Attaching lumber. Working in the shop, we drilled pairs of 9/16-inch holes on 16-inch centers through the beam webs for through-bolting 2x10 packing. The packing provided nailing for joist hangers on the interior and cladding on the exterior. We fastened most of the packing to the beams while they were still on horses at the shop — which is a lot faster and safer than doing it on site from ladders 20 feet off the ground.
Though you can use powder-actuated fasteners for attaching plates to the flanges, I prefer to use screws, since the lumber occasionally needs to be temporarily removed to provide clearance for welding.
I use the baseplate patterns to locate the anchor bolts for columns. I ran a 3/16-inch masonry bit in a cordless hammer drill through the holes in the pattern to mark the concrete, then followed with a hammer drill and a 9/16-inch bit to expand the holes for the 1/2-inch-diameter threaded rod. I used two-part A7 (800/348-3231, itwredhead.com), a fast-curing acrylic adhesive, to set the bolts. To hold the alignment while setting the rods, I used the third copy of the pattern with its holes enlarged to 9/16 inch. Once the adhesive solidified, I leveled the setting nuts to receive the baseplates.
We stood all of the first-floor columns by hand in about three days, spending about a half-hour setting each one. We used the setting nuts to plumb the columns and set them generally level to a laser dot by measuring down from the column tops.
To attach the headers above the sliding doors to the columns, we shop-welded flanges at a uniform distance down from the top. To avoid potential cumulative dimensional errors, we decided to install these headers only after setting the top perimeter beams and welding them to the columns. The headers were made up of double, 11 1/2-inch-wide LVLs, faced on the exterior side with 2x12s to pack them out to the building line.
It’s important to educate everyone on site about the hazards of working around a crane. There is always the risk a beam might slip from its sling, so everyone needs to stay focused on the load and stay out of the fall zone. At least two of the crew should be familiar with the hand signals used to guide crane operators. If the operator’s line of sight is blocked, one person must be in view of both the operator and the workers receiving the beam. The deck needs to be clear of debris and obstacles, with pipe staging and stepladders arranged and ready.
Before the lifting starts, we use powder-actuated nails to fasten 2-by cladding to the outside faces of the corner columns so we can attach temporary braces for steadying and plumbing the frame as it goes together. On this job the GC, Art Hultin, provided us with dozens of adjustable concrete form braces. These can’t be beat for quick fine-tuning during assembly.
Setting beams. Beginning at a corner, we set the first perimeter beam and tack-weld it to the column. A tack weld is about 1/2 to 1 inch long. That’s long enough to hold, but not so long as to require extensive grinding to remove in case of error. The square cut on top of the column is no guarantee that the beam sits plumb, but if a web isn’t plumb, we’ll have trouble lining up holes between the connecting members. So while the welder tacks the column, a helper pulls the beam plumb using a bar clamp or a wrench as a lever. Since the action of welding tends to forcefully pull pieces toward the weld, the first tack goes on the side of the beam that needs to move down.
Next, we tack the corner column at the other end of the beam, and then take a moment to check our bracing. Each time you lower a beam into position, it acts like a wrecking ball to pound the framework out of plumb. To keep tabs, I use a PLS5 vertical laser to project a dot from the chalk lines on the floor. We adjust the braces until the dot streaks the edge of the 2x6 plate on top of the beam. This takes only a few seconds and ensures precise alignment.
As we work our way around the building, we inspect for a consistent TOS. Just as with framing lumber, one steel beam of a stated height may be slightly shorter or taller than the adjacent one. We can still adjust the columns up or down on the setting nuts to maintain a consistent top alignment.
Once most of the beams are on columns and tacked, we finish the welds and tighten the nuts and bolts at all connections, using a socket wrench on a cordless impact driver. This is a lot faster than tightening by hand and ensures that each bolt is tightened with equal force. Even though the bolted connection is engineered to stand alone, we still weld a few inches of bead along each angle clip to eliminate even the slightest movement in the connection.
Packing the baseplates. With every beam leveled, bolted, and welded, I grout the voids under the column baseplates, using hydraulic cement. Because it sets so fast, I mix the cement in small batches. I premeasure the powder, use ice water to give me a little more working time, and mix the material to a stiff consistency. I wear good nitrile gloves and pack the cement with my fingers under the baseplate and around the bolt shanks. It’s faster and more thorough this way, and it saves me from having to clean tools later.
Before tackling this building’s second-story steel, we installed the roof I-joists and plywood decking. The frame shook noticeably while we were slamming the pieces of lumber into place, so we kept the braces on the columns for the duration. Once the roof diaphragm was completed, though, most of the shaking disappeared.
The second-floor steel installed much like the first, except that the columns were 2 feet shorter and bolted directly to the first-floor beams. At all column locations, whether above or below the beam, we welded stiffeners to the web. Without these stiffeners, the beam flanges would distort when they were welded to the column and throw it out of plumb.
Since the top of the first-floor beam was completely level, we didn’t need setting nuts on the upper floor. Instead, we used stainless steel shims to plumb the second-floor columns. We buy these shims in an assortment of thicknesses — down to 1/1,000 inch — from Manhattan Supply (800/645-7270, mscdirect.com).
With the second-floor frame fully assembled, the bolts snugged tight, and the welded connections complete, we welded the bolted baseplates to the beam flange. Structurally, these welds were redundant, but we knew that they would take a small but perceptible amount of shimmy out of the frame.
Overhangs and Cantilevers
The roof over the second floor was designed with a 7-foot overhang hovering above a rooftop sun deck . The overhang was supported by three projecting W10x22 beams, with wood I-joists filling in between, parallel to the face of the building. Steel beams and moment connections perform exceptionally well under these conditions, ably resisting both sagging and wind uplift. In my experience, long overhangs framed with wood develop problems, often right from the beginning. Steel is the way to go.
The trellis structure on this house incorporated a true cantilever: Level channel struts projected several feet from the building and were simply welded to the face of the steel columns. This type of right-angle joint isn’t possible to execute in wood.
Considering both the recent doubling of the price of steel (along with every other metal) and the fact that this building couldn’t be built using conventional wood framing techniques, there’s not much point in making a direct cost comparison. However, for the record, labor and material costs for the rough framing ran about $175,000, or $53 per square foot.
Ed McPartland is a framing carpenter in Wellfleet, Mass.