the concrete mix design so that actual strengths at 28 days were often in excess of 41 MPa (6,000 psi). It is only in recent years that a strong interest in the utilization of concrete with higher compressive strengths has emerged. This interest has developed at a few geographic locations for specific projects in a manner similar to the development in the building industry.
In parallel with an increased interest in the use of high-strength concretes in bridge girders,the use of high-performance concretes in bridge decks has also been receiving increased attention as a means of improving durability. High-performance concretes provide higher resistance to chloride penetration, higher resistance to deicer scaling, less damage from freezing and thawing, higher wear resistance, and less cracking. Many of the methods used to increase the durability of concrete result in a concrete that has a higher compressive strength. However, the higher concrete strength is rarely considered because the design of prestressed girders is controlled by service load stresses caused by dead load, live load, and impact.
This report contains an evaluation of the effect of high-performance concrete on the cost and structural performance of bridges constructed with high-performance concrete bridge decks and high-strength concrete girders. Several areas with the potential for improved structural performance through the use of high-performance concretes are investigated. This report should assist designers and owners in recognizing that the use of high-performance concrete in bridges has advantages beyond those of improving durability.
The research described in this report was sponsored by the Federal Highway Administration as part of their program to encourage the greater use of high-performance concretes in bridges. The program includes analytical and experimental research as well as showcase projects. The authors believe that high-performance concrete represents a technology with great potential for improving the infrastructure of the highway system.
CHAPTER 3. TASK 2: ANALYSES OF FLEXURAL STRENGTH AND DUCTILITY
CHAPTER 4. TASK 3: ANALYSES OF PRESTRESS LOSSES AND LONG-TERM DEFLECTIONS
LONG-TERM DEFLECTIONS
TASK 3 CONCLUSIONS
Figure 1. Cross section of girder analyzed—PCI Bulb-Tee (BT-72). All dimensions are in millimeters (inches).
Figure 2. Cross section of girder analyzed—Florida Bulb-Tee (FL BT-72). All dimensions are in millimeters (inches)..
Figure 5. Optimum cost curves for a BT-72, 83 MPa.
Figure 16 (part 1). Cross section of series A girder (BT-72) analyzed in task 2. All dimensions are in millimeters (inches).
Figure 16 (part 2). Cross section of series B girder (BT-72) analyzed in task 2. All dimensions are in millimeters (inches).
Figure 16 (part 3). Cross section of series C girder (BT-72) analyzed in task 2. All dimensions are in millimeters (inches).
Figure 16 (part 4). Cross section of series D girder (BT-72) analyzed in task 2. All dimensions are in millimeters (inches).
Figure 17. Stress–strain curves for concrete used in BEAM BUSTER analysis.
Figure 18. Stress–strain curve for prestressing strand used in BEAM BUSTER analysis.
Figure 19. Moment–curvature relationships for BT-72, 41 MPa at a span of 24.4 m.
Figure 20. Moment-curvature relationships for BT-72, 83 MPa at a span of 24.4 m.
Figure 21. Moment-curvature relationships for BT-72, 41 MPa at a span of 44.5 m.
Figure 22. Moment-curvature relationships for BT-72, 83 MPa at a span of 53.3 m.
Figure 23 (part 1). Cross section of series A through D girders (BT-72) analyzed in task 3. All dimensions are in millimeters (inches).
Figure 23 (part 2). Cross section of series E girder (BT-72), 24.4 m (80-ft) span, analyzed in task 3. All dimensions are in millimeters (inches).
Figure 23 (part 3). Cross section of series E girder (BT-72), 44.5 m (146-ft) span, analyzed in task 3. All dimensions are in millimeters (inches).
Figure 23 (part 4). Cross section of series E girder (BT-72), 53.3 m (175-ft) span, analyzed in task 3. All dimensions are in millimeters (inches).
Figure 24. Variation of specific creep with compressive strength as published.
Figure 25. Variation of ultimate specific creep with compressive strength.
Figure 26. Variation of specific creep with age.
Figure 27. Prestressing strand stress versus time for varying girder concrete strength, 28-MPa deck strength, and 44.5-m span.
Figure 28. Prestressing strand stress versus time for 83-MPa girder concrete strength, 55-MPa deck strength, and varying spans.
Figure 29. Midspan deflection versus time for varying girder concrete strengths, 28-MPa deck strength, and 44.5-m span.
Figure 30. Midspan deflection versus time for 41-MPa girder concrete strength, varying deck concrete strengths, and 44.5-m span.
Figure 31. Midspan deflection versus time for 83-MPa girder concrete strength, 55-MPa deck strength, and varying spans.
Table 3. Deck design (English units).
Table 4. Deck design (SI units).
Table 9. Task 2 variables (SI units).
Table 10. Task 2 variables (English units).
Table 11. Calculated values of modulus of elasticity.
Table 12. Calculated stresses and strains at maximum moment (SI units).
Table 13. Calculated stresses and strains at maximum moment (English units).
Table 14. Calculated flexural strengths (SI units)
Table 15. Calculated flexural strengths (English units).
Table 16. Task 3 variables (SI units).
Table 17. Task 3 variables (English units).
Table 18. Values of creep used in PBEAM.
Table 19. Comparison of prestress losses (SI units).
Table 20. Comparison of prestress losses (English units).