How to prevent lateral torsional buckling without using lateral bracing

Talking about the most used wide-flange section as a beam member, lateral torsional buckling problem is always accompanied. In general, this problem is solved by using lateral bracing. However, the additional bracing reduces the usable space in a building. Therefore, there is a significant advantage that can be achieved if the need for lateral bracing can be eliminated while ensuring the stability of the beam with another method. In fact, the lateral torsional buckling can be easily eliminated if additional side plates are added to the wide flange beam. However, the cost will greatly increase. A more efficient way to take advantage of adding side plates should be sought. The possibility that the side plates are only needed at a certain location in the beam where the moment demand is higher exists.

To this note, scientists at National Taiwan University of Science and Technology: Prof. Cheng-Cheng Chen, Dr. Erwin, Charles Julius Salim, and Rudy Tiara investigated the seismic performance and lateral torsional buckling behavior of beams partly covered with side plates under cyclic loading both experimentally and analytically. The side plates are only provided at around beam end where moment demand is the largest under seismic loading. They evaluated the effectiveness of using side plates to prevent lateral torsional buckling and also to develop a design guideline for wide-flange beams covered partly with side flanges. Their research work is currently published in the research journal, Journal of Construction Steel Research.

Briefly, the author commenced their experimental work by investigating the lateral torsional buckling behavior of wide-flange beams partly covered by side plates supported laterally at the top but not at the bottom. They tested several cases comprising of beams with and without side plates and compared their performance and behaviors in terms of ductility, strength, and lateral deformation. Furthermore, a finite element model was developed and verified using the obtained test results.  Eventually, a design guideline was proposed based on the obtained results.

The authors observed that the additional side plates with suitable length to a beam near both ends were ideal for suppressing the lateral torsional buckling even no lateral bracing is presented at the bottom flange. For instance, the performance of the beam significantly depended on the length of the side plates. On the other hand, the required side plate lengths were influenced by the beam total length, dimension and yield strength of side plates, and beam section properties including the depth-width ration, width-thickness ratio of flange and web.

As a successful contribution of the study, a design guideline was proposed that establishes the required side plate length as a function of the previously mentioned parameters. This will enhance the seismic performance of beams with side plates thus ensuring the security of the building and other structural components.