In flexural buckling, the member deforms in a manner similar to bending, with the cross-sections displacing laterally without undergoing any torsional rotation. When lateral restraints are absent along the member's length, buckling occurs about the weak axis. For buckling to occur about the strong axis, sufficient lateral bracing must be provided to restrain weak-axis movement. 

Flexural buckling is most commonly observed in compression members, particularly columns. Since is directly related to unbraced length, structural designers use different methods to minimize this length to enhance stability and reduce the risk of buckling such as using additional beams or girders, horizontal or diagonal bracing systems, flange bracing.

Another reason for the difference in the weight of the designs by MkaPeb users and a few other engineers is using non-economical solutions such as additional beams or girders, while one of the most efficient and economical solution in portal frames and pre-engineering buildings, is using flange (fly) braces. 

https://pramotive.wordpress.com/2018/09/12/12-effective-length-of-braced-and-unbraced-column-what-and-how/

https://skyciv.com/docs/skyciv-member-design/general/unbraced-lengths-explained/

https://pbhgroup.in/pre_engineering_building.html


When flange braces are installed to connect the girts to the flanges of columns, they effectively prevent twisting and lateral movement of the column flanges. This bracing action reduces the unbraced length of the columns, thereby increasing their lateral-torsional buckling strength and overall stability. 

The figure below from the content of "Yura, and Helwig. 1995. BRACING FOR STABILlTY" illustrates how flange bracing reduces the unbraced length of the columns.

https://www.aisc.org/globalassets/aisc/research-library/bracing-for-stability.pdf  (PDF Page: 41/74)


Thus, this economical solution is used all over the world.

https://sankalpsystems.com/bracings/

https://www.eng-tips.com/threads/pemb-portal-frame-braces.407330/


MkaPEB strategically considers the flange brace as an essential element to prevent flexural-torsional buckling (FTB). By using flange braces in place of additional beams, girders, or horizontal and diagonal bracing systems, the total weight of the structure can be significantly reduced, resulting in a more economical design.


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