OAKLAND -- Problems with finding the cause and a fix for broken bolts on the new Bay Bridge might delay the span's promised Labor Day grand opening, transportation officials said Wednesday.
Engineers are considering several options for making the new span seismically safe, including installing steel collars and a concrete cap design, along with the replacement of the steel rods with another type of material. They suspect the broken rods suffered hydrogen contamination but admitted they may never know the cause.
Until investigators determine the precise reason for the failure and a solution, the opening timetable is "guesswork," Metropolitan Transportation Commission Chairman Steve Heminger told the commission's toll bridge oversight committee during a briefing.
"As you know, this bridge would have opened several years ago if we hadn't had the political delays. This is one of the first real construction problems we've had."
On the other hand, the construction team later told media members that the bridge could open to traffic before the repair if the experts determine the new span is safer than the existing cantilever, which sits on wooden pilings sunk into the mud. Engineers have declared the old bridge highly vulnerable during the next earthquake.
"We will be actively pursuing that analysis, but it has not been done yet," said Andrew Fremier, who leads the commission's toll bridge division.
Despite the unknowns, the construction team on Wednesday did identify hydrogen contamination rather than installation or design problems as the likely culprit that caused the fracture of 32 high-strength steel anchor rods placed in two shear keys atop the large pier just east of the tower.
The keys are sandwiched between the pier and the bridge deck and help control sideways movement during an earthquake. The bolts clamp the three pieces together.
Microscopic tests performed on one of the broken rods at 1,000 magnification show the presence of hydrogen, which works its way into the spaces between the steel grains and weakens the bolts. All 32 rods, varying in size from 9 feet to 24 feet long, 3 inches in diameter and embedded in concrete, broke at the first thread in the bottom of the shear key.
Bridge team leaders say they don't know where hydrogen infiltrated the rods and may never know.
It could have infected the steel in the manufacturing process or after installation while the rods were exposed to the weather, they said.
Inspectors found water in the bottom of the steel casings that held the rods, which could have triggered corrosion and exposed them to hydrogen despite a zinc coating designed to keep water out.
"No one thought the water was going to be a problem," said Stephen Maller, deputy director of the California Transportation Commission. "If we knew where we were going to fall, we would have put down a pillow."
State Sen. Mark DeSaulnier said in a statement that public safety has to be the priority.
"The new Bay Bridge is the largest public works project in state history, and Caltrans owes it to the commuters to deliver a safe bridge," Senator Mark DeSaulnier (D-Concord) said. "Caltrans needs to take the time necessary, and not cut corners, to get the bolt problem fixed."
Dyson Corp., based in Painesville, Ohio, along with a number of subcontractors, in 2008 fabricated the 32 failed bolts along with the other 64 installed in the two problematic shear keys.
Two years later, the same company manufactured a second batch of 192 bolts that crews installed in adjacent shear keys and bearings.
Crews tightened those bolts starting March 31, but none have failed, Caltrans Toll Bridge Program Manager Tony Anziano said. Inspectors have installed monitoring equipment that sends electromagnetic signals into the rods and detects wavelength changes that could indicate cracking.
Anziano and the bridge team reassured the commission and the public, saying that none of the remaining 250,000 metric tons of permanent steel on the bridge is likely to crack.
Inspectors examined the other 2,000 high-strength Dyson-produced steel parts found elsewhere on the bridge, including the cable saddle, and found no problems, Anziano said.
None of the other high-strength galvanized bolts are subject to the same intense loads as those in the shear keys and bearings, and embrittlement tends to happen within days or weeks, not months or years, he added.
Bridge team leaders concede that the numerous quality control or assurance tests failed to detect the problem, which cleared the way for crews to install the specialty bolts into a space where they could not be replaced. There's only five feet of clearance between the top of the bolt and the bottom of the bridge deck, and the rods are too long to pull out in one piece.
Of the 150 results in tests conducted by the manufacturer and Caltrans on the 2008 bolts, five performed by the state failed to meet the requirements set by ASTM International, formerly the American Society of Testing and Materials.
All five involved elongation, which measures how much the steel stretches as a percentage of its original size. The standard requires no less than 14 percent elongation and the suspect test samples showed rates of 12.5 percent to 13.6 percent. Caltrans engineers reviewed the anomalies and, given the overall results, they approved the rods for use, Anziano told the commission.
The elongation deviation does not indicate a hydrogen problem; in fact, one of the broken rods recently passed all of the industry standards, he later said.
Hydrogen embrittlement is a well-known industry problem dating back to the late 1800s.
While steel manufacturers have devised numerous coatings and processes designed to minimize the contamination, the problem persists in everything from battleships to airplanes to nuclear plants.
In February, two oil drillers on the Gulf Coast began replacing 9-inch-long, 2-inch-diameter bolts on as many as 24 rigs after General Electric & Gas found possible hydrogen contamination, according to Oilgram News.
Chosen for its combination of strength and flexibility, or ductility, high-strength steel is tested to make sure it meets chemical and mechanical properties set by ASTM International, formerly known as the American Society for Testing and Materials. Among the tests metallurgists use:
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, one of the options is the higher the number, the harder the steel.
Elongation and reduction of area: A sample is stretched until it breaks. Elongation measures how much the steel stretches as a percentage of its original size. Reduction of area measures the amount of deformation in a cross-section of the sample. Both measures indicate the steel's ductility.
Tensile strength: A sample is stretched until it breaks. The point at which it snaps is measured as pounds of force.
Yield strength: Force is applied to a sample. The results show how many pounds of force it can withstand before it yields or gives way.
Proof load: A specified load is applied to the rod to see whether it permanently deforms or stretches.
Sources: ASTM International and Testing Engineers of San Leandro