Ask the Architect

Still more on steel beams

Posted

Q. I read your column about steel beams, and was wondering about balconies on big buildings. I walk on the boardwalk in Long Beach several days a week, and see that some buildings are being repaired, exposing steel beams, especially the balconies. The beams are rusty but appear OK otherwise, even though they were inside cement. Does the cement protect them? Some beams look like they need replacing, and I wondered, since you wrote about fiberglass beams, why they don’t use them. I never saw a fiberglass beam.

A. Good question and observation. The repairs to buildings lining the boardwalk are a good example of what happens to steel that’s subjected to the elements — in this case, salt-laden air and moisture. The beams you saw were encased in concrete for many decades. I’m not sure whether they’re being replaced or buried again in concrete, so we’ll watch how they’re handled and learn collectively.
There are several points to be made in answer to your question. One is the misconception that covering something with concrete protects it from moisture, which it doesn’t. Concrete is like an absorbent sponge, drawing water in. Another is that there are many ways to build, and you’re seeing one choice made and learning how each step and each decision made in the repair process can have a lasting effect on the performance over the life of that building.
Observe how the exposed steel is cleaned, recoated or replaced, how steel is joined, welded or bolted, and whether finishes properly drain and dry or are left with pockets and slopes that allow water to collect and penetrate the outside coatings. Assumptions are often made that internal parts are protected from moisture without applying special coatings, and that buildings are only supposed to last a lifetime (a hundred years), anyway, when we have the technology and ability to build structures to last hundreds of lifetimes safely and effectively.

Fiberglass wasn’t an option 60, 70 or 80 years ago, when those buildings were being built. One reason it isn’t used more these days is lack of marketing and design information. Steel companies share information and processes, share data that leads to quality control and put out design manuals and computer programs. There are more than 10,000 different steel shapes, sizes and thicknesses to use, applying strictly regulated industry standards, and we use multiple engineering formulas for each beam to select the specific beam that meets each of the several calculated criteria. For example, a beam may pass the calculation for resistance to sagging, called bending moment, but not pass for sheer, which is the resistance to splitting or tearing. The fiberglass industry is much smaller, and the last time I called to discuss using fiberglass on a project, I couldn’t get data, sizing software, formulas, etc., and instead, an in-house engineer had to design and select what was needed, discouraging fiberglass use.

© 2017 Monte Leeper. Readers are encouraged to send questions to yourhousedr@aol.com, with “Herald question” in the subject line, or to Herald Homes, 2 Endo Blvd., Garden City, NY 11530, Attn: Monte Leeper, architect.