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

2017 Annual Stability Conference Presentation

Session SS2A – Stability of Thin-Walled Columns
Tuesday, March 21, 2017
3:15 pm

Buckling and Collapse Behavior of Screw-Fastened, Built-Up Cold-Formed Steel Columns of Varying Cross-Section Size: Experimental Investigation

An ongoing experimental effort using built-up cold-formed steel (CFS) columns is discussed in this paper. The quantification of partially-composite action, determination of member end fixity, and observation of buckling and post-buckling behavior is presented. The cross-sectional shape studied is a common back-to-back, lipped channel section with two self-drilling screw fasteners connecting the webs of the individual sections along their length. Sixteen different cross-section sizes are chosen, where each section is tested with two web fastener layout types as determined via AISI S100 (2016) section I1.2. A total of 32 monotonic, concentric compression tests are completed, and results show a vast range of deformation behavior, with local-global interaction and flexural-torsional modes common in many of the sections. Also, the column end conditions are determined to be semi-rigid, but almost fully-fixed for all sections. Ongoing work includes nonlinear FEA modeling validated by test data and a new design approach using finite strip-based modeling and the Direct Strength Method.

David C. Fratamico and Benjamin W. Schafer, Johns Hopkins University, Baltimore, MD; Kim J.R. Rasmussen, University of Sydney, Sydney, NSW, Australia