(photo by Timothy R. Smith) Six months into the construction of the future Walter Reed National Military Medical Center, Building A goes vertical.

About a quarter of the site has been prepped for the first floor, with either concrete placed or rebar laid in thick, iron grids.

To the untrained eye, it appears only a morsel of the project is complete, but Clark⁄Balfour Beatty is now preparing for the second floor.

‘‘Everything went well,” said Tim Weaver, a superintendent with the joint venture, overseeing the construction of Building A.

This week the form work for the columns will go in. Next week scaffolding will go up and, by mid-January, CBB will place concrete. It will move like a stairway, he said.

‘‘That’s how we’re actually going to pick up more time,” Weaver said.

The first pour on the second floor is slated for Jan. 12, a day later CBB will pour the 10th section of the first floor.

‘‘It’s just because the footprint’s so wide,” Weaver said.

Work is on schedule, thus far and the contractor, CBB, has poured more than 6,400 cubic yards of concrete, shot more than 1,800 tons of gravel, and worked more than 183,000 combined man hours.

Even with the vertical climb, some of the site is still exposed and recent cold weather conditions have not been agreeable, often causing delays. This poses possible problems for the new concrete on the first floor. To prevent any problems, CBB placed heaters under the scaffolding to warm the underside of the concrete.

‘‘If you’re below freezing for three days, you have to do something about your concrete,” Weaver said.

Concrete generates its own heat, the heaters just help it along. A clear plastic curtain, akin to a giant trash bag, descends from the first floor decking to the basement slab to trap the heat. The heaters are shut down over night, Weaver said.

There will be 12 pours per floor until they reach the sixth and seventh floors which are smaller. CBB is prepping those sites for concrete, which could be placed within two weeks.

The remainder of the basement level, still exposed, could be poured within two weeks. But first, CBB needs the ground to thaw sufficiently. They will then pour concrete for footings that serve as the base for columns. Before the slab can go down, the plumbers – currently installing piping in the dirt – must vacate the area.

The north portion of the site, adjacent to Building 1, is being prepped for walls. Large forms are in place to hold the concrete up while it sets.

The second of three tower cranes will be erected this weekend. The current crane has hoisted rebar around the site, lifted equipment and placed concrete for slabs and columns. The second crane will perform the same duties, but will cover portions of the site unreachable by the other crane. The final crane will be erected in the coming weeks.