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Architecture 324
Structures II
Composite Sections and Steel Beam Design
•Steel Beam Selection - ASD
•Composite Sections
•Analysis Method
University of Michigan, TCAUP Structures II Slide 2/21
Standard section shapes:
W – wide flangeS – american standard beamC – american standard channelL – angleWT or ST – structural TPipeStructural Tubing
Steel W-sections for beams and columns
University of Michigan, TCAUP Structures II Slide 3/21
Source: University of Michigan, Department of Architecture
Columns:
Closer to squareThicker web & flange
Beams:
Deeper sectionsFlange thicker than web
Steel W-sections for beams and columns
University of Michigan, TCAUP Structures II Slide 4/21
Source: University of Michigan, Department of Architecture
Source: University of Michigan, Department of Architecture
Columns:
Closer to squareThicker web & flange
Beams:
Deeper sectionsFlange thicker than web
Steel W-sections for beams and columns
University of Michigan, TCAUP Structures II Slide 5/21
• Using the flexure equation, – set fb=Fb and solve for S
• Choose a section based on S from the table (D-35 and D-36)
– Bold faced sections are lighter– F’y is the stress up to which the
section is compact (•• is ok for all grades of Fy)
b
bb
FMS
FSM
IMcf
University of Michigan, TCAUP Structures II Slide 7/21
Source: Structural Principles, I. Engel 1984
1. Find the Section Modulus for the given section from the tables (D-35 and D-36).
2. Determine the maximum moment equation.
Example – Load Analysis of Steel Beam
Find Load w in KLF
University of Michigan, TCAUP Structures II Slide 8/21
Source: University of Michigan, Department of Architecture
3. Using the flexure equation, fb=Fb, solve for the moment, M.
4. Using the maximum moment equation, solve for the distributed loading, w.
Example – Load Analysis cont.
W30x116
w = 1.28 KLF
University of Michigan, TCAUP Structures II Slide 9/21
Source: University of Michigan, Department of Architecture
1. Use the maximum moment equation, and solve for the moment, M.
2. Use the flexure equation to solve for Sx.
Design of Steel Beam
Example
University of Michigan, TCAUP Structures II Slide 10/21
Source: University of Michigan, Department of Architecture
3. Choose a section based on Sx from the table (D35 and D36).
4. Most economical section is: W16 x 40Sx = 64.7 in3
Design of Steel Beam
Example
University of Michigan, TCAUP Structures II Slide 11/21
Source: I. Engel, Structural Principles, 1984
5. Add member self load to M and recheck Fb (we skip this step here)
6. Check shear stress:
Allowable Stress
Fv = 0.40 Fy
Actual Stressfv=V/(twd)
fv ≤ Fv
Design of Steel Beam
Example
University of Michigan, TCAUP Structures II Slide 12/21
6. Check Deflections
calculate actual deflection
compare to code limits
if the actual deflection
exceeds the code limit
a stiffer section is needed
Design of Steel Beam
Example
University of Michigan, TCAUP Structures II Slide 1335
Source: Standard Building Code, 1991
Composite Design
Steel W section with concrete slab “attached” by shear studs.
The slab acts as a wider and thicker compression flange.
University of Michigan, TCAUP Structures II Slide 14/21
Source: University of Michigan, Department of ArchitectureSource: University of Michigan, Department of Architecture
Effective Flange WidthSlab on both sides:(Least of the three)• Total width: ¼ of the beam span• Overhang: 8 x slab thickness• Overhang: ½ the clear distance to next
beam (i.e. the web on center spacing)
Slab on one side:(Least of the three)• Total width: 1/12 of the beam span• Overhang: 6 x slab thickness• Overhang: ½ the clear distance to next
beam
University of Michigan, TCAUP Structures II Slide 15/21
Source: University of Michigan, Department of Architecture
Source: University of Michigan, Department of Architecture
Analysis Procedure
1. Define effective flange width2. Calculate n = Ec/Es3. Transform Concrete width = n bc
4. Calculate Transformed Itr do NOT include concrete in tension
5. If load is known, calculate stress
or
6. If finding maximum load use allowable stresses. The lesser M will determine which material controls the section.
trconc
trsteel
InMcf
IMcf
ncIFM
cIFM
trconcc
trsteels
University of Michigan, TCAUP Structures II Slide 16/21