Lateral torsional buckling of open cross-sections with lateral and torsional restraints

Lateral-torsional buckling (LBA) resistance often governs the design of open-section beams. It can be greatly increased by taking into account restraints provided by a floor or a roof, typically a sandwich panel. LBA resistance is compared on IPE-section and cold-formed C-section.

Concrete floor, if connected to beams by shear studs, effectively restrains lateral-torsional buckling of these beams. Trapezoidal sheeting or sandwich panels typically connected by self-drilling screws do not have sufficient strength and stiffness to restrain lateral-torsional buckling completely. But they may help up to some point. How this lateral-torsional restraint is applied is described in this article.

In this thorough study by authors from ETH, Zürich, the results of three software of linear buckling analysis are compared: LTBeam, Abaqus, and IDEA StatiCa Member. The differences are discussed and explained. Furthermore, the results of geometrically and materially nonlinear analysis with imperfections of two software are compared: Abaqus and IDEA StatiCa Member. LTBeam does not have this functionality.

Two cross-sections are investigated:

  • IPE 240
  • CFC265x65

Three types of restraints at the top flange are investigated:

  • Lateral (shear) restraint
  • Torsional restraint
  • Combination of lateral and torsional restraint

Two types of loading are considered:

  • Uniformly distributed load
  • Force at mid-span

Two types of boundary conditions:

  • Fixed
  • Pinned

Conclusions

  • Linear Buckling Analysis (LBA) simulations show good agreement for low values of restraints for all three software; however, at higher values of restraints, LTBeam diverges. This is caused by a large simplification: the cross-section of LTBeam that uses 1-D element cannot deform. IDEA StatiCa Member with Abaqus shows good agreement in critical buckling factor.
  • Geometrically and Materially Non-linear Analysis with Imperfections (GMNIA) again shows good agreement between IDEA StatiCa Member and Abaqus (maximum difference of 5%).


The full report is attached.


Author: Andreas Müller M.Sc.

Responsible investigator: Prof. Dr. techn. Andreas Taras

ETH Zurich, Institute of Structural Engineering (IBK)

Attached Downloads

Related articles