In US engineering practice, "I-beam" shapes are usually W's not I's. W is for wide-flange. The W's are more efficient than the I's because the flanges are wider...to the point that I's are a specialty shape with specialty shape costs...at least in terms of availability/lead-time when structural steel is sold by the ton and probably a mark-up due to non-commodity status.
I had to search in Google, but IIUC the W-beams don't have the shape of a W. They look more like a rotated H.
Rather than looking at different letters, perhaps look at different font families. Clearly sans-serif I-beams are structurally much worse than avec-serif I-beams.
I don't know why "avec-serif" isn't the standard term. It should be.