Module 1 – Outlineo LRFD Bridge Seismic Design Requirementso ABC Seismic Research and Implementation o Innovations in Bridge Seismic Designo Seismic Design Requirements and Design Examples

1. Khashayar Nikzad, Principal Engineer, Trantech

2. Bijan Khaleghi, State Bridge Design Engineer - WSDOT

Module 1 – Latest Seismic ABC Applications

FIU – UTC: In-Depth Web Training September 10, 2019: 11:00 am (EST)

Latest Seismic ABC Applications

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Accelerated Bridge Construction - Seismic

Emulative Constructiono No new concepts to prove.o Easier acceptance: “performs just like c.i.p.”o Use of precast shortens construction time

Innovative Connection Typeso Socket and Pocket connectionso Super-Elastic Materialso Self-Centering

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Connections need to be:• Constructible • Seismic Resilient• Long term Performance & Longevity

LRFD Bridge Design Specifications Bridges shall be designed for specified limit states to achieve the objectives of constructability, safety, and serviceability, with due regard to issues of inspectability, economy, and aesthetics.

Guide Specifications for LRFD Seismic Bridge DesignThe LRFD Guide Specifications apply to the design and construction of conventional bridges to resist the effects of earthquake motions.

LRFD Bridge Seismic and ABC Design Specifications

LRFD Guide Specifications for Accelerated Bridge ConstructionThe provisions are for common prefabricated elements and systems for Accelerated Bridge Construction (ABC) projects.The provisions shall be used in conjunction with the AASHTO LRFD Bridge Design Specifications.

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Seismic Hazard Consideration• Cascadia Subduction Zone• M9 Subduction Mega EQ• Basin Effect

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Examples of Bridge Earthquake Damages5

Use of ERS and ERE to ensure required seismic performance• Permissible• Permissible with Approval• Not Recommended for New Bridge

LRFD SGS: Bridge System ERS and ERE Categories6

Recommended Duct Size & Embedment Length – ABC

Bar

fy

fu

7Type 1: Ductile Substructure with Essentially Elastic Superstructure. EQ

PlasticHinge

Column Confinement and Performance Curves

Ductility Performance Curves for Reinforced Concrete Columns in SDCs B, C, and D

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LRFD SGS Capacity Design For Caps for Longitudinal Direction

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Capacity Design Requirement for SDCs B, C and Do Capacity-protected members are designed to remain essentially

elastic when the plastic hinge reaches its overstrength moment capacity, Mpo = 1.25 times the moment demand

o Moment-resisting joints is proportioned so that the principal stresses satisfy the requirements below.

P-Δ effects Requirement: May be ignored in the analysis and design if:

prdl MP 250.≤∆

nrdl MP 25.0≤∆

• For reinforced concrete columns:

• For steel columns:

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Maximum axial load acting on a column: Pu < 0.2 fc’Ag

Considerations for Seismic Resiliency for ABC

Balanced Stiffness Concept for Frames, Bents and Columnso Between any two bents within a frame or between any two columns

within a bento Between adjacent bents within a frame or between adjacent columns

within a bento Balanced Frame Geometry - (ratio of fundamental periods of

vibration)

0.50 m xK

m xK

iej

jei ≥ 0.75

m xK

m xK

iej

jei ≥0.7

TT

j

i ≥

Type 3: Elastic Superstructure and Substructure with a Fusing Mechanism Between The Two

o Durability & Long-term Performance of Bearings

o Expansion joints to accommodate seismic movements for bearings to function properly.

o Adequate clearance for the seismic displacement between the girders and abutment back wall.

o Bearings type Combinations not allowed.

EQSeismicIsolation

11AASHTO SGS Seismic Design Strategies

WSDOT Post EQ Functionality and Serviceability Requirements

Bridge Operational Importance Category

Seismic Hazard Evaluation Level

Expected Post Earthquake Damage State

Expected Post Earthquake Service Level

Normal SEE Significant No ServiceEssential SEE Moderate Limited Service

FEE Minimal Full ServiceCritical SEE Minimal to Moderate Limited Service

FEE None to Minimal Full Service

Seismic Critical Member

Displacement Ductility Demand Limits

Normal

Bridges

Essential Bridges Critical Bridges

SEE FEE SEE FEE

Wall Type Pier in Weak Direction 5.0 2.5 1.5 1.5 1.0

Wall Type Pier in Strong Direction 1.0 1.0 1.0 1.0 1.0

Single Column Bent 5.0 2.5 1.5 1.5 1.0

Multiple Column Bent 6.0 3.5 2.0 1.5 1.0

Pile/Shaft-Column with Plastic Hinge at Top of Column 5.0 3.5 2.0 1.5 1.0

Pile/Shaft-Column with Plastic Hinge Below Ground 4.0 2.5 1.5 1.5 1.0

Superstructure 1.0 1.0 1.0 1.0 1.0

Displacement Ductility Demand Values, μD

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Seismic Resiliency with use of Innovative Designs, Materials, and construction:o Use of super-elastic materials in columnso Use of prestressing in columnso Other innovative designs

