Adaptive Re-use

August 28, 2008

America has a throw-away culture. It’s so pervasive that it’s hard to recognize unless you spend some time in another country. During several stays in Europe, my wife and I observed much more re-use of clothing, furniture, jewelry and even plastic grocery bags (in many countries, you have to purchase your bags). As a structural engineer, I was most impressed with the re-use of centuries old buildings.

The trend of adaptive re-use has caught on with a passion in Chicago. Soldier Field, the Chicago Bears’ historic stadium, is the most prominent example of such a project. Critics allege that new space-aged grandstands rising from within the classically styled colonnade create a post-modern eyesore. Nevertheless, the ability to re-use the site and adapt it to the requirements of a modern pro football stadium is impressive.

Such adaptations, albeit on a less visible scale, are happening all around the city. My first assignment upon returning home was the renovation of an old 1920s warehouse building into a high-priced loft condo development. Loft-style condos with high ceilings and exposed heating and cooling ducts have a strong appeal to the young professionals moving into the city.

The scope of this project involved designing new balconies, reinforcing the old load-bearing masonry walls, and evaluating and strengthening the existing heavy timber beams and columns for a change in occupancy. In the 90 years since the building was first opened, construction materials and techniques have changed significantly.

The old brick walls are up to five wythes (brick rows) thick. The original designers were caught in a Catch-22 when designing the walls. Load demands required thicker walls, but each additional layer further increased the load to the point where the self weight of the wall dwarfs the applied loads from wind and occupancy. At some point in the building’s life, stores opened up on the first floor and large store-front openings were cut into the walls on the first floor. Our investigation revealed that the narrow piers between these openings were overstressed according to the current code requirements. Instead of prescribing an expensive process of drilling into the existing pier to attach steel reinforcement, we opted to provide new steel posts to share the load from above.

The columns, beams, and flooring in this old warehouse were timber. The architects on our project really appreciated the aesthetic of the large timber elements and decided not to cover up the structure. Unlike steel, a homogeneous material with reliable strength, wood strength varies by species, quality and direction of loading. We called specialists to the site to visually grade the timber columns and collect samples to determine the species. For those columns that were given a poor grade, based on splitting, the number knots and other criteria, we developed a steel reinforcement detail. Because the columns were to be exposed to the occupants, we avoided clunky bolts that might protrude from the surface and present a hazard. Our solution included a combination of long wood screws and metal strapping like the type used to fasten traffic signs to light poles.

I enjoy working on renovation projects, because they present interesting challenges. The structural materials and construction techniques are rarely discussed in school, so you sometimes have to dig for information in old manuals or discuss the problems with other experienced engineers. The work may not be as glamorous as a brand new skyscraper but it is rewarding in its own way, and you can feel good knowing that you’ve contributed to the socially responsible act of re-using a “perfectly good” old building.

1 Comment
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