Agenda

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Agenda Day 1
800 am 815 am Introductions and House
Keeping 815 am 845 am Session 1 Load Rating
Basics 845 am 930 am Session 2 Basic Load
Rating Calculations 930 am 945 am Break 945
am 1145 am Session 3 Example Load Rating
Concrete Slab Bridge 1145 am 1200
pm Questions 1200 pm 100 pm Lunch 100 pm
230 pm Session 4 Example Load Rating Steel
Beam Bridges 230 pm 245 pm Break 245 pm
345 pm Session 4 Example Load Rating Steel
Beam Bridges (Cont) 345 pm 400 pm Questions
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Section Loss on Steel Beams

• Field measure section loss on steel beams.
• Section loss reduces the capacity of steel beams.
• The location of section loss on the beam is
  important
• Location on the beam (web flanges)
• Location along the length of the beam
• Capacity and Loads (DL LL) must be calculated
  at the same location

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• Example calculation with Section Loss
• Exterior beam example calculation
• Single span W33x130
• Built in 1968
• Fy 33,000 psi
• Original Section per AISC Manual

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• Estimated Section Loss
• Located 20 ft. from
• Centerline Bearing
• Step 1
• Calculate Capacity of
• Beam with section loss.

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• Establish Approximate Section
• Dimensions for Load Rating Calculations
• Use Section Loss Estimates
• and Field Measurements

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• Check for compact compression flange (top flange)
  

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• Check for compact web

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• Find distance from bottom of section to the
  Plastic Axis
• Recall that the plastic axis divides the top and
  bottom half areas of the section.

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• Find centroid of top half section from the
  Plastic Axis

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• Find centroid of bottom half section from the
  Plastic Axis

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• Calculate Plastic Section Modulus (Z)

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• Calculate Capacity

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• What if the section does not qualify as compact?
• Use the Elastic Section Modulus (S)
• instead of the Plastic Section Modulus (Z).

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• Find the Neutral Axis, Moment of Inertia (I), and
  Section Modulus (S)

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• Calculate Capacity (assuming non-compact)

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Questions ? ? ? ?
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Timber Decks on Steel Beams

• Timber deck does not supply continuous support to
  the compression flange of the steel beam
• Compression flange of the steel beams is braced
  only at the diaphragms/crossframes.

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Capacity of Beam w/ Timber Deck

• Beams will be one of the following
• Compact
• Braced Noncompact
• Partially Braced Noncompact
• Follow flowchart to determine beam capacity

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Flowchart to Determine Capacity of Steel Beams on
Timber Deck

• Check for Compactness check 3 equations
• Equation 10-93
• Equation 10-94
• Equation 10-96

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Flowchart to Determine Capacity of Steel Beams on
Timber Deck
If all three equations are satisfied then beam
is compact and Mu Fy Z If all three
equations are Not satisfied then check for braced
Noncompact.
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Flowchart to Determine Capacity of Steel Beams on
Timber Deck

• Check three equations for Braced Noncompact
• Equation 10-100
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• 2 Web thickness not less than D/150
• tw gt D/150
• Equation 10-101
• Lb

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Flowchart to Determine Capacity of Steel Beams on
Timber Deck

If all three equations are satisfied then beam is
braced noncompact and Mu equals the lesser of
1. Mu Fy Sxt 2. Mu Fcr Sxc
Rb Sxt Fcr Sxc Rb are defined in AASHTO
Section 10.48.2
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Flowchart to Determine Capacity of Steel Beams on
Timber Deck

If all three equations are not satisfied then
beam is partially braced noncompact and Mu
equals Mu Mr Rb Rb is calculated
using equation 10-103b Mr is calculated using
one of the following equations based on the
unsupported length Equations 10-103c,
10-103d, 10-103e, 10-103g
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Example Steel Beam Timber Deck
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Example Data

1. Beam spacing 3.0 ft.
2. Diaphragm spacing 5.0 ft.
3. Timber Deck 3 x 6 planks
4. Beam size W21 x 62
5. Fy 50,000 psi
6. Span length 50.0 ft.

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Questions ? ? ? ?