Historic Mill Building Beam
Historic Mill Building Beam
(OP)
I'm hoping someone here can shed some light on a framing system I saw in a mill building recently. The mill is located in the Northeast. Bascially, the beam/girder consists of two 3x or 4x members with a tie-rod in the middle. The tie rod projects well below the wood members (say up to 2' in some cases where it is a girder) and has a turnbuckle in the middle. Steel posts attach the rods to the underside of the wood members. I have attached a photo. This particular mill had these members acting as beams in some cases and beams/girders in others. Anyone know what this framing system is called and where I can get more information on it?





RE: Historic Mill Building Beam
With today's more modern materials and practices - these have gone by the way side.
Just analyze it as a truss - inverted. Close enough. Knowing the wood and steel values is however somewhat hard to figure. I would give the wood about 1000 psi Fb and the steel about 30K tension
RE: Historic Mill Building Beam
The official name is a "Queen-Post Truss". If it had one post in the middle it would be a King-Post truss. Early (100 years ago) all railroad cars were constructed with wood floor beams and iron or steel queen post trusses.
RE: Historic Mill Building Beam
RE: Historic Mill Building Beam
RE: Historic Mill Building Beam
RE: Historic Mill Building Beam
Didn't much help the Hartford Civic Center - kinda like putting a bandaid on a gunshot wound.
This is an early example of post-tensioning a structural member - intuitively it makes sense, though I'm not convinced every application was thoroughly analyzed - it was an effective way to mitigate deflection.
The Bissell Bridge over the Connecticut River had a similar technique applied after the DOT realized the existing prestressed girders were deteriorating. A short-term fix for poor quality control. The bridge has since be replaced.
Ralph
Structures Consulting
Northeast USA
RE: Historic Mill Building Beam
In the interest of completeness, do you have a reference stating that cables were installed to reduce the deflection in the Hartford Civic Center? Having read all about that collapse, I don't recall that they tried such a scheme.
RE: Historic Mill Building Beam
RE: Historic Mill Building Beam