A
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Component Manufacturing dverti$er
Don’t Forget! You Saw it in the
July 2019 #11240 Page #32
Adverti$er
Compression or Tension Web Configuration—Which is Better?
O
n a recent Quality Assurance Audit at a large facility, we witnessed a floor truss builder carefully spacing out his floor truss webs in the allotted space available with precision and care. He was very meticulous. I asked him why he was doing that and he explained that his in-house inspector did not like any gaps in the webs. I showed him how he could adjust for this gap by tapping the webs away from the chase, widening the chase thus removing any gap. He then explained that, when he took that action, the truss salesmen would complain that the webs didn’t align. I commended the builder for his care and concern, but the situation revealed the need to discuss more issues during our review. When we sat down with the production manager, shift supervisor, and several other key individuals to discuss in depth the issues and problems we found, the following issues were in our discussion. 1.
Lumber dimensions will always vary slightly. It’s the nature of wood.
2.
Chord thickness change impacts the web location related to the length.
3.
It’s not reasonable to adjust standard web lengths to suit variations in chord thickness.
4.
Webs are cut with reasonable accuracy but the precision is not sufficient to assume all webs are equal.
5.
Hiding member to member gaps under the connection plate does not resolve the gap issue—it merely hides and obscures the problem.
6.
The Warren design of the System 42 truss accommodates the variability of the floor truss web lengths and the chord thickness variations as long as the chase width is flexible (in other words, that the chase can float).
7.
Gaps in a Warren configuration where the webs are designed in compression (see blue in diagram) can cause additional deflection in the floor truss as the truss is put into service.
8.
If the Warren configuration is designed in tension (see orange in diagram), this minor gap 0” to the maximum gap 1/8” will not add to deflection, because the connector plate will be designed to transfer the tension load.
9.
Holding chase sizes creates problems when sometimes the request is not justifiable.
10.
Tension web configuration can require a larger connection plate.
11.
Compression web configuration can result in a smaller plate.
Continued next page
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