Mushrooms any one? 3

[jheidt2543]

I am just in the begining stages of inpecting an existing industrial building that was constructed between 1900 - 1910 in the standard Mill Construction of the time. The roof framing consists of structural wood decking spaning 8' between timber trusses. The trusses are full 8x8 top and bottom chords with 8x4 compression web members and 3/4" steel rod tension members. Most of the building is in really good shape, but there are a few areas of concern where water leaks allowed the deck and some of the truss members to deteriorate.

One truss in question, from a side span of 21', has a large split on the bottom side of the top chord. Along the split is a large group (about 16&quot; long) of mushrooms some of which are about the size of my fist. I haven't check the moisture content of the wood yet, but the roof was fixed a few years ago and the building is dry now. The mushrooms don't seem to be growing any more and I don't think they are edible! <G>

I'm looking for information on the fungi attack of wood and what the structural implications are. Any help would be appreciated.

 

[ERV]

jheidt2543,

Fungus attack on wood structural members is like cancer. Fungus will remain dormant in the wood if no moisture is present, the re-introduction of moisture (min. 19%) will encourage new growth. The existing fungus in the wood will turn to dry-rot and significantly reduce the strength of the members affected (hence the rupture). The part of the fungus that is visible (the mushroom) is the tip of the proverbial iceberg, it is the roots that cause the damage to the cellulose fibers (they secrete enzymes that disolve the cellulose).

There is but one alternative; remove any fungus infested wood members.

 

[Qshake]

There was once a very thick publication on wood and timber bridges. I believe it was published by the Federal Highway Administration (FHWA) and have only seen it sporadically.

Why I mention it is the publication contained as much about timber deterioration as it did for design. I suspect this was appropriate for the inspection of timber bridges.

You may wish to check some university libraries, internet or the

http://www.fhwa.gov

for this text.

Good Luck.

 

[SlideRuleEra]

The publication that Qshake refers to may be the US Forest Products Laboratory's &quot;Wood Handbook - Wood as an Engineering Material&quot;. Chapter 13 has information on the deterioration that you describe. The handbook is available for free download (.pdf format) at:

http://www.fpl.fs.fed.us/pubs.htm

 

[aviat]

Fungi may, under conditions that favour their growth, attack the wood resulting in a condition designated as decay. Decay can occur at temperatures that favour growth of plant life in general. Serious decay occurs only when the moisture content of the wood is above the fibre saturation point (average 30 percent). These conditions are particularly prevalent in the South-eastern United States but may also be encountered in Canada. Only when previously dried wood is contacted by water, such as provided by rain, condensation, or contact with wet ground, will the fibre saturation point be reached. The water vapour in humid air alone will not wet wood sufficiently to support significant decay, but it will permit development of some mould. If excessive moisture is not allowed to enter the wood fibres, there is virtually no limit to the components' structural life expectancy.
From Appendix E - Inspection of Aircraft Wooden Components
Transport Canada.

 

[Qshake]

Right on the money slideruleera!!

Thanks!