Sunday, February 10, 2019

What retired guys do when they are bored

There is something wrong in this picture. Can you see the welds that are missing?

The ever lovely and talented Mrs ERJ and I were in a very large (140,000 square feet) building yesterday. We arrived early and there was a lot of dead time between events.

Mrs ERJ caught me peering up into the steel-work. "Whatchya lookin' at?" she asked.

"Steel." I answered very truthfully.

Fixed-Fixed beams
Source of image

The roof trusses were designed as Fixed-Fixed beams. That means that the ends of the trusses transfer a bending moment into the supports.

The tell-tale is that the flange-plates for the top stringer are MUCH thicker than the flange-plates for the bottom stringer.
Flange-plate for bottom stringer.
The thicker plates are required on top because the stringer is in tension and all of the load must go through the plates.

The bottom stringer is in compression and nearly all of the load is transferred without creating bending loads in the flange-plates. They provide stability and ensure the ends of the butted up stringer beams do not shift.
The metal on the left side of the flange-plate is about 50% thicker than the metal on the right side of the flange plate. The height of the vertical portion is also much taller on the left.

Another clue is the beams are not as beefy further out on the span.

Did you find the defect?

It looks like this ear is missing a weld. All of the other ears that held strut-to-strut cross braces had welds to the vertical web, but not this one.

Don't feel bad. I had all day to look at this structure.

1 comment:

  1. Aaaah, "facilities guys"- always looking up. Sometimes carrying binoculars. Heh.