Steel Buildings in Europe

Part 4: Detailed Design of Portal Frames 4 - 80 C.3.2 N crT for uniform members with discrete restraints to the tension flange The elastic critical buckling force for an I section with intermediate restraints to the tension flange is given in BB.3.3.1 as:            t 2 t w 2 2 t 2 z 2 2 crT 1 GI L EI L EI a i N s   where: 2 2 z 2 y 2 s i a i i    L t is the length of the segment along the member between torsional restraints to both flanges a is defined in C.1. For tapered or haunched members, N crT is calculated using the section properties of the shallow ends.