SAN FRANCISCO (AP) — A second steel rod anchoring a tower along the new eastern span of the San Francisco-Oakland Bay Bridge failed a critical strength test, marking the latest problem for the replacement structure, a newspaper reported Thursday.

Caltrans officials acknowledged the issue Wednesday and added that 99 percent of the rods passed the tests, The San Francisco Chronicle reported.

Previously, 32 bolts that secure earthquake shock absorbers to the deck of the bridge cracked in 2013 after being tightened, threatening to delay the opening of the $6.4 billion span.

Tests found hydrogen had infected the bolts, making them brittle.

The cause of the recent failure will be determined by further tests in a materials lab. The three-member Toll Bridge Program Oversight Committee approved spending up to $4 million to study the latest issue.

Testing is expected in the next few days but it could take months to get the results. Toll-payer funds will be used to determine the extent of the problems.

The problem could have been caused by threads that were stripped during installation, by corrosion from sitting in water, or both, Caltrans’ Dan McElhinney told the newspaper.

Meanwhile, “this bridge is safe, and it’s going to perform well in a major seismic event,” McElhinney said.

The new span opened in September 2013, replacing one built in the 1930s that was damaged during the 1989 Loma Prieta earthquake.

The three-member Toll Bridge Program Oversight Committee approved the funding earlier this month after an anchor rod in the bridge’s tower failed a test and salt was found in other parts of the tower.

The new bridge is intended to replace a span that was not considered earthquake-safe.