$6-6$ For an axial compression column $($ shown in Figure $6\mathrm{.}33),$ the length of the column is $7\mathrm{.}5m,$ and the two ends of the column is hinged. The bearing axial pressure design value is $N=1500kN($static load$).$ The steel material is Q$235$B$.$ The cross section is not weakened. Design the cross section of this lattice column:

$(1)$ lacing bar;

$(2)$ batten plate.

Figure $6\mathrm{.}33$ Exercise $6-6$