Structural Steel Beams: Plastic Moduli and Orientation
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Questions and Answers

Why do beams used to support concrete building and bridge floors often require lateral support?

  • To prevent buckling of the compression flange (correct)
  • To reduce the beam's self-weight
  • To resist shear forces
  • To increase the beam's moment of inertia

    • What is the primary reason why the compression flange of a beam may buckle?

  • Due to the type of material used
  • Due to the lack of lateral support (correct)
  • Due to the weight of the beam itself
  • Due to the type of loading conditions

    • What happens when the compression flange of a beam is long enough and slender enough?

  • It remains unaffected by its length and slenderness
  • It becomes weaker and more prone to buckling (correct)
  • It always buckles, regardless of lateral support
  • It becomes stronger and more resistant to buckling

    • What is the effect of residual stresses in a beam section on its buckling behavior?

    <p>It decreases the beam's resistance to buckling</p> Signup and view all the answers

    What is the primary purpose of lateral support in a beam?

    <p>To prevent buckling of the compression flange</p> Signup and view all the answers

    How does the tension in the other flange of a beam affect its buckling behavior?

    <p>It helps to restrain the compression flange from buckling</p> Signup and view all the answers

    What happens as the bending moment in a beam is increased?

    <p>The tendency of the compression flange to buckle becomes more pronounced</p> Signup and view all the answers

    What is a key factor affecting the amount of stress that causes buckling in the compression flange of a beam?

    <p>All of the above, as well as other factors</p> Signup and view all the answers

    What is the orientation of the beams in their upright positions?

    <p>About the horizontal axes</p> Signup and view all the answers

    Where can the proper plastic modulus about the y-axis be found for a beam turned on its side?

    <p>Table 3-4 of the Manual</p> Signup and view all the answers

    What percentage of strength does a W shape turned on its side retain compared to its upright position when subjected to gravity loads?

    <p>10-30%</p> Signup and view all the answers

    What type of loads are considered when analyzing the strength of a beam turned on its side?

    <p>Gravity loads</p> Signup and view all the answers

    What is the purpose of finding the proper plastic modulus about the y-axis for a beam turned on its side?

    <p>To determine the beam's strength under gravity loads</p> Signup and view all the answers

    What is the effect of turning a W shape on its side on its strength?

    <p>It decreases its strength</p> Signup and view all the answers

    What is the primary consideration when designing beams for moments?

    <p>The beam's strength under gravity loads</p> Signup and view all the answers

    Where can the tables giving dimensions and properties of shapes be found?

    <p>Part 1 of the AISC Manual</p> Signup and view all the answers

    What does the letter E represent in the classification of filler metal electrodes for shielded arc welding?

    <p>Electrode</p> Signup and view all the answers

    What is the minimum tensile strength of a weld indicated by the digits 70 in the classification E70XX?

    <p>70 ksi</p> Signup and view all the answers

    For what range of Fy values are E70 electrodes typically used?

    <p>36 ksi ≤ Fy ≤ 60 ksi</p> Signup and view all the answers

    What is the minimum length of a fillet weld in relation to the nominal leg size of the weld?

    <p>Four times the nominal leg size</p> Signup and view all the answers

    What is the maximum size of a fillet weld along edges of material less than 1/4 in thick?

    <p>The material thickness</p> Signup and view all the answers

    Why is it desirable to keep the weld back at least 1/16 in from the edge of a plate with a thickness of 1/4 in or more?

    <p>To ensure the inspector can clearly see the edge of the plate</p> Signup and view all the answers

    What happens if the length of a fillet weld is less than four times the nominal leg size of the weld?

    <p>The weld size is reduced to one-quarter of the weld length</p> Signup and view all the answers

    Where can provisions applying to welding be found?

    <p>Section J2.2b of the LRFD Specification</p> Signup and view all the answers

    What is the design strength of the connection shown in Figure, if the plates consist of A572 Grade 50 steel and E70 electrodes were used, and the 7/16-in fillet welds were made by the SMAW process?

    <p>50 ksi</p> Signup and view all the answers

    What is the minimum required strength of the electrodes to be used in the SMAW process for welding A572 Grade 50 steel?

