18 22 26

Diameter ratio, fi

FIGURE 30.7 Values of Qq for axial load in X connections and other configurations subject to crushing.

30.8.1 Joint Efficiency

The importance of branch/chord thickness ratio tau (t/T) and of angle (sin d) becomes apparent in the expression for joint efficiency, Ej, given by

where Qf is the derating factor to account for chord utilization (described in Section 30.8.2), and the ratio of specified minimum yield strengths Fyo/Fy drops out if chord and branch are of the same material. In LRFD, joint efficiency is the characteristic ultimate capacity of the tubular connection, as a fraction of the branch member yield capacity. In ASD, joint efficiency is the branch member nominal stress (as a fraction of tension allowable) at which the tubular connection reaches its allowable punching shear. Connections with 100% joint efficiency develop the full yield capacity of the attached branch member, in either design format.

3 Ph

Diameter ratio, fi y = 8 10 14

0 0

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