INDIANAPOLIS -- Federal investigators are headed to the site of Thursday's massive tanker fire and explosion on Indianapolis' northeast side.

A three-member team from the National Transportation Safety Board will join the investigation into how a tanker truck hauling liquid propane crashed, caught fire and exploded, damaging bridges spanning both eastbound and westbound lanes on Interstate 465 Thursday morning.

Friday afternoon, Indiana Department of Transportation officials reopened I-465 westbound at Interstate 69 after the westbound bridge was deemed structurally sound for traffic. The Binford Boulevard northbound ramp to I-465 westbound was also reopened.

More than a dozen structural engineers from INDOT, Federal Highway Administration and Purdue University, along with private contractors, were at the site Friday testing steel bridge beams that may have been damaged in the blast, which sent flames hundreds of feet into the air.

"Heat such as this has the ability to change the structural properties of the steel," said INDOT spokesman Will Wingfield. INDOT officials said they want to reopen I-465, which averages 150,000 vehicles a day, as soon as possible, but won't do so if the bridges are not safe.

Workers began drilling 3-inch pieces of steel out of the horizontal beams. They will collect 14 samples, along with four bolts, and take them to a lab for strength testing.

The samples are being taken from the most- to the least-damaged portions of the bridges.

Even if long-term repairs are needed, Wingfield said it may be possible to reopen at least one of the bridges to through traffic relatively quickly.

"It really just depends on how quickly the lab can get that turned around," Wingfield said. "Hopefully, through the weekend and Monday, we might be able to get those results back, and based on their findings, hopefully reopen portions of one or both bridges."

Of 45 concrete pier columns that support the bridges, one was knocked out, Wingfield said, and will have to be replaced with new supports.

INDOT released this list of the ramps still closed in the area of the busy interchange:

I-69 southbound ramp to I-465 southbound

I-465 eastbound ramp that loops down to enter I-69 northbound

I-465 eastbound ramp to Binford Boulevard southbound

I-865 southbound to I-465