OAKLAND -- Early results from the unprecedented bolt testing on the new Bay Bridge span are reassuring engineers and officials.
So far, tests on hundreds of Bay Bridge bolts made out of an identical grade steel as the anchor rods that snapped in March show no signs of failure, according to a top project engineer.
"Everything is looking pretty good at this point," said Mazen Wahbeh, a consulting materials engineer leading the bolt-testing regimen for the three agencies overseeing construction of the new eastern span. "We haven't seen any evidence of embrittlement."
The preliminary results are a bit of welcome news on a project beset with delays, cost overruns and wavering public confidence dating back to 1997, when then-Gov. Pete Wilson ordered the seismically vulnerable span replaced rather than retrofitted.
The $6.4 billion span is California's most expensive public works project to date.
It may also be the most tested.
Metallurgists blame hydrogen embrittlement for the failure of 32 of 96 very large -- 3 inches in diameter and 17 to 23 feet long -- steel bolts embedded in seismic stabilizers on the pier east of the tower.
It is a phenomenon found in high-strength galvanized steel under heavy strain, where hydrogen atoms squeeze into the spaces between its latticed molecules, and leave the bolts brittle and vulnerable to fracture.
To learn if the span's other 2,210 fasteners are susceptible to imminent fracture, the Bay Bridge team is subjecting every bolt they can get their hands on to least one test. Samples and full-sized rods of nearly every type will undergo up to a dozen more types of tests.
Results will be logged and analyzed in the coming days as the engineers from the three agencies overseeing the bridge construction -- Caltrans, the Bay Area Toll Authority and the California Transportation Commission -- prepare their findings for a public briefing set for July 10.
A good outcome from the bolt testing means none of the fasteners requires immediate replacement and it becomes one less reason to postpone the planned Sept. 3 opening.
A bad outcome means one or more types of bolt shows evidence of unacceptable weakness and replacements must be ordered, fabricated and installed before traffic is permitted on the span.
Between the best- and worse-case scenarios, engineers will recommend reducing the loads to decrease the strain or adding dehumidifiers that reduce levels of corrosive marine moisture.
"No final decisions have been made yet," Wahbeh said. "We're waiting for all the results to come in."
The agencies are also waiting to hear if American Bridge/Fluor Enterprises, the bridge contractor, will finish retrofitting the shear keys where the bolts broke in time to open the bridge as scheduled.
Engineers won't hold off opening the bridge for the outcome of planned long-term testing that will measure whether the marine environment will degrade the bolts and over what time period. The 11 test beds are under construction and the results are months away.
To help craft the bolt autopsy spurred by March's catastrophic failure, the bridge team hired some of the top names in corrosion -- University of Texas at Austin engineering professor Karl Frank, Newport Beach engineering consultant Louis Raymond and embrittlement test pioneer Herb Townsend.
The testing plan includes:
The list includes a very large 4-inch diameter anchor rod, one of 424 bolts that keep the tower aligned with the foundation during an earthquake.
But more analysis may be required.
Caltrans hasn't yet located the results of the state's tests of the bolts, which were conducted in 2007 before installation.
Documents that were found indicate Houston Galvanizing Services in Texas violated the project specifications and immersed the bolts in an acid bath -- called pickling -- before dipping them in molten zinc. Caltrans ordered the bolts sandblasted rather than pickled, a safeguard against embrittlement established by ASTM International, formerly known as the American Society of Testing and Materials.
Caltrans inspectors also ordered tower bolt contractor, Kiewit Offshore Services, to stop applying zinc from aerosol spray cans. The practice is prohibited and the company had to strip the sprayed zinc off the rods.
However, bridge engineers say the tower bolts have shown no signs of embrittlement and they are tightened to 25 percent of their capacity, well below the 50 percent threshold metallurgists say increases susceptibility to cracking. The Bay Bridge design team originally relied on materials and testing standards for hot-dip galvanized high-strength steel fasteners established by ASTM.
Developed by industry experts, the standards specify how the steel is made and its mechanical properties. The guidelines also spell out testing methods.
Caltrans, steel mills, fabricators and contractors conducted more than a dozen required tests on every type of fastener used on the Bay Bridge.
Most met the standards and the few that didn't were rejected, according to 17 volumes of bolt test data released by Caltrans.
The manufacturers and Caltrans appear to have largely stuck with minimum ASTM testing guidelines with several exceptions.
In late 2008, Caltrans added an extra test -- magnetic particle -- that measures surface anomalies. ASTM doesn't require it, but engineers were worried the thread-cutting equipment would initiate surface cracks on the rods.
But neither the state nor the contractors tested all the bolts for hydrogen embrittlement, as ASTM recommends.
Using a full-sized rod, the tests range from applying a single sharp hammer blow to bending to placing it under load for 48 hours and examining it under a microscope for cracks.
Most of the fasteners were too large for the available testing equipment, Wahbeh said. All but 96 of the 2,306 bolts range in size from 2 to 4 inches in diameter and reach up to 32 feet long.
"The ASTM tests were designed for smaller bolts with a diameter of 1¿1/2 inches or less," he said. "It would take an incredibly large piece of testing equipment to bend these large bolts or apply the loads required, and they aren't widely available."
In any case, these embrittlement tests are useless today, said University of Pennsylvania materials engineering Professor Emeritus Charles McMahon.
"This would be a test to determine whether the specimens had internal hydrogen, resulting from previous processing or storage conditions, " he said. "It has nothing to do with service conditions in a marine environment."
The high-strength steel bolts on the Bay Bridge are being subjected to an unprecedented testing regimen following a catastrophic failure of anchor rods last spring. The bridge construction team will redo many of the tests performed on the products during fabrication, but they have added several new ones. Here's a sample:
Chemistry -- A spectrometer measures elements in steel such as carbon, manganese, phosphorus, sulfur, silicon and aluminum.
Hardness -- A hard-tipped indenter is pressed into a steel sample. The amount it displaces is measured and the results are reported on a relative scale. On the Rockwell scale, the higher the number, the harder the steel.
Strength -- Force is applied to a sample. Measured in pounds, the point at which it begins to deform is its yield and where it breaks is its ultimate tensile strength. The more force required, the stronger the bolt.
Ductility or flexibility -- A sample is stretched until it breaks. Elongation measures how much it stretches as a percentage of its original size. The higher the percentage, the greater the flexibility.
Magnetic particle -- With an electrical current running through the bolt, technicians apply a metallic spray and examine the part for metal concentrations that indicate the presence of surface cracks.
Acoustic emission sensors -- Instruments placed on the rods record the energy produced when a crack initiates, spreads or moves.
Toughness or Charpy v-notch -- A small rectangular sample from the rod is notched and struck with a sharp point affixed at the end of a swinging pendulum. Measured in foot pounds, the results show the metal's resistance to the spread of cracks.
Microscope -- A cross-section slice is magnified 1,000 times and its microstructure examined for evidence of cracking.
Long-term stress corrosion or Townsend tests -- Incremental force is applied over time to a full-size bolt in which its threads are submerged in a sealed saltwater solution. Measured in pounds of force, the results show its resistance to embrittlement in a marine environment. The other test calls for placing under load a smaller rod section in a saltwater solution and measuring the rate at which the cracks spread. The results show the rate of failure.
Source: Bay Bridge materials engineer Mazen Wahbeh