TECHBRIEF Structural Behavior of a 2nd

Generation UHPC Pi-Girder

FHWA Publication No. of this TechBrief: FHWA-HRT-09-069 

FHWA Contact: Ben Graybeal, HRDI-06, 202-493-3122, 

benjamin.graybeal@dot.gov 

This document is a technical summary of the unpublished 

Federal Highway Administration report, Structural Behavior 

of a 2nd Generation Ultra-High Performance Concrete 

Pi-Girder, available only through the National Technical 

Information Service (NTIS).

NTIS Accession No. of the report covered in this TechBrief: 

PB2009-115496

Objective

This TechBrief highlights the results of a research program 

that evaluated a 2nd generation ultra-high performance 

concrete (UHPC) pi-girder cross section developed for use

in short- and medium-span highway bridge applications.

Introduction

UHPC is an advanced cementitious composite material 

which has been developed in recent decades. Compared 

to more conventional concrete materials, UHPC tends to 

exhibit superior properties such as exceptional durability, 

high compressive strength, usable tensile strength, and 

long-term stability.(1,2)

This experimental investigation focused on the structural 

behavior of a newly developed highway bridge girder 

cross section, the pi-girder. This girder was developed 

and optimized to exploit the advanced mechanical and 

durability properties of UHPC. Full-scale prestressed girders 

were fabricated, and structural testing was completed on 

these girders to investigate critical structural behaviors. 

Through this work, topics related to the design and the 

fabrication of the pi-girder were also addressed.

UHPC

Advances in the science of concrete materials led to the 

development of the next generation of cementitious 

Research, Development, and 

Technology

Turner-Fairbank Highway 

Research Center

6300 Georgetown Pike

McLean, VA 22101-2296

www.tfhrc.gov
2

materials, namely UHPC. As a class, these 

concretes tend to contain high cementitious 

material contents, low water-to-cementitious 

material ratios, compressive strengths 

above 21.7 ksi (150 MPa), and sustained 

tensile strength resulting from internal 

fiber reinforcement. Table 1 presents a 

select set of material properties for the 

type of UHPC investigated in this study.(1)

2nd Generation UHPC Pi-Girder

The advanced properties of UHPC provide 

opportunities for the development of new 

structural forms focused on addressing 

any number of important transportation 

infrastructure issues. Straightforward topics 

such as creating longer lasting bridges 

through enhanced durability and allowing 

for the spanning of longer distances with 

shallower superstructures can be addressed 

through the use of UHPC. In a systematic 

sense, UHPC also presents the opportunity 

to create new structural forms which facilitate accelerated construction and rapid 

renewal of the highway infrastructure.

Development of a UHPC decked girder member prototype was initiated during the early 

stages of the Federal Highway Administration’s (FHWA) UHPC research program. 

Results from the full scale fabrication and 

testing of this prototype girder are presented in Structural Behavior of a Prototype 

Ultra-High Performance Concrete Pi-Girder.

(4)

These results led to the refinement of the 

pi-girder solution and the development of 

a 2nd generation pi-girder component. 

The basic cross sectional shape of this 2nd 

generation UHPC pi-girder is similar to the 

prototype; however, modifications to ease 

fabrication, simplify construction, and add 

structural capacity have been implemented. 

The cross section modifications include increased deck thickness and width, increased 

web thickness, decreased web spacing, and 

rounded reentrant corners (see figure 1). 

Overall, this girder is a modular component 

designed to span up to 87 ft (26.5 m). Each 

Table 1. UHPC material properties.

Property Value

Unit weight

156 lb/ft3

(2,500 kg/m3)

Modulus of elasticity

7,600 ksi 

(52,400 MPa)

Compressive strength

28.0 ksi 

(193 MPa)

Post-cracking tensile 

strength

1.0 to 1.5 ksi 

(6.9 to 10.3 MPa)

Chloride ion 

penetrability 

(ASTM C1202)(3) Negligible

Figure 1. A 2nd generation UHPC pi-girder cross section. 

5.3 inches

(133 mm)

33 inches

(838 mm)

100 inches (2,540 mm)

4.1 inches

(105 mm)

3.2 inches

(81 mm)

50.5 inches (1,283 mm)
3

girder is 100 inches (2.54 m) transverse to 

traffic and 33 inches (0.84 m) deep. It can 

also be prestressed by up to 16 strands in 

each bulb.

Test Program

Testing the pi-girder prototype demonstrates that the primary flexure and shear 

behaviors of this girder are consistent with 

a line girder analysis and can be predicted 

through the use of basic engineering 

principles. As such, these behaviors were 

not explicitly investigated in the testing 

of the 2nd generation component. The 

structural testing completed for this study 

focused on the transverse flexural response 

of the girder when subjected to monotonically increasing simulated wheel loads. 

