TECHBRIEF

Research, Development, 

and Technology

Turner-Fairbank Highway 

Research Center

6300 Georgetown Pike

McLean, VA 22101-2296

www.fhwa.dot.gov/research

Splice Length of Prestressing 

Strand in Field-Cast 

Ultra-High Performance 

Concrete Connections

FHWA Publication No.: FHWA-HRT-14-041

FHWA Contact: Ben Graybeal, HRDI-40, (202) 493-3122, 

benjamin.graybeal@dot.gov.

This document is a technical summary of the Federal 

Highway Administration report, Splice Length of Prestressing 

Strands in Field-Cast UHPC Connections (FHWA-HRT-14-047), 

available through the National Technical Information Service at 

www.ntis.gov.(1)

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

PB2014-103454.

Objective

The objective of this research was to determine the lap splice 

length of untensioned prestressing strand in field-cast ultrahigh performance concrete (UHPC). 

Introduction

The development length of reinforcements embedded into 

UHPC can be significantly shorter than the lengths normally 

associated with conventional concrete. Shortening the development length of prestressing strand can allow for a redesign 

of some structural systems, including spliced girder and 

continuous-for-live-load bridges. UHPC, when used in field-cast 

connections between prefabricated bridge elements, can create 

robust connections that emulate monolithic components. 

UHPC is a cementitious composite material composed of an optimized gradation of granular constituents, a water-to-cementitious 

materials ratio less than 0.25, and a high percentage of discontinuous internal fiber reinforcement. The mechanical properties 

of UHPC include a compressive strength greater than 21.7 ksi 

(150 MPa) and sustained post-cracking tensile strength greater 

than 0.72 ksi (5 MPa). UHPC has a discontinuous pore structure 

that reduces liquid ingress, significantly enhancing durability 

compared with conventional concrete.(1,2,3)

Connecting adjacent pretensioned elements to one another 

affords the opportunity to increase the efficiency of the structural design, accelerate the construction, and enhance the 
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serviceability of the structure. Connections engaging prestressing strands extending from the components are rarely designed or implemented due 

to the need for expensive mechanical connectors 

or long lengths of strand (and thus geometrically 

large connections). Critical connections in which 

splicing of existing strands might have been 

appropriate have traditionally been completed 

using either post-tensioning systems or supplemental mild steel reinforcement.

UHPC-class materials have been demonstrated to 

significantly decrease the development length of 

embedded reinforcing elements. As such, UHPC 

may afford a new opportunity to reconsider the 

traditional methods for connecting prestressed 

elements, including the splicing of prestressing 

strands. It may be possible to reduce the embedment length of prestressing strands to the point 

that splicing of pretensioned elements becomes 

a viable design concept and construction technique. Most notably, this concept could advance 

the state-of-the-practice for multispan continuous structures and for spliced girder structures.

Test Program

This study investigated the development length 

of 0.5- and 0.6-inch (12.7- and 15.2-mm) diameter 

untensioned prestressing strands embedded in 

steel fiber and polyvinyl alcohol (PVA) fiber reinforced UHPC. The volumetric fiber content was 

2 percent. The compressive strength of the steel 

fiber reinforced UHPC at the time of strand splice 

testing was approximately 23.5 ksi (162 MPa). 

As is common when reduced stiffness fibers 

are used in UHPC, the compressive strength of 

the PVA fiber reinforced UHPC was reduced to a 

value of approximately 19.5 ksi (134 MPa).

A development length test was designed that 

allowed for the replication of the tension—

tension stress state that could occur when 

two strands were lap spliced within a connection between two linear elements. The specimen geometry and test setup are shown in 

figure 1. The non-contact lap lengths tested 

ranged from 8 to 24 inches (20.3 to 61.0 cm) for the 

0.5- and 0.6-inch (12.7- and 15.2-mm) diameter 

prestressing strands embedded in steel fiber 

reinforced UHPC. The non-contact lap lengths 

ranged from 8 to 36 inches (20.3 to 91.4 cm) 

for the 0.5-inch (12.7-mm) diameter prestressing strands embedded in the PVA fiber reinforced UHPC. Specimens were cast and cured 

in an ambient laboratory environment. Figure 2 

shows the casting of 1 of the 18 test specimens.

The tests were completed under displacement 

control in a servo-hydraulic testing machine as 

shown in figure 3. The load resisted by the specimen and the slippage of the dead end of the single prestressing strand were captured throughout each test. Tests were continued until well 

after the peak resistance was achieved or until 

the strand ruptured. Each test was completed 

between 28 and 32 days after casting of the UHPC.

