Most engineering articles are about fancy and expensive new construction. It’s understandable for companies and engineers to want to share their experiences on once-in-a-lifetime projects. However, it’s usually the more mundane projects that keep the business profitable. Maintaining a strong business relationship with reliable clients can mean performing a lot of small jobs.
Our architectural clients also have to take on small jobs to keep their patrons happy. These projects often come in the form of tenant build-outs. When companies move into a new office space, they want to make their mark. If the office has multiple floors, the tenant will usually ask for a fancy monumental stair. Many modern offices also need to plan for large rooms to house computer servers and backup generators. Other, more traditional, office spaces require private libraries and high-density filing systems. Any of these conditions could overstress the existing structure.
Lately, I’ve been working on a lot of small tenant build-out projects. Sometimes, these can be quite challenging. On one recent job, the client wanted to install an artistically designed stair. The challenge was to determine where to place the opening and how to connect the stair to the slab in order to minimize the cost for the tenant. The design was further complicated because the floor was supported by a concrete waffle slab – so named because of how it looks. This type of slab was common in the 1970s to span long distances.
We determined that if the opening was located in the middle area between four columns, then no reinforcement would be required. The weight of concrete being removed offsets any additional load imparted by the stairs. Also, the reinforcement in that region was not essential to the overall stability of the slab. To connect the new steel stair to the concrete waffle slab, we detailed a connection involving welded steel plates and bolts drilled through the side of the waffle. On another job, for a new bank branch, we had to do the opposite: infill an old stair opening. The new tenant only rented one floor and needed a continuous space for bank patrons to meet with tellers and agents. We presented two options to our client. The first, more conventional, approach involved using expansion anchors to attach angle irons to each side of the opening. Then we called for steel metal deck filled with concrete to span between the angles. The disadvantage of this approach was that wet concrete would need to be delivered to the busy downtown site and then wheelbarrowed through the building’s atrium.
Our alternative design utilized thin sheets of structural concrete board – about the size and weight of a thick 4’x8′ plywood sheet. These sheets would span 18″ between light metal joists. Each of these components is light enough for a few construction workers to inconspicuously carry into the job site. We had to explain our concept to several reviewers, but the client eventually chose this option.
Not all projects are as glamorous as a record-breaking high rise. But even if a project doesn’t capture the imagination of the general public (or the engineering community), it may still be important for business and have interesting engineering challenges.