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Other Options: Innovative Designs for Seismic Resiliency

Other Options: Self Centering Piers using Super Elastic Materials for Bridge Columns

Shape Memory Alloy ( SMA )Engineered Cementitious Composite ( ECC ) Three - 0.4 Scale Columns (2 SMA/ECC, 1 RC)

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Other Options: Seismic Resiliency with PT Self Centering

30-50% fpu

(a) (b) (c)

Figure: Schematics of the proposed system: (a) column typical cross-section; (b) bent components and rocking kinematics; and (c) joint rotation.

Self-Centering Precast Concrete Dual-Steel-Shell Columns for Accelerated Bridge Construction

Hysteretic response: (a) conventional ductile system; (b) purely rocking system; and (c) hybrid rocking system.

Other Options: Dual Shell CFST Self-Centering Capability - ABC

UCSD: ABC – Self Centering

ABC-UTC: UHPC Connection for Seismic Performance Self-Centering Capability - ABC

UHPCUHPC

FIU Research: UHPC Connections + SMA or Self Centering PS

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Other Options: Seismic Design and Resiliency of CFST Foundation

19FIU – UTC: In-Depth Web Training September 10, 2019: 11:00 am (EST)

Latest Seismic ABC Applications

Khashayar Nikzad, Principal Engineer, Trantech

Module 1 – Latest Seismic ABC Applications

Part 2: Design Examples

Precast Concrete Bent Cap – Design Example

Construction Sequence20

Precast Concrete Bent Cap – Design Example

o This design example is to demonstrate the design of a staged-construction bent cap including precast, nonprestressed U-beam section.

o Utilizing a Stage 1 precast bent cap can reduce the amount of formwork that is needed to construct the bent cap, which can reduce construction time and costs.

o The precast U beam weighs only one-third of the weight of a solid section and facilitates cap beam-to-column rebar connection.

o Stirrups for Stage 2 are placed before casting the precast U beam using mechanical couplers. These stirrups extend out of the Stage 1 composite section to connect with end diaphragm between the beam ends.

o In Stage 2, additional reinforcing bars are placed in the space between the beam ends. Concrete is placed around the rebar for the end diaphragm, which is also considered as part of the bent cap in the final stage.

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Stage 1 Bent Cap Designo Precast U-Beam

o Check Flexural, Shear, and Torsional Capacity

o Check for Stem Wall Flexural Capacity due to Wet Concrete

o Composite Section Design

Stage 2 Bent Cap Designo Superimposed Dead and Live Loads

o Extreme Event Load Demands

o Check Flexural and Shear Capacity

Additional Bent Cap Design Checks

Precast Concrete Bent Cap – Design Example22

Precast U-Beam – Non-compositef’c_PC = 9 ksiA = 1,488 in.2I = 501,153 in.4yt = −38.82 in. yb = 20.18 in.St = 12,909 in.3Sb = 24,837 in.3de_pos = 54.75 in.de_neg = 54.94 in.

Precast Concrete Bent Cap – Design Example

Precast U-Beam – Compositef’c_PC = 9 ksif’c_CIP = 4 ksiA = 4,142 in.2I = 1,245,573 in.4yt = −30.29 in. yb = 28.71 in.St = 41,127 in.3Sb = 43,379 in.3de_pos = 54.75 in.de_neg = 55.13 in.

𝑛𝑛 =𝐸𝐸𝑐𝑐_𝐶𝐶𝐶𝐶𝐶𝐶𝐸𝐸𝑐𝑐_𝑃𝑃𝑃𝑃

=40.33

90.33 = 0.80

tw bc

B

H hc

ts

Stage 1

B = 7’ ; bc = 5’-8” ; H = 4’-11”hc = 4’-3”; ts = 8”; tw = 8”

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Compositef’c_PC = 9 ksi for PC U-Beam f’c_CIP = 4 ksi for CIP concreteA = 6,493 in.2I = 12,300,569 in.4yt = −92.10 in. yb = 57.30 in.St = 133,497 in.3Sb = 214,937 in.3de_pos = 145.13 in.de_neg = 146.38 in.

