Has anyone seen a wood truss like this? 4

[albanyYEM]

I'm working on a multi-story building that was constructed in the early 1900s. Exterior walls are stone. Interior framing is wood joists with steel girders and columns. The roof is gabled with several dormers. In the attic, I ran into this wood roof truss with a pipe "hanger" (see pic) which appears to be missing a portion of the bottom chord in the center. However the "missing" segment of the bottom chord appears to be intentional and not a modification. I'm thinking that this was part of the original design and that the truss behaves in some manner that I'm not familiar with. It does not appear to engage the attic floor framing and seems to support only the roof. Has anyone run across a truss like this in their adventures?

 

[BAretired]

SLTA,

The answer to your question is unknowable.

BA

 

[KootK]

or was it built that way?

I'm voting for built that way. Of course, that's largely based on OP's read of the situation on the ground. While it's far from definitive, I note that the frame clearly never had diagonals. So while it may have been more convincingly tension tied in the past, it was never really a truss in the strictest sense.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[KootK]

Perhaps OP can provide more detail on the heel connection? If it was designed to transfer a bunch of thrust, it might telegraph in the joint detailing.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[KootK]

I suppose another possibility is that the rod and partial bottom chord are there simply to rectify the eccentricity between the bearing reaction and the delivery of the vertical component of the top chord compression. For this purpose, one might be able to theoretically do without the rods.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Teguci]

Definitely not ever a truss. Tie rods do little to nothing to keep the tension and compression chords apart and there is no evidence or room for compression web members. KootK's last sketch makes the most sense to me. Keep the connection into the stone wall from being eccentric and consider the diagonals and beam as a bent and not a truss.

 

[John2025]

Something heavy hanging from the ceiling downstairs, once upon a time?

 

[MikeHalloran]

Upon closer examination of the photos, I vote for 'not ever a truss'.
Note the flitch plates joining the 'top chords' in the second photo,
and a metal plate, or maybe a shingle, supporting the 'bottom chord',
and what I think is the end of the truss rod,
visible through the square hole in the floor, in the first photo.

Which leaves no explanation for the truss rods,
or the stubbed triple thick bottom chords,
or the triple thick beam resting on the top chord joints,
... except that something heavy must have been suspended there at one time, as conjectured.




Mike Halloran
Pembroke Pines, FL, USA

 

[OldBldgGuy]

I'm going to vote for "someone cut it out". I've crawled around in an awful lot of attics and seen a lot of stupid modifications that should have brought the building down but didn't, and this is actually one of the most common ones and can be old enough that it's hard to distinguish from the original tool marks. "Trusses" with the steel or iron hanger from top chord to bottom chord and either 2 or no diagonals, especially with the horizontal top chord, were pretty common, and so was some moron's assumption that the horizontal piece in the middle was simply an inconvenience. Of course, we could be the morons; the building is still working...