$18.$ What do Lr and Lp mean included.

The notation $L_p$ defines the maximum un$-$

braced length of the compression flange for which

the maximum design stress for a compact symmetri$-$

cal shape, $F_b=0\mathrm{.}9F_y,$ may be used. The notation $L_r$

defines the maximum unbraced length of the com$-$

pression flange for which the maximum allowable

bending stress can be taken as $F_b=0\mathrm{.}9(0\mathrm{.}7)F_y.$ This

denotes a $30\%$ reduction in the bending capacity as

we move to the limit of $L_r.$ Fortunately, the change