Two Enerpac hydraulic cylinders pull on the strands and mimic the pressure they would undergo outside of the lab at the University of Nebraska-Lincoln Durham School of Architectural Engineering and Construction.
(Photos courtesy of Enerpac)
Three years ago, when Marc Maguire, assistant professor of construction programs at the University of Nebraska-Lincoln (UNL), started investigating a new stranded wire product for bridge girder reinforcing, he thought the best strands for bridge construction were the industry standard 7-wire strands.
After running a multitude of analyses, Maguire and student researchers found that 19-wire 1-1/8 in. diameter strands outperform the typical 7-wire 1-1/6 in. diameter strands and allow bridges to reach unprecedented lengths. Further tests conducted by the Durham School of Architectural Engineering and Construction, with the help of Enerpac hydraulic tools, examined the bond strength, force transfer and development length of the 19-wire strands.
"Traditionally, 19-wire strands are not often used in the United States because they are not widely available and they are much larger than standard strands," said Maguire. "We wanted to show that there was an alternative option to the common 7-wire strand — one that can perform at the same level, if not better."
Results from Maguire's tests are not only impressive, they are highly impactful for several reasons. First, the bond of the concrete to the strand seems to be higher for 19-wire strands, which allows surprisingly efficient force transfer. Using a 19-wire strand also could reduce fabrication costs as less strands will be used in comparison to the 7-strand method.
Finally, the strands can reach longer spans, up to 10 percent longer than conventionally reinforced bridge girders, which reduces construction costs in some situations because intermediate piers may be avoided. Further, when making long span concrete girders, there are limited options for pushing total span length beyond what has already been done, and these 19-wire strands may be a viable strategy.
Enerpac Hydraulic Cylinder Helps Apply Force to Test New Strands
To test the strength and durability of the 19-wire strands, researchers used a variety of different tests including: The large block pullout test (LBPT), ASTM 1081 standard test, concentrically reinforced untensioned prisms (CRUP), large-scale tests, effective prestress and flexural test and material testing.
"For fabricating our specimens, it is very difficult to generate enough force to safely pull on the 19-wire strands. Conventional strands have specialized equipment for doing this that does not exist for these strands," said Maguire. "That's where Enerpac came in and provided the tools to make these experiments happen."
To help pull on the strands, the test used the Enerpac RR20013 double-acting, general purpose hydraulic cylinder with a 221-ton capacity and 13.00 in stroke that the university has been using for years to conduct tests. The linear motion and high force produced by the cylinder gave the researchers what they needed to replicate the stress that these strands will be undergoing if used in a bridge girder.
To prevent accidental over-pressurization, the hydraulic cylinder features a built-in safety valve. The researchers also used Enerpac hand pumps to apply hydraulic pressure with even more accurate control and simplicity as needed.
"The Enerpac equipment's simplicity and reliability is why we've relied on it for decades to conduct tests and fabricate our own prestressed concrete specimens. In addition, the reliable service is extremely helpful to the university. The territory manager will visit the lab regularly to conduct inspections, make equipment recommendations and train new students," said Maguire. "And for a test like the wire strand testing, easy-to-use equipment with dependable expertise is paramount."
The precision and combination of the Enerpac equipment allowed Maguire and his team to simulate stressors, producing accurate and consistent results.
Results Show Promising Future for 19-Wire Strands
The results presented in a formal written report found that bridge designs with medium- to higher-strength concretes could be using 19-wire 1-1/8 in. diameter strands as the number of strands needed is dramatically reduced, the maximum span achievable is greater and they are safe to undergo expected loading.
"Three years ago, we didn't know a new $1 trillion infrastructure bill would be passed and a lot of bridges would be getting updates that they so desperately need," said Maguire. "We hope that this research can show that 19-wire 1-1/8 in. strands can be a tool in the tool belt."
Testing hasn't formally concluded, but Maguire is confident that the 19-wire strand meets engineering expectations and is a viable option for long-span concrete girder applications.
For more information, visit enerpac.com.
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