Hwk#4.pdf - ECI 132 Structural Design Metallic Elements Student Instructor Dr Michele Barbato Homework#4 Compression Members Problem#1 Determine

Hwk#4.pdf - ECI 132 Structural Design Metallic Elements...

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ECI 132 - Structural Design: Metallic Elements Student: Instructor: Dr. Michele Barbato Homework #4 Compression Members Problem #1 Determine explicitly (i.e., without using the footnote given in the Manual) whether a W6x15 is slender or non-slender in compression for F y = 60 ksi (5 points). Problem #2 The frame shown in the figure below is unbraced. The web of each member is in the plane of the frame. Column AB is subjected to an axial service dead load D = 155 kips, and an axial service live load L = 460 kips. Assume K y = 1.0 (i.e., the effective length factor for the y-axis is equal to 1). a. Using LRFD, determine the design strength for axial load of column AB if all members are made of A992 steel ( 15 points ). b. Using ASD, determine the allowable axial load for column AB if all members are made of A572 grade 60 steel ( 20 points ). Hint 1: When computing K x , neglect the effect of the stiffness reduction factor τ b (i.e., assume τ b = 1) in the calculation of the node stiffness coefficients G. Hint 2: In part (a), F y = 50 ksi implies that Table 4-1 can be used to find the design strength. By contrast, Table 4-1 cannot be used for the A572 grade 60 steel of part (b).
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Problem #3 (Extra credit) Read carefully the journal paper entitled “Torsional and Constrained-Axis Flexural-Torsional Buckling Tables for Steel W-Shapes in Compression” (a PDF copy of which is attached to this homework assignment). Summarize the content of this article in 400 words or less in an MS Word document. Use your own words. Explain the problem at hand, the procedure adopted to solve it, and the practical use of the results presented by the authors. Submit you file on Canvas (15 points: 10 points for accuracy of the information and 5 points for quality of the presentation).
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ENGINEERING JOURNAL / FOURTH QUARTER / 2013 / 205 Di Liu, Ph.D. Candidate, Civil Engineering Department, University of Kentucky, Lexington, KY. E-mail: [email protected] Brad Davis, Assistant Professor, Civil Engineering Department, University of Kentucky, Lexington, KY (corresponding). E-mail: [email protected] Leigh Arber, Staff Engineer, American Institute of Steel Construction, Chicago, IL. E-mail: [email protected] Rafael Sabelli, Principal and Director of Seismic Design, Walter P Moore, San Francisco, CA. E-mail: [email protected] INTRODUCTION H ot-rolled W-shape members are subjected to compres- sive axial forces when used as columns, braces, struts or collectors. The available compressive strength—LRFD design strength or ASD allowable strength—per the AISC Specification (AISC, 2010) Chapter E is the minimum based on the limit states of flexural buckling (FB) and torsional buckling (TB; see Figure 1a). W-shape FB available strength calculations are facilitated by design aids in Part 4 of the AISC Steel Construction Manual (AISC, 2011), especially Tables 4-1 and 4-22. TB is not included in these design aids because when the weak-axis FB effective unbraced length, ( KL ) y , equals the TB effective unbraced length, K z L , TB only controls for very few cases, and in those cases only by a margin of less than 0.5%.
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