Figure 2. Casting of a 20-inch (50.8-cm) long test 

specimen.

Figure 1. Test specimen geometry and loading setup.
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Test Results

The implemented test method proved capable 

of demonstrating the different behaviors that 

could be exhibited by unstressed prestressing 

strands embedded into field-cast UHPC. Longer 

embedment lengths correlated with higher 

strand stresses at peak resistance. Figure 4 

provides the test results with the nominal strand 

strength of 270 ksi (1,860 MPa) shown as a dotted 

line. The three types of specimens are shown 

with the range of embedment lengths tested.

The behavior of each specimen can be described 

as follows. Initially, the response appeared 

elastic, with the single strand effectively transferring all applied load through the UHPC into 

the lapped strands. If the lap length was long 

enough, transverse tensile cracks appeared 

in the UHPC. Next, most specimens began to 

exhibit splitting cracks that began at the loaded 

end of the single strand and ran along the length 

of the specimen. In nearly all cases, this crack 

eventually extended along the entire length of 

the specimen, resulting in a loss of confinement 

of the strand and a reduced resistance to continued loading. In two cases with the 0.5-inch 

(12.7-mm) diameter strand and longer embedment lengths in the steel fiber reinforced UHPC, 

the prestressing strands ruptured prior to the 

generation of a full-length splitting crack.

Visual observations during and after the tests 

indicate that the steel fiber-reinforced UHPC 

specimens exhibited tighter cracks, in particular, the splitting crack that tended to run the 

length of the specimen immediately prior to 

the attainment of peak resistance. Cracks in 

the PVA fiber reinforced specimens were wider. 

This is likely due to the lower elastic modulus of the PVA fibers, resulting in a reduced 

crack opening stiffness. The PVA specimens 

would then generate less clamping force on the 

strands and thus, as observed, would require 

a long embedment length to fully develop 

the strand.

Figure 3. Test specimen in load frame.

Figure 4. Peak strand stress versus lap splice length.

1 inch = 0.0254 m

1 ksi = 6.895 MPa
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Researchers—This study was conducted by Ben Graybeal at FHWA’s Turner-Fairbank Highway 

Research Center. For additional information, contact Ben Graybeal at (202) 493-3122 or in the FHWA 

Office of Infrastructure Research and Development located at 6300 Georgetown Pike, McLean, VA, 

22101-2296.

Distribution—The report (PB2014-103454) covered in this TechBrief is being distributed through the 

National Technical Information Service at www.ntis.gov.

Availability—This TechBrief may be obtained from the FHWA Product Distribution Center by email to 

report.center@dot.gov, fax to (814) 239-2156, phone to (814) 239-1160, or online at http://www.fhwa.dot.

gov/research.

Key Words—Ultra-high performance concrete, UHPC, fiber-reinforced concrete, prestressing strand, 

development length, bond stress.

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 high-quality 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.

FEBRUARY 2014 FHWA-HRT-14-041

HRDI-40/02-14(250)E

Conclusion

The objective of this research was to determine 

the lap splice length of untensioned prestressing 

strand in field-cast UHPC. The results suggest 

that, for the steel fiber reinforced UHPC, the 

0.5-inch (12.7-mm) diameter strands can be fully 

developed within 20 inches (0.51 m), and the 

0.6-inch (15.2-mm) diameter strands can be fully 

developed in approximately 24 inches (0.61 m). 

The 0.5-inch (12.7-mm) diameter strands can 

be fully developed in the PVA fiber reinforced 

UHPC in approximately 36 inches (0.91 m). In 

all cases, greater or lesser confinement of the 

strands would result in changes in the development length. Confinement parameters of interest include cover; fiber reinforcement type, 

volume, and efficiency; passive transverse 

reinforcement; and concrete tensile response.

References

1. Graybeal, B., (2011). Ultra-High Performance 

Concrete, Report No. FHWA-HRT-11-038, 

Federal Highway Administration, Department 

of Transportation, McLean, VA.

2. Graybeal, B., (2012). Construction of FieldCast Ultra-High Performance Concrete 

Connections, Report No. FHWA-HRT-12-038, 

Federal Highway Administration, Department 

of Transportation, McLean, VA.

3. Russell, H., and Graybeal, B. (2013). UltraHigh Performance Concrete: A State-ofthe-Art Report for the Bridge Community, 

Report No. FHWA-HRT-13-060, Federal 

Highway Administration, Department of 

Transportation, McLean, VA.