Ask the Architect

A rusted beam, Part 2

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Q. We don’t live near the ocean, but a recent engineer’s report, for the people who were going to buy our house, said our support beam was rusted. He didn’t recommend that it be changed, from what we know, but it scared them off. We looked at it, and even though it is rusted, it doesn’t look any different than our next-door neighbor’s, and he tells us everyone’s beams are rusted. So we looked around our neighborhood, and they’re all rusted. Should we be concerned? When is a beam too rusty, and is there anything we can do about it now? Also, if we have to replace it, should it be “galvanized,” as the engineer wrote in his report?

A. Continuing from last week’s column: When the landlord refused to replace or have anything to do with the replacement of a basement main beam supporting a retail store, testing was done, using sounding and X-ray, because I could put my finger through the badly corroded beam. Some portions were sound, while other areas, in the center of the vertical face, were paper-thin from years of exposure to dry-cleaning chemicals.

The key to deciding what to do with a rusted beam is to understand the extent of thickness of the vertical area, called the “web,” and to make sure the horizontal, flat top and bottom sections are uninterrupted — no kinks, cuts or breaks. When you look at the ceiling in a big-box store, the kind where the ceiling structure is open and exposed, notice that the lattice structure has triangular rods or struts welded to horizontal runners. These configurations of trusses, also used on some bridges, are also as strong as a solid beam, but much lighter, and have openings through 90 percent of their whole composition. The openings in the steel beams and trusses are located without interfering with the ability of the load on the beam (or truss) to transfer from the top part of the beam diagonally down one of the angled struts.

In the same way, a beam transfers loads from the top area to the bottom area. As long as there’s enough material in the beam, it can still hold the load and transfer it to the bottom of the beam. This is an important part of what the beam does, because the strength of the beam, and its ability to carry a really heavy load, depends on how high the top of the beam is from the bottom. So an 8-inch beam is weaker than a 12-inch beam, no matter what length it spans.

If the beam has plenty of material left, and only its surface is rusted, it can still support loads. Galvanized beams are recommended in areas exposed to corrosive forces, like chemicals or salt air, but the hot dip plating process adds considerably to the cost of the beam and isn’t necessary. Good luck!

© 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.