    <p>70 ksi</p> Signup and view all the answers

    What is the purpose of using E70 electrodes in the SMAW process?

    <p>To increase the strength of the weld</p> Signup and view all the answers

    What is the minimum required thickness of the fillet welds to be used in the SMAW process for welding A572 Grade 50 steel?

    <p>5/16 in</p> Signup and view all the answers

    What is the design strength of the 5/16-in E70 fillet welds shown in the Figure?

    <p>50 ksi</p> Signup and view all the answers

    What is the purpose of using longitudinal and transverse fillet welds in the design of connections?

    <p>To increase the strength of the weld</p> Signup and view all the answers

    What is the LRFD design strength of the connection shown in Figure, if the plates consist of A572 Grade 50 steel and E70 electrodes were used, and the 5/16-in fillet welds were made by the SMAW process?

    <p>50 ksi</p> Signup and view all the answers

    What is the total LRFD design strength of the 5/16-in E70 fillet welds shown in the Figure?

    <p>80 ksi</p> Signup and view all the answers

    What is the primary purpose of welding in structural steel design?

    <p>To connect metallic parts by heating their surfaces to a plastic or fluid state</p> Signup and view all the answers

    What is the term for the type of beam section that is being discussed in the content?

    <p>Noncompact section</p> Signup and view all the answers

    What is the significance of the equation ϭϯ͘ϭϱ ƐŚŽǁƐ Ă ŚĂŶŐĞƌͲƚLJƉĞ?

    <p>It is a formula for determining the moment capacity of a section</p> Signup and view all the answers

    What is the main topic of the lecture in which the content is presented?

    <p>Welded Connections</p> Signup and view all the answers

    What is the name of the department that is presenting the lecture?

    <p>Civil Engineering Department</p> Signup and view all the answers

    What is the process by which metallic parts are connected in welding?

    <p>By heating their surfaces to a plastic or fluid state</p> Signup and view all the answers

    What is the term for the type of failure that is being discussed in the content?

    <p>Bending failure</p> Signup and view all the answers

    What is the purpose of the equations and formulas presented in the content?

    <p>To determine the structural integrity of the beam</p> Signup and view all the answers

    Study Notes

    Design of Beams for Moments

    • A beam's plastic modulus values in the table are given for beams in their upright positions.
    • If a beam is turned on its side, the proper plastic modulus about the y-axis can be found in Table 3-4 of the Manual or in the tables giving dimensions and properties of shapes in Part 1 of the AISC Manual.
    • A W shape turned on its side may be only 10 to 30 percent as strong as one in the upright position when subjected to gravity loads.

    Lateral Support of Beams

    • Beams used to support concrete building and bridge floors are often incorporated in these concrete floors, and will fall into Zone 1.
    • If the compression flange of a beam is without lateral support for some distance, it will have a stress situation similar to that existing in columns.
    • The compression flange of a beam may buckle unless lateral support is provided, and the amount of stress that will cause buckling is affected by many factors.

    Welded Connections

    • Welding is a process by which metallic parts are connected by heating their surfaces to a plastic or fluid state and allowing the parts to flow together and join (with or without the addition of other molten metal).
    • The filler metal electrodes for shielded arc welding are listed as E60XX, E70XX, etc., and the first set of digits indicates the minimum tensile strength of the weld in ksi.
    • E70 electrodes are used for steels with Fy values from 36 to 60 ksi, while E80 is used when Fy is 65 ksi.

    Welded Connections (continued)

    • The minimum length of a fillet weld may not be less than four times the nominal leg size of the weld.
    • The maximum size of a fillet weld along edges of material less than 1/4 in thick equals the material thickness.
    • For a plate with a thickness of 1/4 in or more, it is desirable to keep the weld back at least 1/16 in from the edge so that the inspector can clearly see the edge of the plate.

    Example Welded Connections

    • Examples of designing welded connections, including calculating the design strength of connections and determining the total LRFD design strength of fillet welds.

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    Description

    This quiz covers the effect of orientation on the plastic modulus of steel beams and their resulting strength when subjected to gravity loads.

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