Precast Concrete Bent Cap – Design ExampleStage 2

30”

149.4”

59”

84”

58.8”

8”

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• DC = 5.7 K/Ft

• Factored DC = 7.2 K/Ft

• Check Flexural Capacity

Positive moment - Bottom of bent cap between columnsDemand: Mu = 161 ft-kipsCapacity: ɸMn = 1,738 ft-kips [2 layers - 6 No. 7 bars]

Negative moment - Top of bent cap over the columnsDemand: Mu = 129 ft-kipsCapacity: ɸMn = 1,278 ft-kips [2 layers - 4 No. 7 bars]

Precast Concrete Bent Cap – Design ExampleStage 1 – Non-composite25

• Check Shear Capacity 𝜑𝜑𝑣𝑣𝑉𝑉𝑐𝑐 = 𝜑𝜑𝑣𝑣0.0316𝛽𝛽𝛽𝛽 𝑓𝑓𝑓𝑐𝑐𝑏𝑏𝑣𝑣𝑑𝑑𝑣𝑣 (LRFD Eq. 5.7.3.3-3)𝜑𝜑𝑉𝑉𝑉𝑉𝑠𝑠 = 𝜑𝜑𝑉𝑉

𝐴𝐴𝑣𝑣𝑓𝑓𝑦𝑦𝑑𝑑𝑣𝑣(𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡)𝑠𝑠

(LRFD Eq. 5.7.3.3-4)

𝛽𝛽 = 4.8(1+750𝜀𝜀𝑠𝑠)

(LRFD Eq. 5.7.3.4.2-1)𝜃𝜃 = 29 + 3500𝜀𝜀𝑠𝑠 (LRFD Eq. 5.7.3.4.2-3)

𝜀𝜀𝑠𝑠 =�𝑀𝑀𝑢𝑢𝑑𝑑𝑣𝑣+𝑉𝑉𝑢𝑢𝐸𝐸𝑠𝑠𝐴𝐴𝑠𝑠

(LRFD Eq. 5.7.3.4.2-4)Parameters at Critical Shear SectionMu = 129 ft-kips; Vu = 64 kips; dv = 0.9 x 54.75 = 49.3 in.; Es = 29,000 ksiAs = 6.32 in.2; Ɛs = 0.00052; β = 3.45; θ = 30.8 degɸvVn = ɸvVc + ɸvVs = 693 kips [4 leg #5 stirrups spacing at 12 in. = 1.24 in.2 ]• Check Min Shear Reinforcement𝐴𝐴𝑣𝑣 ≥ 0.0316𝑓𝑓′𝑐𝑐

𝑏𝑏𝑣𝑣𝑠𝑠𝑓𝑓𝑦𝑦

= 0.30 𝑖𝑖𝑛𝑛2 (LRFD Eq. 5.7.2.5-1)• Design Stem Wall for Wet Concrete Pressure

Precast Concrete Bent Cap – Design ExampleStage 1 – Non-Composite26

DC Reactions at Bent Cap

Precast Concrete Bent Cap – Design ExampleStage 1 – Composite

Check Flexural CapacityPositive moment - Bottom of bent cap between columns Demand: Mu = 989 ft-kipsCapacity:ɸMn = 1,785 ft-kips[No additional bars required]

Negative moment - Top of bent cap over the columns at centerline column Demand: Mu = 1,449 ft-kipsCapacity:ɸMn = 1,888 ft-kips[Additional 8 No. 5 bars are required.]

#4 Tie

2-legs #6 stirrup #5 @10”

EF

8-#5

Deck Reinf.6-#7

#5 @12”

Component(Description) Exterior Beam (Kips) Interior Beam (Kips)

Beam 100.9 100.9Slab 84.8 87.2

Slab Haunch 20.5 20.5Int Diaphragm 13.6 27.3

Total 219.8 235.9

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Precast Concrete Bent Cap – Design ExampleStage 1 – Composite

Check Shear Capacity• Per Geometry, assume D regions (AASHTO

LRFD 5.5.1.2)• Design per Strut & Tie Method, STM

(AASHTO LRFD 5.8.2)• STM not shown for brevity• Interface shear• Crack control reinforcing• Torsional capacity

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Precast Concrete Bent Cap – Design ExampleStage 2

Strength I Demands

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Component(Description) Exterior Beam (Kips) Interior Beam (Kips)

