Unified Straight and Curved Steel Girder Design Specifications · 2008. 3. 5. · Unified Steel...

Unified Steel Girder Design Specification 2-1

Unified Straight and Curved Steel Girder Design Specifications

IntroductionUnified Steel Specifications

StraightCurved

One Spec!


Unified Steel Girder Design

ü Fundamentals

ü Design Checks

ü Examples

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

Fundamentals


6.10.8 Flexural Resistance - Composite I Sections in Negative Flexure & Noncomposite I Sections - (cont’d)B a s i c F o r m o f A l l F L B & L T B E q s

M m a x

M r

λ p λ r

c o m p a c t n o n c o m p a c t

n o n s l e n d e r s l e n d e r

( i n e l a s t i c b u c k l i n g )

( e l a s t i c b u c k l i n g )

M m a x

M r

λ p λ r

c o m p a c t n o n c o m p a c t

n o n s l e n d e r s l e n d e r

( i n e l a s t i c b u c k l i n g )

( e l a s t i c b u c k l i n g )

A n c h o r p o i n t 1

A n c h o r p o i n t 2

L b o r b fc / 2 tfcL p o r λ p f L r o r λ rf

F n o r M n

F m a x o r M m a x

F r o r M r

ychbcrnc FRRFF ≤=

ychbnc FRRF =ychb

pfrf

pff

ych

yrnc FRR

FR

F11F

λ−λλ−λ

−−=

2

t

b

2bb

rL

ERC

π

FLB and LTB

y chby chbpr

pb

y ch

y rbnc FRRFRR

LL

LL

FR

F11CF ≤

−

−

−−=

Post Web Buckling Strength

Buckled Web Sheds Stress to the Compression Flange Reducing Flange Yielding Moment

Tension Flange 0.1

SFMWeb Buckled withYield First Moment

Ryy

b ≤=

=

Dc

21 1.01200 300

wc crwb

wc w

a DRa t

= − − λ ≤+

yffhb

bu FRR

fφ≤ yfhbfbu FRRf φ≤⇒


ü Primary Flexural & Shear Effects



ü Torsion Effects




Fundamentals

Fundamentals




ü Torsion Effects





• Outside girder carries more load

• Vertical Deflection is not equal between adjacent girders

=> Torsional Effects on Girders, Lateral Flange Bending, and Affects fit-up during construction

Differential Load/Deflection Effects

L1 L2 OUTSIDEGIRDER

ABUT

PIER

ABUT

INSIDEGIRDER

PLAN VIEW

Fundamentals




ü Torsion Effects





Torsion Effects

ü Deformations

ü Stresses

ü Twisting

ü Warping

=> Affect fit-up during construction

Torsion Deformations


6.7.2 Dead Load Camber

l Contract documents should state:

• Intended erected position:

• Webs vertical or plumb, or

• Webs out-of-plumb

l Contract documents should state:

• Condition for intended position:

• No-load,• Steel dead load, or• Full dead load

6.7.2 Dead Load Camber, cont’d


• St. Venant

• Warping

Torsion Stresses

Normal Stresses Shear Stresses

X XLat

eral Fla

nge Bend

ing

Fundamentals




ü Torsion Effects





Lateral Force Effects

Bending stress due to vertical loads

flange lateral bending stress due to wind, skew, or

curvature

rbu Fff ≤± l?

lf

buf

0

0.2

0.4

0.6

0.8

1

1.2

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

fl / Fyf

f bu

/ Fyf Flange Plastic Strength

Fyf – fl / 3 (Hall and Yoo 1998)

