seismic design philosophies from prescription to performance
TRANSCRIPT
One-day CPD Seminar at
Dr. Fawad A. NajamDepartment of Structural Engineering
NUST Institute of Civil Engineering (NICE)
National University of Sciences and Technology (NUST)
H-12 Islamabad, Pakistan
Cell: 92-334-5192533, Email: [email protected]
Swedish College of Engineering and Technology (SCET), Wah Cantt
Seismic Design Philosophies – From Prescription to Performance
4Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
What are the causes of
Earthquakes?
5Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
In ancient Japanese folklore, a giant catfish (Namazu) lives in the mud beneath the earth. It is guarded
by the god Kashima who restrains the fish with a stone. When Kashima let his guard fall, Namazu
thrashes its body, causing violent earthquakes.
The Causes of Earthquakes
7Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
The basic idea of “plate tectonics” is that the earth’s outer shell (called the lithosphere)
consists of several large and fairly stable slabs of solid rock called plates.
The thickness of each plate is about 80 km. The plate moves horizontally, relative to neighboring
plates, on a layer of softer rock.
Plate Tectonics
9Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Earth’s 14 Tectonic Plates and their Movements
10Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Where do Earthquakes Occur ?
Final Comprehensive Examination 14
Session 2:
The Scope of Performance-based Seismic Design in Pakistan
Final Comprehensive Examination 15
Ground Shaking Hazard: Wenchuan Earthquake (2008), ChinaMagnitude = 8.0
Final Comprehensive Examination 16
BPKP Building (Sewon, Yogyakarta)
Ground Shaking Hazard: Yogyakarta Earthquake (2006), Indonesia
Magnitude = 6.2
Final Comprehensive Examination 19
Overturned building in Adpazari, Turkey in the 1999 Kocaeli EQ
A building in Dagupan,
Philippines after the
1990 Luzon EQ
Soil Liquefaction HazardLoss of Bearing Capacity
Final Comprehensive Examination 21
Underground Pipe Failure in Baguio, Philippines (Luzon Earthquake, 1990)
Final Comprehensive Examination 22
Earthquake-induced Landslide in Wenchuan County, China(Wenchuan Earthquake, 2008)
Introducing AIT SolutionsFinal Comprehensive Examination 24
Tsunami generated by an Earthquake
Generation
Propagation
Inundation
31Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Future ground
shaking
Structure
Linear/Nonlinear
Analysis Model
Characterization of
Seismic Ground
Motions
Estimation of Linear/Nonlinear
Seismic Demands
• Global-level Responses
• Inter-story Responses
• Component-level
Responses
The Earthquake Problem
Seismic Waves
Soil
Epicenter
Hypocenter
(Focus)
Fault
AttenuationSeismic waves lengthen and diminish in strength
as they travel away from the ruptured fault.
Site ResponseGround motion can
be amplified by soil
Site
Seismic WavesHypocenter
(Focus)
Fault
Soil
Site
Site ResponseGround motion can
be amplified by soil
Attenuation
Epicenter
32Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Global Seismic Hazard Map
33Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Evolution of Structural Design Approaches against Earthquakes
Intuitive Design
Code-based Design
Performance-based Design
Consequences and Risk Based Design
Resilience Based Design
Focus of this talk
34Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
The First Building Code: Code of Hammurabi (1792 BC to 1750 BC)
Clause 229:
If a builder builds a house for someone, and does not construct it properly, and the house
which he built falls in and kills its owner, then that builder shall be put to death.
35Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Ancient Building Code: Laws of Moses
“In case you build a new house, youmust also make a parapet for your roof,that you may not place bloodguilt uponyour house because someone fallingmight fall from it”.
- The Bible, Book of Deuteronomy, Chapter 22, Verse 8
36Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
“Structural Design is the process of proportioning the structure to safely
resist the applied forces in the most cost effective and friendly manner”
A systematic investigation of the stability,
strength and rigidity of structures
Where Safety is a prime concern
37Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Capacity > Demand
𝑪
𝑫= 𝑭𝒐𝑺 𝐶 = 𝐷 × 𝐹𝑜𝑆
𝐶
𝐹𝑜𝑆= 𝐷
𝐶
𝐹𝑜𝑆1= 𝐷 × 𝐹𝑜𝑆2
Ensuring Safety through Factor of Safety!
38Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Development of Formal Buildings Codes
“Rebuilding of London
Act” after the “Great Fire of
London” in 1666 AD.
In 1680 AD, “The Laws of
the Indies” Spanis
h Crown
London Building Act of
1844.
In USA, the City
of Baltimore first building
code in 1859.
In 1904, a Handbook of the Baltimore
City
In 1908 , a formal
building code was drafted
and adopted.
The International
Building Code (IBC) by (ICC).
European Union,
the Eurocodes.
39Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
The General Code Families
UBC, IBC
ACI, PCI, CRSI, ASCE,
AISI,
AASHTO
British, CP and BS
Euro-codesChina, USSR,
Japan
40Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
The Modern Codes – With “intent” to make buildings safe for public
(ACI 318 – 11)
Extremely detailed prescriptions
and equations using seemingly
arbitrary, rounded limits with
implicit meaning
(IS 456-2000)
41Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Design for Seismic Resistance and Extreme Events
• Force/stress based design
• Assume reduced forces, limit the stresses.
• Displacement based design
• Allow force D/C to exceed, as long as displacements can be limited.
• Capacity based design
• Put “fuses” in the structure limit the force capacity, hence the demand.
• Energy based design
• Total energy input is collectively resisted by kinetic energy, the elastic strain energy and energy dissipated through plastic deformations and damping.
Introducing AIT SolutionsFinal Comprehensive Examination 44
Progression of Seismic Resistance Design
Historical Approach:Earthquake forces proportional tobuilding mass (Vdes = 5 - 10% of Wt),
Traditional Codes:Elastic earthquake forces reduced forlinear design (Vdes = Vmax /R)
Historical Approach:
Earthquake forces proportional tobuilding mass (Vdes = 5 - 10% of Wt),
Traditional Codes:
Elastic earthquake forces reduced forlinear design (Vdes = Vmax/R)
Lack of Knowledge on
Earthquake Demand
and Building Capacity
Linear Elastic Building
Response
V
Vdes
V
Vdes
Elastic Forces
reduced for
Design by R
Inelastic
Response
YieldMax
45Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Are All Buildings Codes Correct ?
• If they differ, can all of them be correct ?
• Did we inform the structures to follow which code when earthquake or hurricane strikes ?
• Codes change every 3 or 5 years, should we upgrade our structures every 3 or 5 years to conform ?
• Codes intend for “Life Safety”, not damage limits or cost implications
46Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Prescriptive Codes – A Shelter
• Public: • Is my structure safe ?
• Will it be damaged, how much, how long to repair
• Structural Engineer:• Not sure, but I did follow the “Code”
As long as engineers follow the code, they can be sheltered by its provisions
47Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Shortcomings of Code Based Design for Tall Buildings
• Traditional codes govern design of general, normal buildings
Over 95% buildings are covered, which are less than about 50 m
• Not specifically developed for tall buildings > 50 m tall
• Prescriptive in nature, no explicit check on outcome
• Permit a limited number of structural systems
• Do not include framing systems appropriate for high-rise
• Based on elastic methods of analysis
• Enforce uniform detailing rules on all members
• Enforce unreasonable demand distribution rules
• Do not take advantage of recent computing tools
48Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Performance Based Design (PBD)
• An approach in which structural design criteria are expressed in terms of achieving a set of performance objectives or levels.
• Ensures structures reaches specified demands level in both service and strength design levels.
• Why it was needed?
• Traditional codes not suitable/adequate
• Explicit verification not specified or required in most codes
• Public does not care about the code, or theories or procedures, they care about “safety” and ‘performance”
49Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Prescriptive vs. Performance
Approach Procedure Outcome
Prescriptive
(emphasis on procedures)
Specify “what, and how to
do”
Make Concrete: 1:2:4
Implicit Expectation
(a strength of 21 MPA is
expected)
Performance Based
Approach
(emphasis on KPI)
What ever it takes
(within certain bounds)
Explicit Performance
Concrete less than 21 MPa is
rejected
50Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Define Performance Levels
Based on FEMA 451 B
0 % Damage or Loss 99 %
51Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Link the Hazard to Performance Levels
Structural Displacement
Lo
adin
g S
ever
ity
Resta
urant
Resta
urant
Resta
uran
t
Haz
ard
Vulnerability
Consequences
52Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Link Performance to other Indicators
Restaurant Restaurant
Resta
uran
t
Operational (O) Immediate Occupancy (IO) Life Safety (LS) Collapse Prevention (CP)
0 % Damage or Loss 99 %
Ref: FEMA 451 B
CasualtiesLowest Highest
Rehab Cost to Restore after eventLowest Highest
Retrofit Cost to Minimize ConsequencesHighest Lowest
Downtime for RehabLowest Highest
Impact on Sustainability of CommunityLowest Highets
53Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Performance-based design can be applied to any type of loads, but is typically suitable and targeted for
earthquake loads
54Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Explicit Performance Objective in PBD
Performance based design investigates at least two performance objectives
explicitly
Service-level Assessment
Negligible damage with frequent hazards
(Earthquake having a return period of about 50)
Collapse-level Assessment
Collapse prevention under extreme hazards
(the largest earthquake with a return period of 2500 years)
Codes arbitrary
“Design Level”
55Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Performance Objectives
Level of Earthquake Seismic Performance Objective
Frequent/Service (SLE): 50% probability of
exceedance in 30 years (43-year return period)
Serviceability: Structure to remain essentially
elastic with minor damage to structural and non-
structural elements
Design Basis Earthquake (DBE): 10% probability
of exceedance in 50 years (475-year return period)
Code Level: Moderate structural damage;
extensive repairs may be required
Maximum Considered Earthquake (MCE): 2%
probability of exceedance in 50 years (2475-year
return period)
Collapse Prevention: Extensive structural
damage; repairs are required and may not be
economically feasible
56Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Performance Level Definitions
Owner
Will the building be safe?
