Seismic Design Philosophies From Prescription to Performance

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

2Seismic Design Philosophies – From Prescription to Performance (Fawad A. Najam)

Why This Topic?

Ground Shaking Hazard: Kashmir Earthquake (2005), Balakot,

Pakistan (Magnitude = 7.6 ~ 7.8)


What are the causes of

Earthquakes?


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

6

Internal

Structure of

Earth


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


Continental Drift


Earth’s 14 Tectonic Plates and their Movements


Where do Earthquakes Occur ?

11

The Case of

Pakistan

12

Seismicity of

Pakistan

13

Kashmir

Earthquake (2005)

Balakot, Pakistan

(Magnitude = 7.7)

Final Comprehensive Examination 14

Session 2:

The Scope of Performance-based Seismic Design in Pakistan


Ground Shaking Hazard: Wenchuan Earthquake (2008), ChinaMagnitude = 8.0


BPKP Building (Sewon, Yogyakarta)

Ground Shaking Hazard: Yogyakarta Earthquake (2006), Indonesia

Magnitude = 6.2


Surface Rupture Hazard: The 1999 Chi-Chi earthquake, Taiwan


The 1999 Chi-Chi earthquake, Shih-Kang Dam


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


Tokachi-oki EQ, Hokkaido (2003)


Underground Pipe Failure in Baguio, Philippines (Luzon Earthquake, 1990)


Earthquake-induced Landslide in Wenchuan County, China(Wenchuan Earthquake, 2008)

Introducing AIT SolutionsFinal Comprehensive Examination 23

Bhuj earthquake 2001 Irrigation Dams


Tsunami generated by an Earthquake

Generation

Propagation

Inundation


Maximum Water Level

Khao Lak, Phang-Nga


Fires resulting from Earthquakes (Kobe EQ, 1995)


Fires resulting from the

Earthquake (Kobe EQ, 1995)


Seismic Design Philosophies – From Prescription to Performance

29

Why Buildings

Collapse under

Earthquakes?


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


Global Seismic Hazard Map


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


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.


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


“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


Capacity > Demand

𝑪

𝑫= 𝑭𝒐𝑺 𝐶 = 𝐷 × 𝐹𝑜𝑆

𝐶

𝐹𝑜𝑆= 𝐷

𝐶

𝐹𝑜𝑆1= 𝐷 × 𝐹𝑜𝑆2

Ensuring Safety through Factor of Safety!


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.


The General Code Families

UBC, IBC

ACI, PCI, CRSI, ASCE,

AISI,

AASHTO

British, CP and BS

Euro-codesChina, USSR,

Japan


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)


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.

42

The Elastic

Behavior of

Structures

Strain

Stre

ss

fy

0.5fy

Unused Strength and Ductility

43

The “Real

Behavior” of

Structures


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


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


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


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


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”


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


Define Performance Levels

Based on FEMA 451 B

0 % Damage or Loss 99 %


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


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


Performance-based design can be applied to any type of loads, but is typically suitable and targeted for

earthquake loads


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”


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


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


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


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


Performance-based Design Process

Acceptance Criteria for Primary Components


Performance Based Design Process

Acceptance Criteria for Secondary Components


How to Work with PBD

Architect

Structural Engineer

PBD Specialist

PBD Peer Reviewer

Site Specific Consultant

Client


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

64

Is this acceptable?Even though it satisfies CBD and PBD


Evolution of Structural Design Approaches

Intuitive Design

Code-based Design

Performance-based Design

Consequences and Risk Based Design

Resilience Based Design


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.


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?


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


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.


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


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



PC/Mac

ETABS Cloud Viewer

ETABS Cloud Viewer is a mobile and web application for viewing CSI ETABS models

iOS

Android

Tablets


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


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

76

Thank you for your attention

Contact:

[email protected]


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

Documents

Seismic Design Philosophies From Prescription to Performance