Design of Combined Bending and Compression Members in Steel - PowerPoint PPT Presentation

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Design of Combined Bending and Compression Members in Steel

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Design of Combined Bending and Compression Members in Steel Combined stresses Multi-story steel rigid frame Vierendeel steel truss cycle bridge Beaufort Reach ... – PowerPoint PPT presentation

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Title: Design of Combined Bending and Compression Members in Steel


1
Design of Combined Bending and Compression
Members in Steel
2
Combined stresses
Bi-axial bending
Bending and compression
3
  • Multi-story steel rigid frame

4
  • Rigid frames, utilizing moment connections, are
    well suited for specific types of buildings where
    diagonal bracing is not feasible or does not fit
    the architectural design
  • Rigid frames generally cost more than braced
    frames (AISC 2002)

5
  • Vierendeel steel truss cycle bridge Beaufort
    Reach, Swansea

6
  • Typical crane columns

7
fmax fa fbx fby lt fdes
( Pf / A ) ( Mfx / Sx ) ( Mfy / Sy ) lt fdes
(Pf / Afdes) (Mfx / Sxfdes) (Mfy / Syfdes)
lt 1.0
(Pf / Pr) (Mfx / Mr) ( Mfy / Mr) lt 1.0
8
Cross-sectional strength
Pf/Pr
1.0
1.0
Mf/Mr
9
Slender beam-columns
  • What if column buckling can occur ?
  • What if lateral-torsional buckling under bending
    can occur ?

Use the appropriate axial resistance and moment
resistance values in the interaction equation
10
Beam-column in a heavy industrial setting
BMD
11
Moment amplification
PE Euler load
12
Interaction equation
Axial load
Bending about y-axis
Bending about x-axis
?1 moment gradient factor (see next slide)
13
Moment gradient factor for steel columns with end
moments
M1
?1 0.6 0.4(M1/M2) 0.4 i.e. when moments
are equal and cause a single curvature, then ?1
1.0 and when they are equal and cause an
s-shape, then ?1 0.4
M2
14
Steel frame to resist earthquake forces
Warehouse building, Los Angeles
15
Moment gradient factor for other cases
v
?1 1.0
?1 0.85
?1 1.0
?1 0.6
?1 0.4
16
Design of steel beam-columns
  • Laterally supported
  • Cross-sectional strength
  • Supported in the y-direction
  • Overall member strength
  • Use moment amplification factor
  • Use buckling strength about x-axis (Crx)
  • Laterally unsupported
  • Buckling about y-axis (Cry)
  • Lateral torsional buckling (Mrx)
  • Use moment amplification factors
  • Usually the most critical condition
  • Note Mry never includes lateral-torsional
    buckling

17
Example of different support conditions
This column unsupported
These two columns supported in y-direction by
side wall
x direction
y direction
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