Unified Straight and Curved Steel Girder Design Specifications - - PDF document
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 Fundamentals Design Checks
Unified Steel Girder Design Specification 2-1
Unified Straight and Curved Steel Girder Design Specifications Introduction Unified Steel Specifications
Straight Curved One Spec!
Unified Steel Girder Design Specification 2-2
Unified Steel Girder Design
Fundamentals Design Checks Examples
Primary-Strength Flexural & Shear Effects Lateral Flange Effects Differential Deflection Effects Torsion Effects Lateral Force Effects Second-Order Effects Cross Frame Forces
Fundamentals
Unified Steel Girder Design Specification 2-3
6.10.8 Flexural Resistance - Composite I Sections in Negative Flexure & Noncomposite I Sections
B a s i c Fo 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 tfc L 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
yc h b cr nc
F R R F F ≤ =
yc h b ncF R R F =
yc h b pf rf pf f yc h yr ncF R R F R F 1 1 F λ − λ λ − λ − − = 2 t b 2 b b
r L E R C π
FLB and LTB
y c h b y c h b p r p b y c h y r b nc
F R R F R R L L L L F R F 1 1 C F ≤ − − − − =
Post Web Buckling Strength
Buckled Web Sheds Stress to the Compression Flange Reducing Flange Yielding Moment
Tension Flange
. 1 S F M Web Buckled with Yield First Moment R
y y b
≤ = =
Dc
2 1 1.0 1200 300
wc c rw b wc w
a D R a t
= − −λ ≤ +
yf f h b bu
F R R f φ ≤
yf h b f bu
F R R f φ ≤ ⇒
Unified Steel Girder Design Specification 2-4
Primary Flexural & Shear Effects Lateral Flange Effects Differential Deflection Effects Torsion Effects Lateral Force Effects Second-Order Effects Cross Frame Forces
Fundamentals Fundamentals
Primary Flexural & Shear Effects Lateral Flange Effects Differential Deflection Effects Torsion Effects Lateral Force Effects Second-Order Effects Cross Frame Forces
Unified Steel Girder Design Specification 2-5
more load
equal between adjacent girders => Torsional Effects on Girders, Lateral Flange Bending, and Affects fit- up during construction
Differential Load/Deflection Effects
L1 L2 OUTSIDE GIRDER ABUT PIER ABUT INSIDE GIRDER
PLAN VIEW
Fundamentals
Primary Flexural & Shear Effects Lateral Flange Effects Differential Deflection Effects Torsion Effects Lateral Force Effects Second-Order Effects Cross Frame Forces
Unified Steel Girder Design Specification 2-6
Torsion Effects
Deformations Stresses Twisting Warping => Affect fit-up during construction
Torsion Deformations
Unified Steel Girder Design Specification 2-7
6.7.2 Dead Load Camber
Contract documents
should state:
position:
plumb, or
Contract documents
should state:
position:
6.7.2 Dead Load Camber, cont’d
Unified Steel Girder Design Specification 2-8
Torsion Stresses
Normal Stresses Shear Stresses
L a t e r a l F l a n g e B e n d i n g
Fundamentals
Primary Flexural & Shear Effects Lateral Flange Effects Differential Deflection Effects Torsion Effects Lateral Force Effects Second-Order Effects Cross Frame Forces
Unified Steel Girder Design Specification 2-9
Lateral Force Effects
Bending stress due to vertical loads flange lateral bending stress due to wind, skew, or curvature
r bu
F f f ≤ ±
l
?
l
f
bu
f
0.2 0.4 0.6 0.8 1 1.2 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
fl / Fyf fbu / 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
Unified Steel Girder Design Specification 2-10
=> Lateral Force Effects & “One-Third” Rule
Bending stress due to vertical loads flange lateral bending stress due to wind, skew, or curvature
yt f bu nc f bu
F f f F f f φ φ ≤ + ≤ +
l l
3 1 3 1
l
f
bu
f
Implementation of “One-Third” Rule
r bu
F f f ≤ +
l
3 1
r x u
M S f M ≤ +
l
3 1
r bu
F f f ≤ +
l r bu
F f f ≤ +
l
2 1
r bu
F f ≤
ALL L.S., Continuously Braced Flanges, Service Limit State Strength Limit State, Constructibility-Compression Strength Limit State – Compact Straight
=
l
f 2 1 3 1 ⇒
Constructibility Yielding
1 3 1 ⇒
Discretely Braced Flanges Continuously Braced Flanges
Unified Steel Girder Design Specification 2-11
Implementation of “One-Third” Rule
r bu
F f f ≤ +
l
3 1
r x u
M S f M ≤ +
l
3 1
r bu
F f f ≤ +
l r bu
F f f ≤ +
l
2 1
r bu
F f ≤
ALL L.S., Continuously Braced Flanges, Service Limit State Strength Limit State, Constructibility-Compression Strength Limit State – Compact Straight
=
l
f 2 1 3 1 ⇒
Constructibility Yielding
1 3 1 ⇒
Discretely Braced Flanges Continuously Braced Flanges
Implementation of “One-Third” Rule
r bu
F f f ≤ +
l
3 1
r x u
M S f M ≤ +
l
3 1
r bu
F f f ≤ +
l r bu
F f f ≤ +
l
2 1
r bu
F f ≤
ALL L.S., Continuously Braced Flanges, Service Limit State Strength Limit State, Constructibility-Compression Strength Limit State – Compact Straight
