The first new H-Pile sizes in decades can provide a more economical way to not only handle heavier design loads for pile foundations, but also save money on column applications, according to piling contractors and structural engineers.
The new sections of HP16 and HP18 — the country’s largest H-Piles ever produced — give engineers and contractors a more economical way to construct deep foundations for buildings and bridges. Another possible benefit of these shapes: using them as columns in building construction.
“HP shapes have webs that are the same thickness as the flanges, in contrast to W-shapes where the web usually is thinner. A thicker web will reduce the need for stiffeners and doublers,” says Charlie Carter, AISC’s vice president and chief structural engineer. “Stiffeners cost hundreds of dollars each and a typical doubler plate might cost a thousand dollars. Total these numbers per moment-connected column and that’ll add up quickly. Plus, the HP section weight might be less than the W-shape weight required to eliminate the stiffeners and doublers.”
The ASTM standard specification for structural shapes and piling products now includes a total of 10 new HP16 and HP18 profile sections and footweights. Six are within the HP16 range, varying from 88 to 183 pounds per foot in 20-pound increments; and four are within the HP18 range, varying from 135 to 204 pounds per foot with about the same increments. Until now, the industry has only relied on four nominal sizes of H-Piles: HP8, HP10, HP12, and HP14.
These larger sizes can save as much as 30 percent on both labor costs and time to drive the piles, says Michael Wysockey, president of Thatcher Foundations, a leading piling contractor that hosted a test for the new H-Piles – driving a 150-foot long HP16x141 to bedrock to demonstrate its usefulness as a foundation component.
“As you get into larger structures, taller buildings, heavier loads, where a column would have a 15-pile cluster, now it might take only 10,” Wysockey says. “They drive great, too. You can put big hammers to them and they hold up really well. You can drive through hard clay and dense silts and get to rock so you get to use the majority of the available strength of the steel.”
Saving on material, labor
The new H-pile sizes should help save a total of almost $20,000 in material and labor on a sewer project in Hawaii, says Tim Pearia, an engineer with Frank Coluccio Construction.
According to Pearia, the job will require bigger shafts for two reasons: First, it’s a gravity line, not a pump station, so it needs to be deeper. And second, the sewer line will have a 72-inch diameter — twice the size of a typical project. Until now, this type of project would have likely required wide-flange, 14-inch sections that needed to be doubled up in some parts. Because of the new HP 16 x 183 sections, though, Pearia says crews will need one or two fewer frames for each of the five shafts — reducing the total amount of beam needed by about 500 feet.
That should save as much as $8,000 in material, Pearia says. And it also will save about $10,000 in labor, because each frame will now require fewer man days per frame.
The first of the 15 H-Piles were installed in September, and the project should be finished in 2012.
“For years, that 14-inch H-pile section was the biggest thing you could get, so it’s nice to have another size,” Pearia says. “And the guys really like that heavier web. It’s just a sturdier cross-section all around.”
The new sizes should save about $12,000 in material on a wind tower project in Bayonne, N.J., says Richard Betron, vice president of MG Forge Construction. Normally, the three foundations needed for the wind towers would require W14 x 193 sections. By instead using HP 18 x 181 sections, it should reduce the amount of material needed by about 11 tons.
Modernizing the H-Pile industry
Unlike smaller sizes, the new sections of HP16 and HP18 — produced by Nucor-Yamato Steel Company — can carry more load while also meeting building codes that call for compact sections, according to Ashraf Elsayed of Hall, Blake & Associates – A Division of Geotechnology, Inc., a geotechnical, environmental engineering and materials testing firm. Elsayed helped with the load test of the new H-Piles.
The new, larger sizes also have significantly smaller top settlements at comparable loads, reducing the amount of downward deflection, according to industry observers. And they show significant improvement in end bearing, skin friction and lateral-resistance capacity.
“When engineers see this, they will instantly see the benefits,” says Reidar Bjorhovde, a 45-year veteran who headed the civil engineering department at the University of Pittsburgh and now runs a consulting firm. “These new sections will be capable of carrying larger loads, whether it’s for a high-rise or an industrial structure. Right now, engineers have to combine smaller shapes, using more of them and placing them closer together. The fact that you can use fewer piles will reduce cost.”
Michael F. Engestrom is the technical marketing director at Nucor-Yamato Steel. He can be reached at MEngestrom@nucor-yamato.com.