Unified Steel Girder Design Specification. 2-1. Unified Straight and Curved. Steel
Girder Design Specifications. Introduction. Unified Steel Specifications. Straight.
Unified Straight and Curved Steel Girder Design Specifications
Introduction Unified Steel Specifications Straight Curved One Spec!
Unified Steel Girder Design Specification
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Unified Steel Girder Design ü Fundamentals ü Design Checks ü Examples
Fundamentals ü Primary-Strength Flexural & Shear Effects ü Lateral Flange Effects ü Differential Deflection Effects ü Torsion Effects ü Lateral Force Effects ü Second-Order Effects ü Cross Frame Forces
Unified Steel Girder Design Specification
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6.10.8 Flexural Resistance - Composite I FLB and LTB Flexure & Sections B a s i c F oinr m o f Negative All FLB & LTB Eqs Noncomposite I Sections - (cont’d) F n or M
Fm a x or M M max max
Fy r L − Lp b Fnc = Cb 1 − 1 − RhFy c Lr − L p
Anchor point 1
n
Fnc =RbRhFyc
Fyr Fnc = 1 − 1 − R Fyc h
λ f − λpf λrf − λpf
Rb RhFy c ≤ RbR hFy c
R bR hFyc
Anchor point 2 F r or M Mr r
compact
Fnc = Fcr ≤ RbRhFyc
noncompact
Lb r t
(inelastic buckling) nonslender
C bR b π 2 E
slender
2
(elastic buckling) L p oλ r pλ p f
L r λo rr λ rf
L b or b
fc /
2 tf c
Post Web Buckling Strength f bu ≤ φ f F yf ⇒ f bu ≤ φ f R b R h F yf Rb R h Buckled Web Sheds Stress to the Compression Flange Reducing Flange Yielding Moment
Dc
Tension Flange
Rb =
Moment First Yield with Buckled Web ≤ 1.0 M y = Fy S
2 Dc awc − λ rw ≤ 1.0 1200 + 300 awc tw
Rb = 1 −
Unified Steel Girder Design Specification
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Fundamentals ü Primary Flexural & Shear Effects ü Lateral Flange Effects ü Differential Deflection Effects ü Torsion Effects ü Lateral Force Effects ü Second-Order Effects ü Cross Frame Forces
Fundamentals ü Primary Flexural & Shear Effects ü Lateral Flange Effects ü Differential Deflection Effects ü Torsion Effects ü Lateral Force Effects ü Second-Order Effects ü Cross Frame Forces
Unified Steel Girder Design Specification
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Differential Load/Deflection Effects
• Outside girder carries more load • Vertical Deflection is not equal between adjacent girders => Torsional Effects on Girders, Lateral Flange Bending, and Affects fitup during construction
L1
OUTSIDE GIRDER
L2
PIER AB UT
UT AB
PLAN VIEW
INSIDE GIRDER
Fundamentals ü Primary Flexural & Shear Effects ü Lateral Flange Effects ü Differential Deflection Effects ü Torsion Effects ü Lateral Force Effects ü Second-Order Effects ü Cross Frame Forces
Unified Steel Girder Design Specification
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Torsion Effects
ü Deformations
ü Stresses
Torsion Deformations ü Twisting
ü Warping
=> Affect fit-up during construction
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6.7.2 Dead Load Camber l
Contract documents should state: • Intended erected position: • Webs vertical or plumb, or • Webs out-of-plumb
6.7.2 Dead Load Camber, cont’d l
Contract documents should state: • Condition for intended position: • No-load, • Steel dead load, or • Full dead load
Unified Steel Girder Design Specification
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Torsion Stresses • St. Venant • Warping l ta era L
g din n e eB g n Fla
Normal Stresses
XX Shear Stresses
Fundamentals ü Primary Flexural & Shear Effects ü Lateral Flange Effects ü Differential Deflection Effects ü Torsion Effects ü Lateral Force Effects ü Second-Order Effects ü Cross Frame Forces
Unified Steel Girder Design Specification
