Page 63 - Modern Steel Construction (April 2019)

news & events

ENGINEERING JOURNAL
Second Quarter 2019 EJ Now Available

The second quarter 2019 issue of AISC’s bination with corresponding parts of the the flexural demands transmitted to col-
Engineering Journal is now available. You AISC Steel Construction Manual, provides umns (via braced frame beams) and (3) the
can access the current issue as well as past fairly good guidance on what is required to combinatorial effects of demands in biaxi-
issues at www.aisc.org/ej. Below is a sum- design Specification-compliant welds. How- ally loaded columns generated by orthogo-
mary of this issue, which includes articles ever, there seems to be some confusion nal ground-motion components.
on torsional design, welded connection and controversy in regard to a few of these
considerations, Chevron-configured spe- considerations, specifically: (1) When is the Steel Structures Research Update:
cial concentrically braced frames and steel load path from the weld to the connecting Steel Diaphragm Innovation Initiative
diaphragm research. The various AISC element(s) unclear? (2) When should the Judy Liu
publications mentioned are all accessible at ductility factor be applied to a weld? (3) The Steel Diaphragm Innovation Initia-
www.aisc.org/specifications. When should a weld be sized to develop tive (SDII) is a multiyear academic-industry
the strength of a connecting plate? partnership to advance the seismic perfor-
Torsion of Rectangular Connection mance of steel floor and roof diaphragms
Elements Probabilistic Assessment of Seismic in steel buildings. The team includes AISC
Bo Dowswell Force Demands in Biaxially Loaded T.R. Higgins and Milek Fellowship Award
Traditionally, the torsional design of Columns in Chevron-Configured winners for topics ranging from develop-
rectangular members has been based on Special Concentrically Braced Frames ments in long-span composite slabs to buck-
elastic calculations. For member design, Henry V. Burton, Nilofar Doorandish and ling-restrained braced frames (BRBFs) to
this approach is justified because beams Thomas Sabol continuity plate detailing for steel moment-
subjected to torsion are usually controlled Special concentrically braced frame resisting connections. The motivations for
by torsional rotation serviceability limits. (SCBF) columns are designed as force- creating SDII stemmed from issues with
However, designs that are based on a first controlled elements and are intended to respect to the knowledge base for steel dia-
yield criterion underestimate the strength respond elastically during moderate-to- phragm performance, codes and standards
of connection elements. To evaluate the high return-period events. When placed and missed opportunities for advancements
true torsional behavior of connection ele- at the intersection of orthogonal chev- in seismic performance-based design. Avail-
ments, various factors affecting the torsional ron-configured braced frames with fixed able research on steel diaphragms primarily
strength of short rectangular members are beam-column connections, SCBF columns focused on the strength of isolated systems;
investigated, showing that the torsional are subjected to biaxial loading, including little was known about ductility or whole-
strength of connection elements can be pre- flexural demands developed in the beams building performance. The team developed
dicted with rational analysis models using an due to unbalanced tension-compression a five-year plan to “advance the seismic per-
ultimate strength approach. brace forces. A probabilistic assessment of formance of steel floor and roof diaphragms
the force demands in biaxially and uniaxi- utilized in steel buildings through bet-
Guidance on Shear Rupture, ally loaded columns in chevron-configured ter understanding of diaphragm-structure
Ductility and Element Capacity in SCBF is presented herein. Nonlinear interaction, new design approaches and new
Welded Connections response history analyses are performed on 3D modeling tools that provide enhanced
Patrick J. Fortney, Larry S. Muir and 3D models of 3-, 9- and 20-story SCBFs, capabilities to designers utilizing steel dia-
William A. Thornton and statistical descriptions of the results are phragms in their building systems.”
Several considerations need to be made used to investigate (1) the force demands For more on this research update, see
while in the process of designing welds relative to the capacity-design-based and “Dedicated to Diaphragms” in the spe-
and welded connections. For the most elastic designs suggested by the AISC Seis- cial NASCC: The Steel Conference issue
part, the AISC Specification for Structural mic Provisions for Structural Steel Buildings of Modern Steel Construction, available at
Steel Buildings (ANSI/AISC 360), in com- (ANSI/AISC 341), (2) the implications of www.modernsteel.com.

STANDARDS
New AISC Seismic Standard now Available for Public Review

The current draft of a new AISC used with ASCE/SEI 41, which focuses (for a $35 charge) by calling 312.670.5411.
standard, Seismic Provisions for Evaluation on seismic evaluation and retrofit of Please submit comments, using the review
and Retrofit of Existing Structural Steel existing structural steel buildings. form, to Cynthia J. Duncan, AISC’s director
Buildings (AISC 342), is available for The standard and review form are both of engineering (duncan@aisc.org), by May
public review until May 1, 2019. The available for download at www.aisc.org/ 1, 2019 for consideration.
standard will provide provisions to be publicreview. Copies are also available

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