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Crosstown hammer testing unresolved
Hydraulic hammer trials show the elevated road can handle normal stress. Opinions vary on if that's enough.
By JEAN HELLER
Published January 21, 2005
TAMPA - The Mother of All Pile Hammers gave the support columns of the Lee Roy Selmon Crosstown Expressway its best shot, and they stayed put.
Some engineers, though, say they're still not safe enough.
Twelve support structures under the elevated lanes of the Crosstown that were pounded by the world's largest hydraulic hammer didn't move under stress far exceeding anything the columns would bear in actual use, test results show.
But engineering consultants hired by the Tampa-Hillsborough Expressway Authority say new, tougher safety standards should be applied to those results. Under those standards, 10 of the 12 columns on the 6-mile, three-lane toll road don't measure up.
Two reports released Thursday by opposing interests in the elevated roadway give vastly different pictures of repairs required before the $350-million project can open to traffic.
URS, the original general engineering consultant , said in its report on the hammer testing that under the heaviest pounding, none of the 12 subterranean support structures moved more than .2 of an inch. The allowable settling during construction was 1 inch.
The second report came from Ardaman & Associates, a soils consultant hired by the Expressway Authority to determine the composition of the ground under the bridge and what needs to be done to make the structure safe. It said the bridge requires a greater margin of safety than the standard used during initial construction.
The reports' bottom lines are vastly different in terms of how much work will be necessary to fix the bridge and how much it will cost. They signal further legal action ahead, although Ralph Mervine, interim executive director of the Expressway Authority, said the parties were going to seek mediation instead of litigation.
"We would all prefer that because the issues are so highly technical and involved," Mervine said.
That does not mean the parties are any less at odds, however.
"We have a definite difference of opinion," said Tom Logan, regional vice president for URS.
In a related development, the DOT is making changes statewide in certain design, construction and inspection requirements for bridge supports like those under the Crosstown.
The new standards, outlined in a memorandum written last month by DOT's structures design engineer William Nickas, say the changes apply to all future projects, as well as to those now under design.
The requirements call for additional soils testing, additional inspection of the shafts drilled for the support columns and additional checks on the integrity of the concrete in the columns.
"This memorializes FDOT policy," Nickas said in an interview Thursday. All single, drilled shafts need to have additional inspections, he said.
Asked if the experience with the Crosstown - which is not a DOT project - prompted his Dec. 13 memo, Nickas replied:
"If I said the experience and knowledge of what happened at the Crosstown was ignored when the memo was issued, I'd be lying."
At issue with the Crosstown is the ability of each support column to resist the stress of the combined weight of the bridge itself, lights and signs and peak traffic.
Once it's determined what a shaft can take, engineers lower, or "discount," that number to build in an extra safety factor. Then they build more resistance into the shaft to cover that hedge, said Joe Amon, vice president of Ardaman.
The standard "discount" for the type of shaft under the Crosstown is 20 percent, and that is the standard URS officials say they used. After studying the soils under the supports, Ardaman determined that it should discount the columns' capacity for stress by 35 percent. Only two of the 12 columns tested met that standard, though a third came very close.
The Ardaman report does contain some good news, however. It decreases very slightly the total number of columns that need additional support and decreases significantly the number that need the most expensive type of repair.
In a preliminary document released in November, Ardaman estimated that of the 218 total support columns, 105 would need heavy concrete bracing, or "sister shafts." They cost about $425,000 when built next to shafts that already have roadway on top and about $215,000 for supports without roadway.
The new report nearly halves the number of columns needing sister shafts to 56.
The number of shafts needing less expensive fixes rises from the 60 estimated in November to 99 estimated now. And the number of shafts that need no work goes from an estimated 53 to 63.
The less expensive work would cost between $7,500 and $125,000 per shaft.
URS estimates the number of shafts that need repair at fewer than 20.
The Expressway Authority originally estimated that the cost of repairs would be as high as $80-million, with $40-million for new construction.
Mervine said Thursday that Ardaman's new repair schedule could reduce the construction costs by $5-million.
Work on the bridge is expected to resume in March with an opening scheduled for mid-2006, a year behind schedule. The bridge will carry three lanes of traffic from Brandon to Tampa in the morning and will reverse to carry outbound traffic at night. It will be for the exclusive use of subscribers to SunPass, the automated toll system.
[Last modified January 21, 2005, 00:29:18]
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