At joint (4) there are four forces, all known except the one in i.e. EF, FG, and GH represent the first three; hence the line joining I and E must represent the stress in ie. This line, if the drawing has been correctly and accurately made, is parallel to ie.

* Rollers to allow for free expansion and contraction of the truss would not be required for one as short as this. They are not used generally unless the truss is 55 feet or more in length.

For wind on right side, BC, CD, and DP Fig. 29(c) represent the loads at joints (3), (5) and (6) respectively and PE and EB the right and left reactions; then BCDPEB is the polygon for the loads and reactions. The point B is also marked A and O because there are no loads at joints (2) and (1).

The polygon for joint (6) is DPEID, EI and ID representing the stresses in ei and id respectively. The polygon for joint (5) is CDIHC, IH, and HC representing the stresses in ih and hc respectively. The polygon for joint (3) is BCHGB, HG, and GB representing the stresses in hg and gb respectively. The polygon for joint (2) is BGFAB, FA representing the stress in fa, and since GF equals zero there is no stress in gf

At joint (1) there are three forces, the left reaction, AF and the stress in fe. This third force must close the polygon, so we join F and E and this line represents the stress in fe. If the work has been accurately done, FE will be parallel to fe.

Fig 50.

Example For Practice

Analyze the truss represented in Fig. 26 for wind pressure, the distance between trusses being 15 feet. (See Ex. 3, Page 27, for apex loads.) Assuming both ends of the truss fastened to the supports, the reactions are both parallel to the wind pressure and the reaction on the windward side equals 6,707 pounds and the other equals 3,053 pounds.

Ans. Stress Record for Wind Left.