Last year, Bay Area motorists could glance up at huge billboards complaining, “Bay Bridge: 100% Foreign Steel” — part of a campaign launched by domestic manufacturers and union groups.

The messages were intended to shame Caltrans and the Metropolitan Transportation Commission, the state agencies that own and operate the structure, for purchasing steel from China for the bridge’s new self-anchored suspension span.

Then this month, inspectors discovered that more than 30 stabilizing steel rods in the self-anchored span had cracked, prompting early fears that they were the result of shoddy material from a distant country. But the steel was produced domestically by a manufacturing firm in Ohio called Dyson Corp.

American firms comprise 76 percent of the total contracts of the Bay Bridge’s eastern span rebuild project, but that figure includes everything from temporary scaffolding structures to small rebar strands, according to John Goodwin, spokesman for the Metropolitan Transportation Commission.

For the self-anchored suspension span — the soaring centerpiece of the bridge’s eastern section — the majority of the steel came from China. The broken rods from Ohio — which bolt the roadway to the towers rising out of the water for seismic stabilization purposes — are part of a relatively minor collection of domestic products that were used to build the self-anchored suspension span.

Inspectors have attributed the cause of the damage to the presence of hydrogen in the steel, a somewhat common phenomenon that causes the material to crack. Bridge officials have conceded the steel was faulty and that there should have been more oversight before the products were embedded into concrete on the span.

Goodwin said the bridge will remain committed to purchasing domestic materials for its public-works projects.

“There are questions about the degree of materials testing,” Goodwin said. “But this doesn’t push the needle one way or another when it comes to contracting with domestic firms.”

Gary Hubbard, spokesman for United Steelworkers, a union group that backed the Bay Bridge billboard campaign last year, said the workers at Dyson are not part of the organization’s membership. He said the group was monitoring news reports and investigating facts of the case.

Calls to Dyson on Thursday were not returned.

It is expected to take a month or two to fix the broken rods. The repair work could push back the opening of the span on Labor Day, although bridge officials have said that is unlikely.

wreisman@sfexaminer.com</p>Bay Area NewsBay BridgedevelopmentLocalMetropolitan Transportation CommissionPlanning