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Problem 9.3d : Roof-truss, Fink, snow load

  • Force P = 600 N
  • Length a = 4 m
  • Length b = 4 m

The above roof truss is exposed to a snow load. Somebody else has already determined what fraction of the snow lying on the entire roof has to be carried by the truss shown in the above figure, namely 2400 N (about 500 lbs). Because for the method of joints we have to assign these 2400 N to the individual joints the force P=600 N arises in the above figure assuming that the snow load is evenly distributed across the roof.

The Howe-roof-truss in Problem 9.3e has the same snow load (2400 N total), the same overall width (12 m) and the same height (4m). We want to do a bit of comparison as to the material needed for the construction, the largest tension, and the largest compressive force. On the basis of the results from both problems we might be able to judge which truss design is more advantageous.

Please determine :

  1. The sum of the lengths of all members

  2. In which member does the largest tension occur and what is its value.

  3. In which member is the compression largest, what is the value thereof and how long is that beam. The last point is of importance in order to judge whether buckling occurs or not.

Note : The member 25 is NOT perpendicular to the members 15 and 57. the anlog holds true for member 36.

My solution

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Zig Herzog,

Last modified : Sat Aug 09, 1997