Another structural question
Those are the fun one’s.
Mind benders sometime’s but keeps one on his toes.
The correct answer ic C. More info is available here:
Explanation of a Pick Test
From a structural engineer’s point of view, the design and construction is only valid for future service if the material is in its original condition, free of degradation. There are several factors that degrade the state of the lumber used, including fungal decay. The “pick test,” described below, is based on toughness and has been proven to detect decay with as little as 5 to 10% weight loss (Wilcox, 1983).
Decay Detection using the Pick Test
Fungal decay is common in areas near fasteners, joints, checks, end grain, paint discoloration and where lumber and timbers are near or in contact with soil. The “pick test” uses an ice-pick tool to penetrate the wood surface. Other tools such as an awl or even a small screw-driver can also be used.
After penetrating the wood, the tool is rotated to pry a splinter, parallel to the grain, away from the surface. The appearance of the broken splinter is used to determine if the piece is decayed. Since different species have different densities and all lumber is affected by its environment, trying the pick test in an area where the wood is known to be sound would be a way to determine a “control” for the rest of the inspection. The test should be conducted in a latewood zone (the darker, thinner growth rings), although the test also may work in early wood zones. The testing should begin in areas that are conducive to fungal decay, noting how much pressure is required to penetrate the surface. The depth should be about 1/4 in. A small amount of the surface wood should be pried out and compared to the results of the non-decayed wood.
Wilcox (1983) identified three distinct modes of failure for decayed and non-decayed wood. Non-decayed wood will generally fail with either a fibrous failure or a splintering break as shown in Figure 1 and 2. Decayed wood will have a brash, brittle failure with breaks directly over the tool. Very few splinters, if any, will appear and the break will be across the grain as shown in Figures 2 and 3. Figure 1 and 2 were taken in a salvaged Douglas Fir log yard. In the Figure 1 and 2 examples, the wood is weathered, and to the inexperienced eye they look the same.
Figure 1 The sound wood broke in a solid piece, and far from the tool. It was difficult to penetrate deeply. One end did not break at all. The wood under the splinter is intact and looks new.
Figure 2 The decayed wood broke easily; the break is across the grain with no splinters.
In a fibrous failure, the splinters are long and separate out of the surface far from the tool as shown in Figure 3 (Virgin Douglas Fir). A splintering break typically occurs directly over the tool with numerous splinters. It is possible that the wood is very dense and in such good condition that penetration is difficult. Also noticeable with sound wood is the noise associated with the break. In non-decayed wood, the sound will be as expected when wood breaks. However, with decayed wood, the breaking noise will not be as loud, or there may be almost no audible sound.
Figure 3 This example is a block of virgin Douglas Fir with no decay. It shows a splintered break that begins far from the penetration.
Figure 4 On the surface, this 50-year-old Douglas Fir purlin looked sound, however with the pick test, decay is indicated by a brittle cross grain break directly over the tool. The entire break is less than one inch long.
The pick test is a simple, subjective test that is useful to detect decay near the surfaces of wood members. With experience, the user will be able to identify fungal decay more readily and detect the subtle differences between the decayed and non-decayed areas. For inspections where only knowledge of the presence of decay is needed, such as residential decks, the pick test is useful. For the case of a residential deck or balcony, we recommend wooden members be replaced if any decay is detected. If the lumber is not pressure preservative treated (PPT), this fact should be considered when making the decision to replace the elements.
There, I finally got the photos to upload - sorry for the delay
Good work and good research.
Thanks for the information.