Can I use the building after the hazard?
How much will repair cost in case of damage?
How long will it take to repair?
Engineer
amount of yielding, buckling, cracking, permanent deformation, acceleration, that
structure, members and materials experiences
Need a third party to ensure public safety and
realistic Performance
Guidelines
Peer Review
Cracking in Shear Walls
3D View
A 44-story Case Study Building
Elevation View
Pushover Curve (Strong Direction)
Base Shear vs. Roof Drift Ratio
No Crack
Cracked
58Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Performance Based Design Process
Analyzing Linear Elastic Model for
Code Based Design Loading
Formulation & Analysis of
Nonlinear Model of Real Building
Results Extractions and Processing
Interpretation of Results for Decision
Making
59Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Judging Performance Acceptability
• Acceptance criteria are indicators of whether the predicted performance is adequate for
• Local (component based)
Example: Drift ratio, structural component deformation
• Global (overall structure-based)
Example: Roof drift , base shear
60Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Performance-based Design Process
Acceptance Criteria for Primary Components
61Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Performance Based Design Process
Acceptance Criteria for Secondary Components
62Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
How to Work with PBD
Architect
Structural Engineer
PBD Specialist
PBD Peer Reviewer
Site Specific Consultant
Client
63Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Special Purposes Guidelines from USA
Applied
Technology
Council (ATC)
Federal
Emergency
Management
Agency
(FEMA)
National
Earthquake
Hazards
Reduction
Program
(NEHRP)
PEER
Guidelines for
Tall Buildings
Tall Buildings
Initiatives (TBI)
CTBUH
Guidelines
65Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Evolution of Structural Design Approaches
Intuitive Design
Code-based Design
Performance-based Design
Consequences and Risk Based Design
Resilience Based Design
66Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Beyond PBD
• For public, the performance
criteria still does reduce the
effects of the events.
• The non structural damage is not
acceptable in modern buildings
• The disruption and loss goes
much beyond the building
• Insurance companies want to
have greater reliability of
assessment of risk and damages.
67Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Questions still un-answered
• What is the chance that performance level is not achieved?
• What is the risk?
• What are the consequences?
• What if the performance levels are not sufficient?
68Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Consequence Based Engineering
• It is not enough to say “Cracking and non-structural damage is acceptable, as long as structure does not collapse”
• A natural extension of the performance-based design approach
• Structural consequences > DDD (dollars, deaths and downtime) (Porter, 2003).
The trigger of an event is not important,
the consequences of an event are
69Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
What Next: What is still missing
• Adequacy, Performance and Risk reduction of Structure alone is not enough.
• Structure serves a purpose in society, economy, community > Should be integrated with other aspects.
• A more holistic approach, beyond structural design is needed.
70Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Resilience Based Earthquake Design
• A holistic approach which seeks to identify all
hazard-induced risks (including those outside the
building envelope) and mitigate them using
integrated multi-disciplinary design and contingency
planning to achieve swift recovery objectives in the
aftermath of a major earthquake.
• The key principle in resilience-based design is to
limit expected damage to structural and
architectural components and egress systems
(elevators, stairs, and doors).
Economic Loses
Loss of Community and Culture
Loss of Quality of Life
Go Beyond Life Safety
71Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
The Role of Computers and Software
• Initially, computers were used to program the procedure we had
• Now, we develop procedures that are suited for computing
71
73Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
PC/Mac
ETABS Cloud Viewer
ETABS Cloud Viewer is a mobile and web application for viewing CSI ETABS models
iOS
Android
Tablets
74Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
A Swing Towards the AI
• Rich Pictures
• Analytical Hierarchy Process (AHP)
• Artificial Neural Networks (ANN)
• Genetic Algorithms (GA)
• Expert Systems (ES)
• Fuzzy Logic
• Deep Thinking
• Big Data and Data Mining
75Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Using AI in Structural Design Process
Architectural Design
Preliminary Sizing
Structural Modeling
Structural Analysis
Code Based Design
Performance Based Design
Iterative, computationally intensive and time consuming
Experience Based Prediction
77Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)
Acknowledgement
• The material for the preparation of these lectures slides are taken from different sources.
Prof. Dr. Pennung Warnitchai
• The primary source for these lecture slides are
the lectures of Dr. Naveed Anwar and Prof. Dr.
Pennung Warnitchai at Asian Institute of
Technology (AIT), Thailand
• Some other references of this training material
include the following.
• Online Training Material from TBI, PEER and IRIS
• Online Educational Resources from FEMA
• Class Notes of Prof. Dr. Worsak Kanok-Nukulchai at Asian Institute of Technology (AIT), Thailand
• Lectures of Dr. Punchet Thammarak at Asian Institute of Technology (AIT), Thailand
• The material is taken solely for educational purposes. All sources are duly acknowledged.
Dr. Naveed Anwar