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Lateral Force Effects
f bu ± ? f l ≤ F r
f bu Bending stress due to vertical loads
fl
flange lateral bending stress due to wind, skew, or curvature
“One-Third” Rule 1.2
Fyf – fl / 3 (Hall and Yoo 1998)
1
0.856Fyf – fl / 3
fbu / Fyf
0.8
Flange Plastic Strength 0.6 0.4
0.7Fyf – fl / 3
0.2
AISC/AASHTO BeamColumn Interaction Curves
0 0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
f l / F yf
Unified Steel Girder Design Specification
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=> Lateral Force Effects & “One-Third” Rule
1 f l ≤ φ f Fnc 3 1 + f l ≤ φ f F yt 3
f bu + f bu
f bu Bending stress due to vertical loads
fl
flange lateral bending stress due to wind, skew, or curvature
f bu +
1 f l ≤ Fr 3
Mu +
1 f l S x ≤ M r Strength Limit State – Compact Straight 3
f bu + f l ≤ Fr
f bu +
Continuously Braced Flanges
Discretely Braced Flanges
Implementation of “One-Third” Rule
1 f l ≤ Fr 2
f bu ≤ F r
Unified Steel Girder Design Specification
Strength Limit State, Constructibility-Compression
1 ⇒1 3 1 1 Service Limit State ⇒ 3 2 Constructibility Yielding
ALL L.S., Continuously Braced Flanges, f l = 0
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f bu +
1 f l ≤ Fr 3
Mu +
1 f l S x ≤ M r Strength Limit State – Compact Straight 3
f bu + f l ≤ Fr
f bu +
Continuously Braced Flanges
Discretely Braced Flanges
Implementation of “One-Third” Rule
1 f l ≤ Fr 2
f bu ≤ F r
Strength Limit State, Constructibility-Compression
1 ⇒1 3 1 1 Service Limit State ⇒ 3 2 Constructibility Yielding
ALL L.S., Continuously Braced Flanges, f l = 0
f bu +
1 f l ≤ Fr 3
Mu +
1 f l S x ≤ M r Strength Limit State – Compact Straight 3
f bu + f l ≤ Fr
f bu +
Continuously Braced Flanges
Discretely Braced Flanges
Implementation of “One-Third” Rule
1 f l ≤ Fr 2
f bu ≤ F r
Unified Steel Girder Design Specification
Strength Limit State, Constructibility-Compression
1 ⇒1 3 1 1 Service Limit State ⇒ 3 2 Constructibility Yielding
ALL L.S., Continuously Braced Flanges, f l = 0
2-11
f bu +
1 f l ≤ Fr 3
Mu +
1 f l S x ≤ M r Strength Limit State – Compact Straight 3
f bu + f l ≤ Fr
f bu +
Continuously Braced Flanges
Discretely Braced Flanges
Implementation of “One-Third” Rule
1 f l ≤ Fr 2
f bu ≤ F r
Strength Limit State, Constructibility-Compression
1 ⇒1 3 1 1 Service Limit State ⇒ 3 2 Constructibility Yielding
ALL L.S., Continuously Braced Flanges, f l = 0
f bu +
1 f l ≤ Fr 3
Mu +
1 f l S x ≤ M r Strength Limit State – Compact Straight 3
f bu + f l ≤ Fr
f bu +
Continuously Braced Flanges
Discretely Braced Flanges
Implementation of “One-Third” Rule
1 f l ≤ Fr 2
f bu ≤ F r
Unified Steel Girder Design Specification
Strength Limit State, Constructibility-Compression
1 ⇒1 3 1 1 Service Limit State ⇒ 3 2 Constructibility Yielding
ALL L.S., Continuously Braced Flanges, f l = 0
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Fundamentals ü Primary Flexural & Shear Effects ü Lateral Flange Effects ü Differential Deflection Effects ü Torsion Effects ü Lateral Force Effects ü Second-Order Effects ü Cross Frame Forces (Primary Members)
Second-Order Effects (Art. 6.10.1.6) l
If
Lb > 1. 2L p
Cb Rb fbu Fyc
Second-order compression-flange lateral bending stresses may be approximated by amplifying first-order value:
0.85 f ≥ f l1 fl = f bu l1 1 − F cr
Unified Steel Girder Design Specification
Fcr =
Cb Rbπ 2 E L b rt
2
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Fundamentals ü Primary Flexural & Shear Effects ü Lateral Flange Effects ü Differential Deflection Effects ü Torsion Effects ü Lateral Force Effects ü Second-Order Effects ü Cross Frame Forces (Primary Members)