=
l
f 2 1 3 1 ⇒
Constructibility Yielding
1 3 1 ⇒
Discretely Braced Flanges Continuously Braced Flanges
Unified Steel Girder Design Specification 2-12
Implementation of “One-Third” Rule
r bu
F f f ≤ +
l
3 1
r x u
M S f M ≤ +
l
3 1
r bu
F f f ≤ +
l r bu
F f f ≤ +
l
2 1
r bu
F f ≤
ALL L.S., Continuously Braced Flanges, Service Limit State Strength Limit State, Constructibility-Compression Strength Limit State – Compact Straight
=
l
f 2 1 3 1 ⇒
Constructibility Yielding
1 3 1 ⇒
Discretely Braced Flanges Continuously Braced Flanges
Implementation of “One-Third” Rule
r bu
F f f ≤ +
l
3 1
r x u
M S f M ≤ +
l
3 1
r bu
F f f ≤ +
l r bu
F f f ≤ +
l
2 1
r bu
F f ≤
ALL L.S., Continuously Braced Flanges, Service Limit State Strength Limit State, Constructibility-Compression Strength Limit State – Compact Straight
=
l
f 2 1 3 1 ⇒
Constructibility Yielding
1 3 1 ⇒
Discretely Braced Flanges Continuously Braced Flanges
Unified Steel Girder Design Specification 2-13
Fundamentals
Primary Flexural & Shear Effects Lateral Flange Effects Differential Deflection Effects Torsion Effects Lateral Force Effects Second-Order Effects Cross Frame Forces (Primary Members)
Second-Order Effects (Art. 6.10.1.6)
If
Second-order compression-flange lateral bending stresses may be approximated by amplifying first-order value:
yc bu b b p b
F f R C L L 2 . 1 >
1 1
1 85 .
l l l
f f F f f
cr bu
≥ − =
2 2
=
t b b b cr
r L E R C F π
Unified Steel Girder Design Specification 2-14
Primary Flexural & Shear Effects Lateral Flange Effects Differential Deflection Effects Torsion Effects Lateral Force Effects Second-Order Effects Cross Frame Forces (Primary Members)
Fundamentals Unified Curved Steel Girder Design
Fundamentals Design Checks Examples
Unified Steel Girder Design Specification 2-15
Constructibility Service Limit State Fatigue Limit State Strength Limit State
Design Checks 6.10.3.2 Constructibility - Flexure
Discretely braced compression flanges
) max , ( 3 1
yc h nc f bu
F R LTB
FLB F f f = ≤ + φ
l yf h f bu
F R f φ ≤
yt h f bu
F R f f φ ≤ +
l
yc h f bu
F R f f φ ≤ +
l crw f bu
F f φ ≤
2
9 . = ⇒
w crw
t D Ek F
( )2
9 D D k
c
=
Discretely braced tension flanges Continuously braced flanges
) . 1 ( =
b
R
Unified Steel Girder Design Specification 2-16
Constructibility Service Limit State Fatigue Limit State Strength Limit State
Design Checks 6.10.4.2 Service Limit State Permanent Deformations
Composite: Noncomposite:
yf h f
F R f f 95 . 2 ≤ +
l crw c
F f ≤
yf h f
F R f 95 . ≤
yf h f
F R f f 80 . 2 ≤ +
l yf h f
F R f f 80 . 2 ≤ +
l
( )
M F f
crw c −
≤
Unified Steel Girder Design Specification 2-17
Constructibility Service Limit State Fatigue Limit State Strength Limit State
Design Checks 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 2-18
Design Checks
Constructibility Service Limit State Fatigue Limit State Strength Limit State
6.10.7 Flexural Resistance Composite Sections in Positive Flexure
6.10.7.2 Noncompact Sections
girders.
Plastification of Steel Section
1 3
bu f h yt
f f R F + ≤ φ
l
b u f b h yc
f R R F ≤ φ
+
Unified Steel Girder Design Specification 2-19
6.10.8 Flexural Resistance Composite Sections in Negative Flexure and Noncomposite Sections
) max , ( 3 1
yc h b nc f bu
F R R LTB
FLB F f f = ≤ + φ
l yf h f bu
F R f φ ≤
yt h f bu
F R f f φ ≤ +
l
3 1
“STRAIGHT” Girder Design
Unified Steel Girder Design Specification 2-20
Compact Sections in Positive Flexure - Appendix A Moment Redistribution - Appendix B
Additional Provisions for “STRAIGHT” Girder Design
Discretely braced compression flanges Discretely braced tension flanges
nc f xc u
M S f M φ ≤ +
l
3 1
Appendix A -- Flexural Resistance - Composite Sections in Negative Flexure & Noncomposite Sections w/ Compact or Noncompact Webs
yt pt f xt u
M R S f M φ ≤ +
l
3 1
Unified Steel Girder Design Specification 2-21
Compact Sections in Positive Flexure - Appendix A Moment Redistribution - Appendix B
Additional Provisions for Straight Girder Design
Appendix B - Moment Redistribution from Interior- Pier Sections in Continuous-Span Bridges
Replaces traditional 10 percent redistribution rule Service II load combination and Strength Limit State Refined and simplified methods
R e f i n e d
Unified Steel Girder Design Specification 2-22
Unified Steel Girder Design
Fundamentals Design Checks Examples
FHWA - NSBA
Unified Steel Girder Design Specification 2-23
NCHRP 12-52 TNDOT
Unified Steel Girder Design Specification 2-24
TNDOT SUMMARY Unified Steel Specifications
Straight Curved One Spec! Enough Said!