The oversized loads came by truck, hauled not by 18-wheelers, but 50-wheelers.

Their cargo — three huge steel beams — were slowly lifted by a massive floating crane from a Canton Industrial Area pier onto a waiting barge on Monday. Those beams’ arrival marks a new step in building the replacement Francis Scott Key Bridge spanning the mouth of the harbor.

Construction of the bridge is expected to begin later this year, but before that can happen, engineers need to test cylindrical piles — long, hollow columns driven deep into the riverbed — to make sure they’re strong enough to support the bridge.

The hefty pieces that came Monday are components of a massive frame that will be placed atop the test piles, allowing engineers to record relevant data and observations.

“The load frame will be used to test the soil properties by applying a significant weight over a period of time,” Maryland Transportation Authority spokesperson John Sales said in a statement Monday.

Hours before an explosion on a cargo ship near the bridge site Monday evening, it was business as usual in the port.

Workers fastened one of the steel pieces to thick cables attached to the floating crane called The Baltimore, owned by McLean Contracting. The Baltimore participated in the cleanup from last year’s deadly bridge disaster.

The crane lifted each beam off the truck bed and rotated it onto a barge, which will carry the pieces to a nearby yard where the frame is being assembled, according to the authority.

W&W|AFCO Steel, a massive American steel company, fabricated those steel pieces in Colfax, North Carolina, and Van Buren, Arkansas.

The test frame that they form won’t be a component of the new bridge, but rather a mechanism to test the supports. Still, it represents an essential step — in a journey full of them — as the state, in conjunction with contracted builder Kiewit, moves toward construction.

The bridge is expected to cost between $1.7 billion and $1.9 billion and be complete by October 2028, although state officials have cautioned that the cost and timeline will be updated soon.

The piles will be 8 feet in diameter and as long as 220 feet. Test piles are being fabricated in Texas and will be installed in September, the authority said; at that point, the load test frame will be used to analyze the piles’ strength.

The original Key Bridge, completed in 1977, was knocked down last March by the wayward container ship Dali after it lost power. The collapse killed six men, temporarily choked off shipping to the Port of Baltimore, and launched a flurry of lawsuits against the ship’s owner and operator, the state of Maryland and Hyundai, the ship’s builder.

Demolition of the bridge’s remaining structures — which still sit in the Patapsco River — began last month, and will continue until the first part of next year. Construction, however, can begin before the demolition is complete.

Due to debris from the collapse lodged beneath the mud line, the bridge will be built 260 feet east of where it initially had been planned. Because of that, the rebuild must seek amendments to the permits it received. On Wednesday, the Maryland Department of the Environment will host a hearing regarding that modification.