Unified Curved Steel Girder Design ü Fundamentals ü Design Checks ü Examples
Unified Steel Girder Design Specification
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Design Checks
ü Constructibility ü Service Limit State ü Fatigue Limit State ü Strength Limit State
6.10.3.2 Constructibility - Flexure lDiscretely
braced compression flanges 1 f bu + f l ≤ φ f Fnc ( FLB or LTB , max = R h F yc ) 3 f bu + fl ≤ φ f Rh Fyc fbu ≤ φ f Fcrw
l
⇒ Fcrw =
Discretely braced tension flanges
0.9 Ek D tw
2
k=
9
( Dc D )2
( Rb = 1 .0 )
fbu + f l ≤ φ f Rh Fyt l
Continuously braced flanges fbu ≤ φ f Rh Fyf
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Design Checks
ü Constructibility ü Service Limit State ü Fatigue Limit State ü Strength Limit State
6.10.4.2 Service Limit State Permanent Deformations l
Composite:
f f ≤ 0 .95 Rh Fyf
(
f c ≤ Fcrw M − only
)
f f f + l ≤ 0.95 Rh F yf 2
l
Noncomposite:
ff +
f c ≤ Fcrw
Unified Steel Girder Design Specification
ff +
fl ≤ 0.80 Rh Fyf 2 fl ≤ 0.80 Rh Fyf 2
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Design Checks
ü Constructibility ü Service Limit State ü Fatigue Limit State ü Strength Limit State
6.10.5 Fatigue & Fracture Limit State Fatigue stress ranges due to major-axis plus lateral bending shall be investigated
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Design Checks
ü Constructibility ü Service Limit State ü Fatigue Limit State ü Strength Limit State
6.10.7 Flexural Resistance Composite Sections in Positive Flexure
+
l
6.10.7.2 Noncompact Sections • Compact sections are not permitted for horizontally curved girders. • Compression flanges
f b u ≤ φ f R b R h F yc • Tension flanges
fbu +
1 f l ≤ φ f R h F yt 3
• Ductility Requirements - Concrete Crushing Prior to Plastification of Steel Section
Unified Steel Girder Design Specification
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-
6.10.8 Flexural Resistance Composite Sections in Negative Flexure and Noncomposite Sections • Discretely braced compression flanges f bu +
•
1 f l ≤ φ f Fnc ( FLB or LTB , max = Rb Rh F yc ) 3
Discretely braced tension flanges f bu +
1 f l ≤ φ f Rh Fyt 3
• Continuously braced flanges f bu ≤ φ f Rh Fyf
Additional Provisions for “STRAIGHT” Girder Design
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Additional Provisions for “STRAIGHT” Girder Design ü Compact Sections in Positive Flexure - Appendix A ü Moment Redistribution - Appendix B
Appendix A -- Flexural Resistance Composite Sections in Negative Flexure & Noncomposite Sections w/ Compact or Noncompact Webs l
Discretely braced compression flanges Mu +
l
1 f l S xc ≤ φ f M nc 3
Discretely braced tension flanges Mu +
Unified Steel Girder Design Specification
1 f l S xt ≤ φ f R pt M 3
yt
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Additional Provisions for Straight Girder Design ü Compact Sections in Positive Flexure - Appendix A ü Moment Redistribution - Appendix B
Appendix B - Moment Redistribution from InteriorPier Sections in Continuous-Span Bridges l
Replaces traditional 10 percent redistribution rule
l
Service II load combination and Strength Limit State
l
Refined and simplified methods
d fine e R
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Unified Steel Girder Design ü Fundamentals ü Design Checks ü Examples
FHWA - NSBA
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NCHRP 12-52
TNDOT
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TNDOT
SUMMARY Unified Steel Specifications Straight Curved One Spec! Enough Said!
Unified Steel Girder Design Specification
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