JAE
Structural
- Jun 27, 2000
- 15,463
We are looking at an old church, built about 1910, that has its main sanctuary roof framed with some wood trusses.
The trusses are of two kinds - one is a simply 2x truss with verticals and diagonals (all set on the flat - i.e. the truss was probably built on its side with 2x members laying flat) and nailed into the horizontal chords with
about 5 nails. These we call Truss type B.
Truss Type A is also made of multiple 2x wood parallel chords with vertical steel pipes (all in tension) and diagonal built-up 2x wood web members (all in compression). The diagonals simply are notched into the inside edges of the horizontal chord members and attached with some nominal nailing.
Both trusses, especially truss type A, have sagged about 4 to 5 inches and the plaster ceiling has some cracks that
have appeared in the last year or so.
The NDS 97 has some rough stuff in the appendix that discusses long term creep, basically using a factor of 2 on the sustained load deflections.
We haven't taken samples of the wood yet. Everything in the truss looks good (no dry rot, moisture damage, etc.) except for the fact that its sagging. All the joints and connections show no signs of slip or compressive distress.
Are there any specific articles, research, documents....or....your own experience...that you all could post here to add to my knowledge of this sort of condition?
The trusses are of two kinds - one is a simply 2x truss with verticals and diagonals (all set on the flat - i.e. the truss was probably built on its side with 2x members laying flat) and nailed into the horizontal chords with
about 5 nails. These we call Truss type B.
Truss Type A is also made of multiple 2x wood parallel chords with vertical steel pipes (all in tension) and diagonal built-up 2x wood web members (all in compression). The diagonals simply are notched into the inside edges of the horizontal chord members and attached with some nominal nailing.
Both trusses, especially truss type A, have sagged about 4 to 5 inches and the plaster ceiling has some cracks that
have appeared in the last year or so.
The NDS 97 has some rough stuff in the appendix that discusses long term creep, basically using a factor of 2 on the sustained load deflections.
We haven't taken samples of the wood yet. Everything in the truss looks good (no dry rot, moisture damage, etc.) except for the fact that its sagging. All the joints and connections show no signs of slip or compressive distress.
Are there any specific articles, research, documents....or....your own experience...that you all could post here to add to my knowledge of this sort of condition?
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