Recology in Snohomish is a waste collection vehicle maintenance facility that needed many structural elements repaired, reinforced, and, in some cases, replaced.
COLUMN REPLACEMENT
We replaced 21 columns that had rotted wood below grade. To accomplish this in an existing building, we first shored the building with scaffolding and temporary columns to support the structure before we removed the old columns. We then sawcut a 5′ by 5′ square in the 8-inch-thick concrete slab around each column and removed the concrete as well as the entire post. Then we excavated 5′ down to bearing soil to pour a “rat slab” at the bottom using fast-setting concrete. We then placed the new 10-inch by 10-inch by 24-foot tall, treated wood columns by rigging them with an all-terrain forklift. After each new 1,000-pound column was set and tilted into position, we connected it to the existing steel bracket at the truss and shimmed it with steel plates. At this point, the new column is inspected, and upon passing, the hole is backfilled with 5/8-inch clean chip rock, which compacts for structure, but also allows for water drainage.
Special Column Replacement
The steel upper connection bracket on one of the columns to be replaced was attached to a glulam beam, which went horizontally into more of the building’s structure. Removing the bracket or the glulam to install the new column would have opened up a much larger can of worms. The challenge was to install the replacement column into the bracket that already had through-bolts sticking out. This meant that we could not tilt the column into place as the existing bolts would not align with the column when it was at an angle. We had to find a way to bring the column vertical next to the bracket and then slide it horizontally into the bracket, all while remaining level and plumb. We matched the through-bolts in the bracket by creating a jig to know where to pre-drill holes in the new column. To add even more of a challenge, the through-bolts were not at perfect right angles, so the new pre-drilled holes also had to match the odd angles. Everything went according to plan during installation, and the column slid into the existing bracket without issue. Keep in mind that this is a 23-foot-tall 10-inch by 10-inch wood column weighing 1,000 pounds!
Truss Repair
Several of the existing roof trusses had been damaged by water over the years and had significant rot that needed to be repaired. The damage was to the bottom chord of the truss, which is made up of five 2-inch by 10-inch pieces of lumber bolted together. To replace the damaged pieces, we had to shore the roof and truss with scaffolding and a temporary column, then pull apart the chord to access the rotted pieces. The chord is constructed with the ends of each piece of lumber staggered from one another for strength, so the extent of replacement on each piece was different.
Truss Reinforcement
With an open height at the top of the exterior walls of 17 feet, the columns need a little extra stiffness to keep from shearing in the building’s North/South direction. We employed two methods to address this. The first is to add 10 10-inch by 10-inch wood beam angle bracing from column to truss, effectively reducing the height of each column. These beams are joined into the columns with old-school timber-framing notches. The second method of bracing was to the bottom chord of the trusses by sistering steel “c-channels” to each side, giving the trusses some much-needed support. Using two abutting lengths of C-channel on each side welded together (four total per truss) instead of one long piece on each side (two total per truss) was a significant cost-saving measure. In total, each side is 52 feet long and is connected with 70 through-bolts to tie everything together.
Truss Cross-Bracing
With the roof trusses now strong in their North/South direction, it was time to address the building’s shear strength in the East/West direction. The building’s original solution was horizontal steel strongbacks spanning from the bottom of one truss to the bottom of the next truss. While adequate, we were determined to do better. We helped develop a custom X-shaped design that has the added bonus of giving future trucks in each bay added clearance to raise their containers or loader arms for service. We then constructed and installed these between the six trusses, high above the warehouse floor.