Module 1 – Outline o LRFD Bridge Seismic Design Requirements o ABC Seismic Research and Implementation o Innovations in Bridge Seismic Design o 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 1
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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
1
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
2
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.
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)
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
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.]
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)
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