A compound steel column consisting of $$2$$ $$ISHB$$ $$400$$ placed at $$320$$ $$mm$$ centers, carries a total axial load of $$2500$$ $$kN.$$ Minimum slenderness ratio of the compound column is $$30.$$ Width of the flange of one $$ISHB$$ section is $$250$$ $$mm$$ and its minimum radius of gyration is $$51.6$$ $$mm$$. Design a suitable single flat lacing. $$20$$ $$mm$$ diameter single rivet is used to connect the lacings to the column. Rivet capacity need not be calculated. The following table may be used.