Steel Design - Effective lengths of beams - Illustration example - SD424

This video is a simple example of how to determine and apply effective length factors to a steel beam.
Copyright Stellenbosch University

[@me09hha]

Well explained. Very clear

[@patocarrasco6266]

when you are so left handed that you can horizontally flip the surface you are writing on great video!!

[@joshvandermeer9138]

Hi Dr Wills, if the cantilever span has a midspan lateral support, how do you deal with the support conditions for each of the spans along the cantilever length?

[@firesun]

Always design between points of lateral support, with end conditions defined: (Section 1) ?Free tip, with ?only lateral support and continuous, and (Section 2) lateral support at tip and whatever conditions you have at support. Also, make sure you choose carefully between normal and destabilising load as that has a big influence on results.

[@picajoool]

@@firesun dr. Wills, can you recommend a good book on this topic with some solved egsamples? Thank you in advance

[@firesun]

@@picajoool In South Africa there is a textbook on SANS 10162-1 by Mahachi that can assist. However, most good steel design textbooks for university students should assist.

[@picajoool]

@@firesun Dr. Wills thank you for your response. Problem is that Im Eurocode based, but I love watching you videos. It seems that Eurocode doesnt have LTB effective lenghts defined for various conditions. It does have coefficient for effective lenght that you input in formula or finding out critical bending moment, but its not very intuitive and it doesnt have any explenation of dividing a beam into multiple segments between lateral supports, and checking each segment with its effective lenghts.....

[@user-qy3zo6dz5v]

Thank you for this helpful video. I had a question about destabilizing load. In the cantilever portion the load is on the tension flange and bottom flange is having bending compression. Will the load have stabilizing or destabilizing effect being on tension side?

[@firesun]

SANS 10162-1, which is probably the most codes, defines a destabilising load as being on the top/tension flange.

[@firesun]

Specifically in terms of cantilevers

[@Ash-tp3im]

Sir I am from India so I want to know that these values you are talking about are same to India code i.e IS CODE

[@kyleallan6181]

Prof, would the K value for section L3 not be 1.2? The section is laterally and torsionally restraint. If i am correct, a value of 2.5 is for only laterally restrained.

[@firesun]

L3 is a cantilever. On the right side it is free. On the left side it is continuous with lateral and torsional support. If assumed to be a destabilising load then we end up with K = 2.5.

[@chanbormey4499]

do we not consider the buckling on another axe?

[@firesun]

When considering a beam - it will only experience lateral-torsional buckling when undergoing bending about its strong axis. If bent about its weak axis it will simply yield without buckling occurs. Hence, beams only have one effective length and this is for LTB (except if the top and bottom flange both experience compression and have different effective lengths - but these are still both for LTB). Columns can have multiple effective lengths for buckling about different axes.

[@chanbormey4499]

@@firesun thank you .so for a beam has compresion force, we will consider it in interaction LTB and Buckling right ?

[@firesun]

@@chanbormey4499 - It depends on what you mean by compression force. (1) When a beam experiences bending the one flange will be in compression and the other in tension. Compression causes buckling. Hence, we focus on the flange which is in compression and its effective length. (2) If a beam experiences both a compression force and a bending force then refer to our other video which covers the design of such members - kzbin.info/www/bejne/jaPXpnyspLBliNU.

[@AjayInderchauhan]

Figure in front n person in back which type of screen is it

[@firesun]

Its a light board. Glass screen with light passing through it, that is picked up when you write with special pens.