b'ENGINEERS CORNEROur Strength Is MoreThan Superior Products.CISC provides this column as part of its commitment to the education of those interested in the use of steel in construction. Neither CISC nor the author assumes responsibility for errors orBehind every joist and piece of deck we supply oversights resulting from the use of the information contained herein. Suggested solutions mayis a commitment to go beyond just providing not necessarily apply to a particular structure or application and are not intended to replace thehigh-quality products. We foster powerful expertise of a licensed professional engineer or architect. relationships that allow us to understand your business needs and partner with you to make Question1:WhatisthebucklingresistanceofaThis buckling mode is also referred to as constrained- sure your project outcomes are successful.compression member when only one flange is laterallyaxis torsional buckling in ANSI/AISC (2016). Due to the Charles Albert, P.Eng.braced?finite stiffness of the lateral bracing, it is recommendedWe understand you have choices when it Manager of Technicalto limit P eyzto 90% of the calculated value.comes to sourcing your deck and joists needs. Publications & Services, CISC In case (1), since the girts provide discrete rather than continuous bracing, flexural buckling of the columnVulcraft is committed to earning your trust and about the weak axis should also be checked separatelybusiness by delivering value in our products, using S16-14 Clause 13.3.1 with the unsupported lengthservices and relationships.taken as the girt spacing. Our plants are in full operation and eager to References: deliver results at every phase of your project.ANSI/AISC.2016.SpecificationforStructuralSteel Buildings.AmericanInstituteofSteelConstruction,So lets work together andChicago, Illinois. build something that lasts.Ziemian, R. D. 2010. Guide to Stability Design Criteria for FIGURE 1 Metal Structures, 6th Edition. John Wiley and SonsTorsional-Flexural Buckling About a Constrained AxisAnswer: Although this condition is not covered in CSAQuestion 2: How is the formula for M uin S16-14 Clause S16-14, it occurs mainly in two situations: (1) exterior13.6(e) applied to a WT-section in bending with the stemNucor, Vulcraft Canada, Inc.columns in single-storey buildings, and (2) beams inin compression? And what value ofxshould be used? 3307 Allard Ave.braced frames supporting a steel deck. In case (1), theLeduc, AB T9E 0Z5 587.453.0620outside flange of the column is laterally braced by girts while the inside flange is unsupported. In case (2), the topNucor, Vulcraft Canada, Inc. flange of a roof beam, for example, is continuously1362 Osprey Dr.bracedbythedeckwhilethebottomflangeisAncaster, ON L9G 4V5 unsupported. In both cases, torsional-flexural buckling289.443.2000under axial loading occurs about a constrained axis of twist located near the braced flange, as shown in Figure 1.Ziemian(2010)providesaformulafortheelastic buckling load: FIGURE 2Laterally Unsupported WT-SectionAnswer: The same formula for the elastic buckling moment,M u ,isusedwhethertheWTstemisin compression or tension. The only difference is that the asymmetry parameter,x , is taken to be (a) positive Questionsonvariouswhen the flange is in flexural compression, and (b) aspectsofdesignandwhere: negative otherwise (i.e. when the stem is in flexural constructionofsteela = Distance between the constrained axis and thecompression), as shown in Figure 2. In case (b), the buildings and bridges areshear centre of the memberWT-section is less stable, and M uwill therefore be welcome.TheymaybeG = Shear modulus smaller than in case (a).submittedviaemailtoh = Distance between the flange centroids The values of x listed in Part 6 of the Handbook of info@cisc-icca.ca.CISCI y= Weak-axis moment of inertia Steel Construction were calculated for WT-sections receives and attends to aJ = St. Venant torsional constant usingtheexactexpressiongiveninPart2(CISC large volume of inquiries;L y= Unsupported member length between points ofCommentary on CSA S16-14). The formula forx in onlyaselectedfewarezero twist Clause 13.6(e), on the other hand, is an approximationVULCRAFT CANADApublished in this column. P ey= Euler (flexural) buckling load about the weak axis forsingly-symmetricbeamsthatisnotvalidfor r x, r y=Principal radii of gyration T-sections (according to the new CSA S16-19). AS Powerful Partnerships. Powerful Results.8|WINTER 2020 ADVANTAGE STEEL'