Structural Engineering & Statics
where the load goes
Ladder

Chevron brace — the ladder

One essay so far against this idea. A ladder is the distinct arguments that stand against one idea, and this one has room to grow.
  1. The two braces balance until one of them buckles. An inverted-V brace after the compression member has gone. While both braces are elastic they carry equal and opposite forces and their vertical components cancel on the beam above, which is why the beam in a chevron bay is usually sized for gravity alone. The compression brace buckles at 527 kN and then sheds most of what it was carrying — 30% is left here — while the tension brace goes on to yield at 1207. The difference between the two vertical components is 742 kN, applied at the middle of the span with no help from either brace, and it asks the beam for 1483 kNm against the 200 kNm the gravity load asks for — 7.4 times as much. The beam drawn does not: 1683 kNm against a capacity of 731. The force is not a load case anybody applies; it is what the frame leaves behind on its way to the state it will actually be in.

    The force the brace leaves behind

    Two braces meeting under a beam carry the storey shear as a tension and a compression whose vertical components cancel, so the beam above sees nothing. They cancel only while both braces are elastic. Once the compression brace buckles it sheds most of its force, the tension brace goes on to yield, and the difference is a point load at midspan that nobody applied.

    rung 1 · structures

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