Two 25-ft (7.6-m)-long prestressed girders 

were fabricated at a conventional precast 

girder production plant and then shipped to 

FHWA’s Turner-Fairbank Highway Research 

Center. The transverse flexural capacity of 

the girder deck between the webs, as well 

as the longitudinal connection detail between adjacent girders were then investigated. Figure 2 shows a photograph of a 

transverse flexure test. Observations from 

the girder fabrication and results of the 

structural tests are discussed in detail within 

the corresponding main report.

Conclusions

The design, fabrication, and testing of a 

2nd generation UHPC pi-girder modular 

bridge component has been completed. 

The research program has demonstrated 

the viability of the decked UHPC modular 

girders concept for use in conventional and 

accelerated bridge construction. Girders of 

this type can be fabricated in existing 

prestressed girder production facilities. 

The girder cross section on which the 

research focused is capable of meeting the 

requirements of the AASHTO LRFD Bridge 

Design Specifications with a span length up 

to 87 ft (26.5 m).(5) The transverse flexural 

capacity of the girder is sufficient, and the 

capacity of the longitudinal joint exceeded 

that of the prefabricated deck.

Initial Pi-Girder Deployment

The initial deployment of the UHPC pigirder concept was completed in Buchanan

County, IA. The Jakway Park Bridge opened

to traffic in late 2008. This bridge includes three adjacent 2nd generation UHPC

pi-girders. 

Further Pi-Girder Development

The research completed in this study has 

led to the initiation of a number of related 

studies. A family of pi-girders is under 

development with the intention of developing components for accelerated construction of medium span bridges. Optimal 

connection details between girders and for 

barrier rails are also being investigated. 

Finally, finite element computer modeling 

is being used to better understand the 

structural behavior of UHPC components 

and to facilitate the development of new 

components.

References

1. Graybeal, B.A. (2006). Material 

Property Characterization of Ultra-High 

Figure 2. Transverse flexure test.
4

Researchers—This study was completed by Ben Graybeal of the Federal Highway 

Administration’s (FHWA) Turner-Fairbank Highway Research Center. Additional information 

can be gained by contacting him at 202-493-3122 or in the FHWA Office of Infrastructure 

Research and Development located at 6300 Georgetown Pike, McLean, VA, 22101.

Distribution—The unpublished report (PB2009-115496) covered in this TechBrief is being 

distributed through the National Technical Information Service, www.ntis.gov.

Availability—The report will be available in November 2009, and it can be obtained from 

the National Technical Information Service, www.ntis.gov.

Key Words—Ultra-high performance concrete, UHPC, Fiber-reinforced concrete, Bridges, 

Precast concrete, Prestressed concrete, Bridge design, Accelerated construction, and Durable 

infrastructure systems.

Notice—This document is disseminated under the sponsorship of the U.S. Department of 

Transportation in the interest of information exchange. The U.S. Government assumes no 

liability for the use of the information contained in this document. The U.S. Government does 

not endorse products or manufacturers. Trademarks or manufacturers’ names appear in this 

TechBrief only because they are considered essential to the objective of the document.

Quality Assurance Statement—The Federal Highway Administration provides highquality information to serve Government, industry, and the public in a manner that promotes 

public understanding. Standards and policies are used to ensure and maximize the quality, 

objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues 

and adjusts its programs and processes to ensure continuous quality improvement.

october 2009 FHWA-HRT-09-069

HRDI-06/10-09(100)E

Performance Concrete, FHWA-HRT-06-

103, Federal Highway Administration, 

McLean, VA.

2. Graybeal, B.A. (2006). Structural Behavior 

of Ultra-High Performance Concrete 

Prestressed I-Girders, FHWA-HRT-06-

115, Federal Highway Administration, 

McLean, VA.

3. ASTM. (1997). Standard Test Method for 

Electrical Indication of Concrete’s Ability 

to Resist Chloride Ion Penetration, 

American Society for Testing and 

Materials Standard Practice C1202, 

Philadelphia, PA.

4. Graybeal, B.A. (2009). Structural Behavior 

of a Prototype Ultra-High Performance 

Concrete Pi-Girder, NTIS Report PB2009-

115495, National Technical Information 

Service, Springfield, VA.

5. AASHTO. (2007). AASHTO LRFD Bridge 

Design Specifications, 4th ed., American 

Association of State Highway and 

Transportation Officials, Washington, DC.