A numerical study on lateral bracing of steel moment resisting frame beams

Date

2026-8-12

Author

Saltık, Heval

Metadata

Show full item record

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Item Usage Stats

59
views

42
downloads

Cite This

Beams of special moment frames (SMFs) are expected to sustain large inelastic rotations under seismic loading, while local buckling and lateral-torsional buckling may cause strength degradation. This thesis numerically investigates the cyclic lateral-torsional buckling behavior of stiffened and unstiffened I-shaped SMF beams under different lateral restraint conditions and evaluates the adequacy of the AISC 341-16 lateral bracing requirement. After verifying the finite element modeling approach, beams with different depths, member slenderness ratios, and flange and web width-to-thickness ratios were analyzed under unbraced and mid-braced conditions. Vertical stiffeners were placed within the plastic hinge regions to examine their influence on cyclic moment capacity and lateral-torsional buckling behavior, and the investigation was extended to beams with continuously restrained top flanges. The results show that vertical stiffeners improve moment capacity by limiting local buckling but do not consistently delay the first occurrence of lateral-torsional buckling. Mid-braced beams generally develop lateral-torsional buckling at lower slenderness ratios than the corresponding unbraced beams, indicating that cyclic lateral stability depends on the overall restraint arrangement rather than unbraced length alone. Lower width-to-thickness ratios substantially improve strength retention but have limited influence on its onset. Continuous top-flange restraint delays lateral-torsional buckling when the bottom flange is otherwise unrestrained, whereas its contribution is more limited when a mid-span bottom-flange restraint is present. Based on retaining at least 0.8Mp at θ = 0.04 rad and preventing visible lateral-torsional buckling, configuration-specific limiting Lb/ry values of 80–120 are proposed for the investigated beam groups.

Subject Keywords

Lateral-torsional buckling, Special moment frames, Cyclic loading, Vertical stiffeners, Lateral bracing

URI

https://hdl.handle.net/11511/120677

Collections

Graduate School of Natural and Applied Sciences, Thesis