Unified LFRD Steel Design Specification

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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

2-1

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

Unified Steel Girder Design Specification

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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

2-13

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

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

6.10.4.2 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

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

6.10.7 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

Unified Steel Girder Design Specification

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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

Unified Steel Girder Design Specification

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Unified Steel Girder Design ü Fundamentals ü Design Checks ü Examples

FHWA - NSBA

Unified Steel Girder Design Specification

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NCHRP 12-52

TNDOT

Unified Steel Girder Design Specification

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TNDOT

SUMMARY Unified Steel Specifications Straight Curved One Spec! Enough Said!

Unified Steel Girder Design Specification

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