2017 Annual Stability Conference Presentation

Session SS2B – Technical Presentations: Stability at Elevated Temperatures
Tuesday, March 21, 2017
3:15 pm

Stability Analysis of Steel Columns under Cascading-Hazard of Earthquake and Fire

In this study, a nonlinear finite element formulation is developed and utilized to perform stability analysis of W-shape steel columns subjected to non-uniform longitudinal temperature profiles in the absence or presence of inter-story drift, representing residual drift following an earthquake. This formulation takes into account the residual stress distribution in steel hot-rolled W-shape sections, initial geometric imperfections in the steel columns, non-uniform longitudinal temperature distribution, and temperature-dependent material properties. The results indicate an excellent agreement with available strength design equations of steel columns at ambient and elevated temperatures. A set of equations is then proposed to predict the critical buckling stress in steel columns under fire and fire following earthquake considering residual drifts and non-uniform longitudinal temperature distributions. The proposed equations can be implemented to investigate the performance of steel structures under fire and fire following earthquake considering stability as engineering demand parameter.

Mehrdad Memari and Hussam Mahmoud, Colorado State University, Fort Collins, CO

2017 Annual Stability Conference Presentation

Session S9 – Stability of Shells
Thursday, March 23, 2017
4:15 pm

On the Investigation of the Most Critical Shape Imperfections for Wind Turbine Tower Shell Structures

Among the many technical goals of today’s wind energy industry is to develop solutions for taller wind turbine towers. The increase in height of wind turbine towers is imperative to achieve goals of efficiency and competitiveness, as the wind profile is stronger at higher heights. However, making higher wind turbine tower structures poses numerous challenges to structural engineers. One of the biggest challenges for thin cylindrical shells, such as tall wind turbine structures is their high sensitivity to geometric imperfections. It is expected that the capacity of this type of shells can drop significantly in the presence of geometric imperfections. This paper is studying this sensitivity by investigating the worst shape imperfection for a specific wind turbine tower geometry. For this investigation, the elastic modes of the structure are utilized either as individual shapes or as the basis for shape combinations, in order to find the worst initial geometric imperfection shape.

Kshitij Kumar Yadav and Simos Gerasimidis, University of Massachusetts, Amherst, MA;  Jens Lycke Wind, Vestas Wind Systems A/S, Aarhus, Denmark

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

2017 Annual Stability Conference Presentation

Session S4 – Stability of Beam-Columns
Wednesday, March 22, 2017
4:30 pm

Major and Minor Axis Stiffness Reduction of Steel Beam-Columns Under Axial Compression and Tension Conditions

This research focused on developing a deeper understanding of the stiffness reduction that occurs in W-Shapes due to yielding of the cross-section under uniaxial bending and axial loading conditions. A detailed fiber element model was used to develop three-dimensional m-p-t surface plots: (a) minor axis bending under axial compression; (b) major axis bending under axial compression; (c) minor axis bending under axial tension; and (d) major axis bending under axial tension. The m and p conditions around the perimeter of the 3D surfaces were studied in detail and analytical expressions are provided for each of the loading conditions at the initial yield and fully plastic conditions. The m-p-t surface plots were used as a basis to develop a nonlinear material model for practical use. The material model was used as normalized tangent modulus expressions in MASTAN2, and it was found to provide results that were in close agreement with published benchmark frame results. The material model is based on reasoning that is consistent with what is known about the effects of the residual stresses in W-shapes. It provides a straightforward approach for modeling the distributed plasticity when conducting a nonlinear analysis of planar steel frames with compact W-shapes. The material model can accommodate any W-shape and assumed maximum value of residual stress.

