The limited no of rolled steel section are available in market.The radius of gyration in minor axis is in small giving large slenderness ratio with the result design stress get sufficiently reduce making the section uneconomical

Further the rolled steel section do not have sufficient strength to resist heavy load in such cases .The section are fabricated consisting of two or more individual section such as channel angle, I section etc properly connected along there length by Lessing & battening so that they act together as I u it . They are called as built up section

All built up section should prepractically be so proportioned that slenderness ratio about both principle axis are the same

Design procedure

Step1 Design column section using channel $\lambda =1.05\lambda e$

Step II. Providing spacing

Spacing between two channel

Ixx=Iyy....[Is pg 48 clause 7.6.1.1]

Step iii.

a) Angel of inclination. 7.6.4

b) Width of lacing 7.6.2

c) Thickness of lacing

d) effective length

e) Radius of gyration of lacing

r min= t/ $\sqrt{12}$

f) Spacing distance between lacing points

Step iv

Check for compression

Step v

Check for tension

Step vi

Bolted connections

Step bio design the plate

Note - same step for weld but parameter which depend upon left off lacing will be changed