AISC/AASHTO Beam-Column Interaction Curves

0.7Fyf – fl / 3

0.856Fyf – fl / 3

“One-Third” Rule


=> Lateral Force Effects & “One-Third” Rule

Bending stress due to vertical loads

flange lateral bending stress due to wind, skew, or

curvature

ytfbu

ncfbu

Fff

Fff

φ

φ

≤+

≤+

l

l

3131

lf

buf

Implementation of “One-Third” Rule

rbu Fff ≤+ l31

rxu MSfM ≤+ l31

rbu Fff ≤+ l

rbu Fff ≤+ l21

rbu Ff ≤ ALL L.S., Continuously Braced Flanges,

Service Limit State

Strength Limit State, Constructibility-Compression

Strength Limit State – Compact Straight

0=lf

21

31

⇒

Constructibility Yielding 131

⇒

Disc

rete

ly Br

aced

Fla

nges

Cont

inuo

usly

Brac

ed F

lang

es



rbu Fff ≤+ l31

rxu MSfM ≤+ l31

rbu Fff ≤+ l

rbu Fff ≤+ l21


Service Limit State



0=lf

21

31

⇒


⇒

Disc

rete

ly Br

aced

Fla

nges

Cont

inuo

usly

Brac

ed F

lang

es


rbu Fff ≤+ l31

rxu MSfM ≤+ l31

rbu Fff ≤+ l

rbu Fff ≤+ l21


Service Limit State



0=lf

21

31

⇒


⇒

Disc

rete

ly Br

aced

Fla

nges

Cont

inuo

usly

Brac

ed F

lang

es


Fundamentals




ü Torsion Effects



ü Cross Frame Forces (Primary Members)

Second-Order Effects (Art. 6.10.1.6)

l If

Second-order compression-flange lateral bending stresses may be approximated by amplifying first-order value:

ycbu

bbpb Ff

RCLL 2.1>

111

85.0lll ff

Ff

f

cr

bu≥

−=

2

2

=

t

b

bbcr

rL

ERCF

π





ü Torsion Effects



ü Cross Frame Forces (Primary Members)

Fundamentals

Unified Curved Steel Girder Design

ü Fundamentals

ü Design Checks

ü Examples


ü Constructibility

ü Service Limit State

ü Fatigue Limit State

ü Strength Limit State

Design Checks

6.10.3.2 Constructibility - FlexurelDiscretely braced compression flanges

)max,(31

ychncfbu FRLTBorFLBFff =≤+ φl

yfhfbu FRf φ≤

ythfbu FRff φ≤+ l

ychfbu FRff φ≤+ l

crwfbu Ff φ≤2

9.0

=⇒

w

crw

tD

EkF ( )2

9

DDk

c

=

l Discretely braced tension flanges

l Continuously braced flanges

)0.1( =bR


ü Constructibility




Design Checks

6.10.4.2 Service Limit State Permanent Deformations

l Composite:

l Noncomposite:

yfhf FRff 95.02

≤+ l

crwc Ff ≤

yfhf FRf 95.0≤

yfhf FRff 80.02

≤+ l

yfhf FRff 80.02

≤+ l

( )onlyMFf crwc−≤


ü Constructibility




Design Checks

6.10.5 Fatigue & Fracture Limit State

Fatigue stress ranges due to major-axis plus lateral bending shall be investigated


Design Checks

ü Constructibility




6.10.7 Flexural ResistanceComposite Sections in Positive Flexurel 6.10.7.2 Noncompact Sections

• Compact sections are not permitted for horizontally curved girders.

• Compression flanges

• Tension flanges

• Ductility Requirements - Concrete Crushing Prior to Plastification of Steel Section

13b u f h ytf f R F+ ≤ φl

b u f b h ycf R R F≤ φ

+


6.10.8 Flexural ResistanceComposite Sections in Negative Flexure

and Noncomposite Sections• Discretely braced compression flanges

• Discretely braced tension flanges

• Continuously braced flanges

)max,(31

ychbncfbu FRRLTBorFLBFff =≤+ φl

yfhfbu FRf φ≤

ythfbu FRff φ≤+ l31

-

Additional Provisions for

“STRAIGHT” Girder Design


ü Compact Sections in Positive Flexure - Appendix A

ü Moment Redistribution - Appendix B


“STRAIGHT” Girder Design

l Discretely braced compression flanges

l Discretely braced tension flanges

ncfxcu MSfM φ≤+ l31

Appendix A -- Flexural Resistance -Composite Sections in Negative Flexure &

Noncomposite Sections w/ Compact or Noncompact Webs

ytptfxtu MRSfM φ≤+ l31


ü Compact Sections in Positive Flexure - Appendix A

ü Moment Redistribution - Appendix B


Straight Girder Design

Appendix B - Moment Redistribution from Interior-Pier 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

Refined


Unified Steel Girder Design

ü Fundamentals

ü Design Checks

ü Examples

FHWA - NSBA


NCHRP 12-52

TNDOT


TNDOT

SUMMARYUnified Steel Specifications

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Unified Straight and Curved Steel Girder Design Specifications · 2008. 3. 5. · Unified Steel...

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