Performance Based Design and Evaluation of Concrete Dams Yusof - PowerPoint PPT Presentation

Performance ‐ Based Design and Evaluation of Concrete Dams Yusof Ghanaat Quest Structures, Inc. Orinda, California, USA

Performance ‐ based Design Standard Procedures Performance ‐ based Procedures • Are based on simple stress • Design/evaluate a dam to have checks and limit equilibrium a predictable performance for analysis to avoid collapse and specified levels of seismic protect life hazard • Performance and hazard are • Acceptance based on not well defined substantiated performance level in terms of damage • May be used for non ‐ critical thresholds, permanent dams and screening purposes displacements, not FoS

Presentation Outline Design/Evaluation Criteria • – Ground motions – Performance levels – Performance goals – Design requirements Analysis and evaluation procedures – Performance evaluation of a gravity dam • – Damage thresholds with linear/nonlinear analysis • Performance evaluation of an arch dam – Damage thresholds with linear/nonlinear analysis Summary •

Design/Evaluation Earthquakes OBE – Operating Basis Earthquake • – 50% probability of exceedance in service life of structure – Serviceability performance MDE – Maximum Design Earthquake • – 1/3,000 to 1/10,000 AEP recommended by USSD – For dams it is taken equal to MCE – Damage control performance • MCE – Maximum Credible Earthquake – Largest EQ on a specific fault or seismic source zone – Background seismicity, “random EQ”, or “floating EQ” – Collapse prevention

Design/Evaluation Earthquakes 84 th % Cascadia Interface has a 3000 ‐ yr RP 50 th % Cascadia Interface has a 900 ‐ yr RP

Design/Evaluation Earthquakes • Local fault 84 th % ground motion exceeds 10,000 ‐ year UHS • 84 th % Cascadia has a RP ≈ 3,200 years

Design/Evaluation Earthquakes 84 th % New Madrid ground motion at the site has a RP of just less than 2,475 years

Design/Evaluation Earthquakes Median “Random EQ” MCE in EUS exceeds 10,000 ‐ year UHS

Performance Levels Serviceability Performance (Linear Elastic Range) • Serviceability Performance – Operable immediately after Damage Control Performance (Non-linear Strain Hardening Range) OBE level earthquakes Collapse Prevention • Damage Control Performance Load (Non-Linear Strain Softening Range) – Damaged but not lose load resistance capability • Collapse Prevention Performance – Damage and movements could be severe but not lead to collapse Displacement

Performance Requirements Serviceability Performance (Linear Elastic Range) Load Ground Motion Elastic Deformation Displacement

Performance Requirements Serviceability Performance High (Linear Elastic Range) Tension Regions Damage Control Performance (Non-linear Strain Hardening Range) Load Ground Motion Tensile Overstressing & Cracking Displacement

Performance Requirements Serviceability Performance (Linear Elastic Range) Damage Control Performance (Non-linear Strain Hardening Range) Collapse Prevention Load (Non-Linear Strain Softening Range) Sliding & Rotational Stability Displacement

Performance Goals Both strength and Limited ductile behavior • • serviceability should be – Characterized by an elastic considered range and limited inelastic range followed by a complete – Strength requirement ensures or significant loss of strength that failure in shear, flexure, tension, or compression will – Dams exhibit limited ‐ ductile not occur behavior in flexure and brittle behavior in shear – Serviceability requirement is to ensure the project will function – But some residual capacity may without interruption, with little still exist due to dead load or no damage. effects that contribute to shear ‐ friction resistance and to overturning resistance

Design Requirements • Serviceability design • Strength design – Reduce the probability of – Reduce the probability of damage to an acceptable level collapse to an acceptable level – Select an appropriate OBE event – Select an appropriate MDE event in combination with appropriate in combination with specific design/evaluation procedures design/evaluation procedures and loading combinations and loading that ensure the structure will perform as Q S = Q D + Q L + Q OBE intended Q DC = Q D + Q L + Q MDE

Tiered Analysis and Evaluation Response • Estimate peak responses Spectrum • Evaluate using DCR’s Analysis Linear • Identify potential failure modes Time ‐ History • Evaluate using damage control Thresholds Analysis Nonlinear • Model/analyze major nonlinear mechanisms Time ‐ History • Estimate permanent offsets/compressive stresses Analysis • Perform post ‐ earthquake stability

Allowable DCR Values for RS Action Performance Objectives In terms of Stresses Serviceability Damage Control (OBE) (MDE) Tension due to flexure 1.0 1.5 Diagonal tension due to shear 0.8 0.9 Shear due to sliding 0.8 1.0

Gravity Dams Damage Threshold DCR < 1, Minor or No Damage Nearly linear ‐ elastic response • DCR < 2, Damage Acceptable If • Overstress < 15% • CID < 0.3(2 ‐ DCR) DCR > 2 , CID > Threshold • Damage is Significant • May need nonlinear analysis or retrofit

Example Gravity Dam Height = 74 m Crest Thickness = 9.75 m Base Thickness = 53.83 m

Earthquake Ground Motions Response Spectra and Acceleration TH’s

Linear Time ‐ History Stresses Max. = 855 psi (5.9 MPa) Max. = 1,800 psi (12.4 MPa)

Comparison with Thresholds

Nonlinear Analysis Stress Contours 200 psi = 1.4MPa Gap ‐ friction Elements

Nonlinear Response Histories 0.8 0.7 ) t (in 0.6 n 0.5 e m 0.4 ce la 0.3 isp D 0.2 20 mm 0.1 0.0 0 5 10 15 20 Time (sec)

Arch Dams Damage Threshold DCR < 1, Minor or No Damage • Nearly linear ‐ elastic response • Minor joint opening DCR < 2, Damage Acceptable If • Overstress < 20% • CID < 0.4(2 ‐ DCR) DCR > 2 , CID > Threshold Damage is Severe • May need nonlinear analysis or retrofit •

Arch Dams Nonlinear Time History Evaluation Overstressing • Contraction joint opening • Increased cantilever stresses • Unstable cantilever blocks Sliding Stability • Along dam ‐ foundation interface • Foundation/abutment rock wedges Acceptance Criteria Compressive stresses • • Amount of joint opening • Non ‐ recoverable block movements

Example Arch dam Height = 468 ft (142.6 m) Crest Length = 724 ft (220.7 m) Crest Thickness = 12 ft (3.7 m) Base Thickness = 52 ft (15.8 m)

Arch Dam Linear Response Exceeds Damage Threshold

Arch Dam Nonlinear Response Contraction and lift joints repeatedly open and close

Summary • A performance ‐ based approach • Analysis and evaluation was introduced for seismic design procedures for each performance and evaluation of concrete dams level with corresponding acceptance criteria were • How to design/evaluate dams to discussed with examples have a predictable performance for specified levels of seismic • These guidelines and provisions hazard was outlined were developed for the USACE and are being used by Federal, • Three seismic performance States, and dam engineering levels: serviceability, damage community in the United States control, and collapse prevention and abroad were defined

Linear Time History Damage Control Threshold