Progression of Structural Design Approaches

Naveed Anwar, AIT Solutions
Progression of Structural Design Approaches
Design ofTall Buildings:Trends and Advancements
for Structural Performance
Bangkok-Thailand
November 7-11, 2016
NaveedAnwar, PhD

Naveed Anwar, AIT Solutions 2
Trends and Advancements in for Structural Performance
Why this Seminar andWorkshop ?
And why is this topic imporant

Demand and Complexity is Increasing

Percentage of Urbanized World
4

World’s Population Urban-to-Rural Ratio
5
(www.un.org)

Visions
6
Japan, 4000m Sky MileTower, 1700 m JapanDubai City Tower, 2400 m One DubaiTower,
1008 m

The Reality
7

Source: CTBU Report, 2015

TheTwistingTurningTowersTrend

Tall Buildings in Bangkok
(> 200m)

Buildings and Structures are expected to be
• Safe
• Secure
• Serviceable
• Reliable
• The contents of the structures are often much more valuable than structure itself
• The loss of service/operations/business is a often larger than repair costs
• Protective
• Friendly
• Sustainable
• Affordable

Needs Changes in Structural
Design Approaches

18
Is my Structure safe?
(What level of Richter earthquake my structure sustain?
Or what tornado level can it withstand,
or is it safe for explosions or
How long can it withstand the fire?)

How long do we have
before the building will
collapse in this fire?
- Asks the Fire Chief from the structural
engineer
1974

The Towering Inferno (1974)
20
https://www.youtube.com/watch?v=FagbC09BO2o

Evolution of our Understanding of Structures
Limits on the allowable stresses to
achieve in-direct FOS
Explicit consideration of
partial FOS.
Formulation of limit
state design principles.
Formulation of ultimate
strength.
The recognition of the
difference between brittle
and ductile failure.
The introduction of
capacity based design
approaches.
Performance based
design and more explicit
linkage between demand
and performance.
Risk integrated based design, and
a more and holistic approach
towards consequence based
engineering.

Design Approaches
Intuitive
Design
Code Based
Design
Performance
Based Design
Consequences
and Risk Based
Design
Resilience
Based Design

Design Approaches
Intuitive
Design
Code
Based
Design
Performance
Based Design
Consequences
and Risk
Based Design
Resilience
Based Design

Development of Formal Buildings Codes
24
“Rebuilding
of London
Act” after the
“Great Fire of
London” in
1666 AD.
In 1680 AD,
“The Laws of
the
Indies” Spani
sh 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 Internat
ional
Building
Code (IBC)
by (ICC).
European
Union,
the Eurocodes.

The Modern Codes – With “intent” to make buildings safe for public
25
(ACI 318 – 11)
Extremely Detailed
prescriptions and
equations using
seemingly arbitrary,
rounded limits with
implicit meaning
(IS 456-2000)

The General Code Families
26
UBC, IBC
ACI, PCI, CRSI,
ASCE, AISI,
AASHTO
British,CP and
BS
Euro-codes
China, USSR,
Japan

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 years, should we upgrade our structures every 3 or 5
years to conform ?
• Codes intend for “Life Safety”, not damage limits or cost implications
27

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
28

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

30

The First Building Code: Code of Hammurabi (1792 BC to 1750 BC)
31
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.

Design Approaches
Code Based
Design
Performance
Based Design
Consequences and
Risk Based Design
Resilience Based
Design

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”
33

Define Performance Levels
34
Based on FEMA 451 B

Link the Hazard to Performance Levels
35
Structural Displacement
LoadingSeverity
Resta
urant
Resta
urant
Resta
urant
Hazard
Vulnerability
Consequences

Is this acceptable?
Even though it satisfies CBD and PBD

Design Approaches
Code Based
Design
Performance
Based Design
Consequence
and Risk
Based Design
Resilience Based
Design

Beyond PBD
• For public, the performance
criteria still does reduce the
effects of the events
• Insurance companies want to
have greater reliability of
assessment of risk and
damages
38

Questions still un-answered
• What if the chance that performance level is not
achieved?
• What is the risk ?
• What are the consequences?
• What if the performance levels are not sufficient?
Code based was implicit, with
not confirmation of response
PBD is explicit, can help to
confirm the response and
performance level

Why do we need to go Beyond PBD
• For public and society, the performance criteria still does reduce the effects of the
events, but it can reduce the risk level
• 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

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).
41
The trigger of an event is not important,
the consequences of an event are

Consequence Based Engineering
• “Structural consequence and non-structural effects”
determined entirely from the analysis of structural
member as well as overall system behavior.
• Proceeds through the analysis of expected system
consequences, irrespective of the event triggering
these consequences.
• Requires the structural members to be designed for
variable reliability levels, depending upon their
contribution in causing adverse system
consequences.
42

Risk Based Design Process
Safety Studies
(Probability and
Consequence Analysis)
Risk
Quantification
Safety Critical
Element
Design
Accidental
Load
Structure
Design

Special Purposes Guidelines from USA
44
Applied
Technology
Council
(ATC)
Federal
Emergency
Manageme
nt Agency
(FEMA) and
National
Earthquake
Hazards
Reduction
Program
(NEHRP)
PEER
Guidelines
forTall
Buildings
Tall
Buildings
Initiatives
(TBI)
CTBUH
Guidelines

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 needed
45

Design Approaches
Code Based
Design
Performance
Based Design
Consequences
and Risk Based
Design
Resilience
Based Design

RESILIENCE
Economic
Social
Organizational
Technical
Resourcefulness
Redundancy
Rapiditty
Robustness
Lower
Consequences
Faster
Recovery
More Reliability
4 Dimensions of
Resilience
4 Properties of
Resilience
3 Results of Resilience
47

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)
48
Economic Loses
Loss of
Community
and Culture
Loss of
Quality of
Life
Go Beyond Life Safety

Link Performance to other Indicators
49
Restaurant Restaurant
Restaurant
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

Green Buildings Resilient Buildings
50
Main authors : Arup
Supported by USRC and many others

ARUP

Tools: How to design efficiently?

The Growing Computational Requirements
• Dynamic Analysis
• Nonlinear modelling
• Nonlinear Time History Analysis
• Progressive Collapse
• Staged construction analysis
• A new and major concern for structural safety
• Structure should not collapse completely if one or two elements are
“destroyed”
• Backup systems, alternate load paths, additional redundancy

The Role of Computers and Software
54
• Initially, computers were used to
program the procedure we had
• