TECHBRIEF Structural Behavior of a

Prototype UHPC Pi-Girder 

FHWA Publication No. of this TechBrief: FHWA-HRT-09-068 

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This document is a technical summary of the unpublished 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 Prototype 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: 

PB2009-115495

Objective

This TechBrief highlights the results of a research program 

that evaluated an ultra-high performance concrete (UHPC) 

pi-girder cross section prototype developed for use in shortand medium-span highway bridge applications.

Introduction

UHPC is an advanced cementitious composite material which 

has been developed in recent decades. When compared to 

more conventional concrete materials, UHPC tends to exhibit 

superior properties such as exceptional durability, high 

compressive strength, usable tensile strength, and longterm 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. Structural testing was completed on 

girders to investigate their flexural response, shear response, transverse flexural response, and lateral load distribution capabilities. Through this work, topics related to the 

design and 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 materials, namely UHPC. As a class, these concretes tend to contain

Research, Development, and 

Technology

Turner-Fairbank Highway 

Research Center

6300 Georgetown Pike

McLean, VA 22101-2296

www.tfhrc.gov
2

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)

UHPC Prototype 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. Topics such as creating longer lasting 

bridges through enhanced durability or 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.

The development of a decked girder prototype member which utilized UHPC as the 

primary structural component was initiated 

during the early stages of the Federal Highway Administration’s (FHWA) UHPC research 

program. It is evident that UHPC’s mechanical 

and durability properties allow for beneficial modifications to conventional concrete 

bridge component solutions. It also allows 

for the development of previously impractical 

components. Given the prior applications of 

conventional concrete decked girder members 

in infrastructure applications and the construction of the Peace Footbridge in Seoul, 

South Korea, a decked pretensioned girder 

with slender cross sectional dimensions was 

envisioned as a prototype solution.

The cross section dimensions of the UHPC 

pi-girder prototype were established through 

an analytical study completed at the 

Massachusetts Institute of Technology.(4,5) The 

models implemented in the design included 

one-, two-, and three-dimensional analyses

of the predicted response of the girder to 

the loadings prescribed in the AASHTO LRFD 

Bridge Design Specifications.

(6)

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. UHPC pi-girder cross section prototype.

6.1 inches

(156 mm)

96 inches

(2,430 mm)

3.3 inches (84 mm)

3 inches

(76 mm)

55 inches

(1,390 mm) 33 inches

(840 mm)
3

The girder prototype is a modular component designed to span 70 and 100 ft (21

and 30 m). Figure 1 shows a UHPC pi-girder

cross section prototype, which is 96 inches

(2.4 m) transversely and 33 inches (0.84 m)

deep. It can also be prestressed by up to

15 strands in each bulb.

Test Program

This research program included two phases. 

The first phase focused on the fabrication of 

four UHPC pi-girders. These 70-ft (21.3-m)-

long prestressed girders were fabricated at a 

conventional precast bridge girder production 

plant and then transported to FHWA’s TurnerFairbank Highway Research Center (TFHRC). 

The second phase of the research focused 

on the physical testing of these full-scale 

girders through the application of structural 

loads. Three tests including primary flexure 

and shear, transverse flexure, and load distribution were conducted. Figure 2 shows a 

full-scale shear test of the pi-girder prototype underway in the laboratory. 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 UHPC 

pi-girder prototype demonstrated that the 

concept of decked UHPC modular girders for 

bridge construction is viable. Girders of this 

type can be fabricated in existing prestressed 

girder production facilities. The structural response of the girder prototype exceeds design requirements in terms of ultimate shear

capacity and meets flexural design requirements with the inclusion of appropriate 

prestress force. The load distribution capability of the girder is limited, so distribution 

of live loads beyond adjacent girder legs is 

not recommended. The transverse flexural 

capacity of the girder is insufficient to elastically resist service-level wheel loads.

Further Pi-Girder Development

The research results presented in the corresponding report have led to the further development of the pi-girder concept. A 2nd generation pi-girder has been designed, full-scale 

test girders have been fabricated, and testing has begun. The 2nd generation pi-girder 

retains the initial concept, but it has been 

modified to provide significantly increased 

transverse flexural capacity while also allowing for simplified fabrication. Results of this 

follow-up program will be published in the 

near future.

References

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

Characterization of Ultra-High 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.

Figure 2. Full-scale shear test.
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Researchers—This study was completed by Ben Graybeal of Federal Highway Administration’s (FHWA) Turner-Fairbank Highway Research Center. Additional information can be 

found 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 (PB2009-115495) 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-09-068

HRDI-06/10-09(100)E

4. Park, H. (2003). Model-Based Optimization 

of Ultra-High Performance Concrete Highway Bridge Girders, 139, Massachusetts 

Institute of Technology, Cambridge, MA.

5. Soh, M. (2003). Model-Based Design of a 

Ultra-High Performance Concrete Prototype Highway Bridge Girder, 64, 

Massachusetts Institute of Technology, 

Cambridge, MA.

6. AASHTO. (2002). AASHTO LRFD Bridge 

Design Specifications, 2nd ed., American 

Association of State Highway and 

Transportation Officials, Washington, DC.