Barry T. Rosson, Florida Atlantic University, Boca Raton, FL

2017 Annual Stability Conference Presentation

Session S4 – Stability of Beam-Columns
Wednesday, March 22, 2017
4:30 pm

Comprehensive Stability Design of Steel Members and Systems via Inelastic Buckling Analysis – Beam-Column Validation Studies

This research provides an overview of a comprehensive approach for the design of structural steel members and systems via an Inelastic Nonlinear Buckling Analysis (INBA) that includes appropriate column, beam and beam-column inelastic stiffness reduction factors. The stiffness reduction factors are derived from the ANSI/AISC 360 Specification column, beam and beam-column strength provisions. The resulting procedure provides a relatively rigorous check of member design resistances accounting for continuity effects across braced points, as well as lateral and/or rotational restraint from other framing including a wide range of types and configurations of stability bracing. With this approach, no separate checking of the corresponding Specification member stability design resistance equations is required. The buckling analysis captures these resistances. In addition, no calculation of effective length (K) factors and moment gradient and/or load height (Cb) factors, is necessary. The buckling analysis directly captures the fundamental mechanical responses associated with these design strength factors. This approach is coupled with the AISC Direct Analysis Method (the DM), for calculation of the pre-buckling displacement effects, to fully satisfy the stability design requirements of the AISC Specification. In addition to explaining the method’s key concepts, the research focuses on validation of the method for capture of the lateral-torsional buckling response of general doubly-symmetric I-section beam-columns subjected to major-axis bending. Results from the recommended approach and from routine application of the DM are compared to the results from test simulation per Appendix 1.3 of the AISC Specification.

Oğuzhan Toğay and Donald W. White, Georgia Institute of Technology, Atlanta, GA

2017 Annual Stability Conference Presentation

Session SS1B – Technical Presentations: Special Topics in Structural Stability
Tuesday, March 21, 2017
1:40 pm

Rigging and Bracing Stability: Considerations For Moving, Lifting and Placing a Non-Building Structural Module

One of the large structural steel-plate wall modules in the AP1000 nuclear power plant makes up a significant part of the In-containment Refueling Water Storage Tank (IRWST). This outer circular portion of the tank consists of a stainless steel plate stiffened with structural sections in the vertical direction and angles in the horizontal direction. The stability issues associated with this open-walled structural module had to be addressed as it is being placed inside the Containment Building. More importantly, when this same structural module was rigged with a four-point lifting plan in China, its overall stability came into question. A new eight-point rigging, temporary structural braces, and lifting plan was created for the U.S. AP1000 plants that considered not only the stability of the structural module, but of the rigging members that would be employed in the lift and ultimately the placement of the module. Finite element analysis simulations of the lift were performed to evaluate the stresses and stability of the structural module and rigging including the new lifting locations and lug plate designs that were determined.

Michael Mudlock, Simpson Gumpertz & Heger, Inc., Houston, TX; Perry S. Green, Bechtel Power Corporation, Waynesboro, GA; Andrew Sarawit, Simpson Gumpertz & Heger, Inc., Waltham, MA; Francis J. Byrne, Westinghouse (WECTEC), Waynesboro, GA

Abstracts are now being accepted for the 2018 SSRC Annual Stability Conference, April 10-13, 2018 in Baltimore, MD. Researchers are encouraged to submit an abstract summarizing ongoing or recently completed research on stability of metal structures, or metal-concrete composite structures.

Please visit the Annual Stability Conference web page for more details.

2017 Annual Stability Conference Presentation

Session S3 – Advances in Stability Bracing
Wednesday, March 22, 2017
3:15 pm

Impact of Clip Connection and Insulation Thickness on Bracing of Purlins in Standing Seam Roof Systems

The flexural strength of purlins in standing seam roof systems is highly dependent upon the extent to which the sheathing provides lateral and torsional restraint.  For standing seam systems, the interface between the sheathing and purlin is bridged by a clip. For the sheathing to provide lateral restraint to the purlin, forces must be transferred over the height of the clip and the effects of this additional eccentricity is not well understood.  This paper reports the results of a series of 25 tests that quantify this eccentricity, referred to as effective standoff, for a representative sample of standing seam roof systems currently in use within the industry. The implications of this additional eccentricity on the bracing forces within a standing seam roof system are discussed.

Michael W. Seek and Daniel McLaughlin, Old Dominion University, Norfolk, VA