Barrier 23.7 23.7

Future Overlay (22 psf) 8.6 8.6

Total 32.3 32.3

LOAD CASES

(1) DL + LL Mneg (2) DL + LL Mpos

Analysis Section

Moment (Kip-ft) Shear (Kip) Moment

(Kip-ft) Shear (Kip)

A −1,969 584 −1,233 369B −1,733 −708 −926 −844C 472 162 2310 317

Precast Concrete Bent Cap – Design ExampleStage 2

Extreme Event Demands

Peak Ground Acceleration, PGA = 0.35 g (LRFD 3.10.2.1)Acceleration at 0.2 sec., Ss =0.80 (LRFD 3.10.2.1)Acceleration at 1.0 sec., S1 =0.36 (LRFD 3.10.2.1)Site Effects, Site Class A (found on rocks) (LRFD 3.10.3.1)Site Factors, Fpga = 0.8, Fa = 0.8, Fv = 0.8 (LRFD 3.10.3.2)Essential Bridge, use 1000-yr return period event (LRFD 3.10.5)Seismic Performance Zone, Seismic Zone 3 (LRFD 3.10.6)

Pier 2 Pier 3Mx (trans) = 870 ft-kips 976 ft-kipsMy (long) = 464 ft-kips 401 ft-kips

Pier 2 Pier 3Mx (trans) = 2,901 ft-kips 3,088 ft-kipsMy (long) = 261 ft-kips 216 ft-kips

Longitudinal EQ = 1.0Long + 0.3Trans

Transverse EQ = 0.3Long + 1.0Trans

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Precast Concrete Bent Cap – Design ExampleStage 2

Flexural CapacityUse lesser value of elastic modal analysis load combination and plastic capacity of the column:

Positive Moment - Bottom of bent cap between columns Demand: Mu = 3,088 ft-kipsCapacity:ɸMn = 8,472 ft-kips[No additional rebar is required]

Negative Moment - Top of bent cap over the columns Demand: Mu = 3,088 ft-kipsCapacity:ɸMn = 4,634 ft-kips[Additional 6-No.7 bars in bridge deck is required.]

Mu = 3,088 ft-kips Mp = 3,776 ft-kips

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Precast Concrete Bent Cap – Design ExampleStage 2

Shear Capacity – Extreme Event

Parameters for Shear DemandMp = 3,776 ft-kips

Article 3.10.9.4.3c, an overstrength resistance factor equal to 1.3 can be used for reinforced concrete columns.

Mpo = 1.3 x 3,776 ft-kips = 4,909 ft-kipsVp = 214 kipsCenter of gravity to bottom fiber, Yb = 57.30 in.Mo = 4,909 + 214 x 57.30/12 = 5,931 ft-kipsLb = 18 ftVo = 2Mo / Lb = 2 x 5,931/18 = 659 kips

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Precast Concrete Bent Cap – Design ExampleStage 2

Shear Capacity – Extreme Event

Parameters for Shear Design with Extreme Event Load Case

Mu = 5,931 ft-kips (less than ɸMn = 7,734 ft-kips, okay)Vu = 659 kipsdv = 0.9 x 146.38 = 131.74 in. (negative bending)Es = 29,000 ksiAs = 7.94 in2 (6 - #7, 14 - #5)Ɛs = 0.005208β = 0.978θ = 47.23 degThe shear capacity of the section is calculated as follows:

ɸvVn = ɸvVc + ɸvVs = 0.9 x 244.4 + 0.9 x 804.3 = 944 kips [2 leg #6stirrups spacing at 8 in.]

The shear capacity is greater than the overstrength shear of659 kips. OK

#4 Tie

2-legs #6 stirrups @8”#5 @10”

EF

8-#5

Deck Reinf.6-#7

#5 @12”

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Precast Concrete Bent Cap – Design ExampleStage 2

Shear Capacity – Strength Limit State

• Per Geometry, assume D regions (AASHTO LRFD 5.5.1.2)

• Design per Strut & Tie Method, STM (AASHTO LRFD 5.8.2)

• STM not shown for brevity• Crack control reinforcement to be provided per

AASHTO LRFD 5.8.2.6

Additional Checks• Positive moment reinforcement extension

#4 Tie

2-legs #6 stirrups @8”#5 @10”

EF

8-#5

Deck Reinf.6-#7

#5 @12”

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Bijan Khaleghi, Bijan.Khaleghi@wsdot.wa.gov

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Thank YouKhashayar Nikzad,knikzad@trantecheng.com