2017 Annual Stability Conference Presentation
Vinnakota Award Winner – Alireza Farzampour 

Session S10 – Stability of Plates
Friday, March 24, 2017
8:00 am

Lateral Torsional Buckling of Butterfly-Shaped Shear Links

A promising type of hysteretic damper used for seismic energy dissipation consists of a set of butterfly-shaped links subjected to shear deformations. Prior research has been conducted on shear panels with straight links, also referred to as steel slit panels or slit steel plate shear walls. Butterfly-shaped links have been proposed more recently to better align bending capacity with the shape of the moment diagram. The links have linearly varying width between larger ends and a smaller middle section.  These links have been shown in previous tests to be capable of substantial ductility and energy dissipation, but can also be prone to lateral torsional buckling.  In this article, the lateral torsional buckling of a butterfly-shaped link subjected to shear loading is conceptualized, and differential equations governing the links’ buckling behavior are formulated. The differential equations are numerically solved for a useful range of link geometries. The resulting critical moment, and related critical shear, are provided in a useful format for use in butterfly link design. Strategies for controlling lateral torsional buckling in butterfly links are recommended and are validated through comparison with finite element models.

Alireza Farzampour and Matthew R. Eatherton, Virginia Polytechnic Institute and State University, Blacksburg, VA

2017 Annual Stability Conference Presentation

Session S1 – Stability of Steel Bridges
Wednesday, March 22, 2017
8:30 am

Behavior and Design of Non-Composite Non-Longitudinally Stiffened Welded Steel Box Section Beams

The current AASHTO LRFD provisions for flexural resistance of non-composite non- longitudinally stiffened, welded steel box section members have a number of limitations. The current AASHTO Article 6.12.2.2.2 does not address general singly symmetric box section members. It does not have provisions for flange local buckling, web bend buckling and general yielding of welded box section beams. It also does not address box section beams with hybrid webs. This paper explains the development of design provisions for any general singly or doubly symmetric non-composite non-longitudinally stiffened, homogeneous or hybrid welded box section beam, covering all ranges of web and flange plate slenderness and addressing all relevant limit states. An extensive parametric study via test simulations was performed to evaluate the performance of the proposed equations. The finite element model was validated using existing experimental data and a good agreement, within 5% of experimental test results, was obtained. From the results of the parametric study, it was observed that for box section beams with compact or noncompact webs the cross section resistance is larger than yield moment and up to the plastic moment capacity of the effective cross section based on the effective width of the compression flange taking into account its post-buckling resistance. It was also found that for box section members the limit state of tension flange yielding is not required and the resistance is captured accurately by the general yielding strengths up to the plastic moment of the effective cross-section. The mean, median and standard deviation of the ratio of the beam strength from test simulations to the strength predicted by the proposed equations were 1.05, 1.04 and 0.06 respectively; thus showing that the proposed equations give a good prediction of the flexural resistance.

Ajinkya M. Lokhande and Donald W. White, Georgia Institute of Technology, Atlanta, GA

2017 Annual Stability Conference Presentation

Session SS1A- Technical Presentations: Stability of Thin-Walled Components and Assemblages
Tuesday, March 21, 2017
1:40 pm

Simulation of Conventional Cold-Formed Steel Sections Formed from Advanced High Strength Steel (AHSS)

The objective of this paper is to explore the potential impact of the use of advanced high strength steel (AHSS) to form traditional cold-formed steel structural members. To assess the impact of the adoption of AHSS on cold-formed steel member strength a group of forty standard structural lipped channel cross-sections are chosen from the Steel Framing Industry Association product list and simulated with AHSS material properties. The simulations consider compression with work on bending about the major axis in progress. Three different bracing conditions are employed so that the impact of local, distortional, and global buckling, including interactions can be explored. The simulations provide a direct means to assess the increase in strength created by the application of AHSS, while also allowing for future exploration of the increase in buckling mode interaction, imperfection sensitivity, and strain demands inherent in the larger capacities.

Hamid Foroughi and Benjamin W. Schafer, Johns Hopkins University, Baltimore, MD