Lateral Torsional Buckling in a W section beam

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SUMMARY

The discussion centers on the design of a W-section beam under lateral torsional buckling (LTB) conditions in an Advanced Steel Design course. It is established that continuous lateral support negates the need to check for LTB, while for beams with lateral support only at the ends and at concentrated loads, calculating the Cb factor and the critical buckling stress (Fcr) is essential. Additionally, when the nominal moment capacity (Mn) exceeds the plastic moment capacity (Mp), the Mp value should be used as the governing nominal moment capacity, which must then be multiplied by the resistance factor (Φ) to ensure it exceeds the ultimate moment.

PREREQUISITES
  • Understanding of AISC Steel Manual design principles
  • Knowledge of lateral torsional buckling concepts
  • Familiarity with W-section beam properties
  • Ability to calculate Cb and Fcr values
NEXT STEPS
  • Study the AISC Steel Manual, specifically Equation F2-2 for moment capacity
  • Learn how to calculate the Cb factor for lateral torsional buckling
  • Research critical buckling stress (Fcr) calculations for W-section beams
  • Explore design strategies for beams with varying lateral support conditions
USEFUL FOR

Civil and structural engineers, students in advanced steel design courses, and professionals involved in the design and analysis of steel beams under lateral torsional buckling conditions.

Pooty
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Hey everyone, so I am in an Adv. Steel Design Course and I am supposed to design a beam under a given distributed DL+LL and Concentrated DL+LL. We are supposed to design the beam under two different conditions... a.) It has continuous lateral support b.) Lateral support is provided at the ends and at the concentrated load. So my question is for the condition a.), do we even need to check the beam for lateral torsional buckling? It seems that we wouldn't since it is braced continuously on it's lateral sides... And for case b.) we would need to calculate Cb and then Fcr to check LTB, right? Since these questions are not qualitative, I don't think I still need to show my work... Thanks guys.
 
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Your statements are correct.
 
When checking for lateral torsional buckling of a W-section beam, if your Mn value is greater than your Mp value (AISC Steel Manual Equation F2-2), do you have to choose a new W section or do you then just use the Mp value as the governing nominal moment capacity? Then multiply that by Phi and check that it exceeds your Ultimate Moment?
 

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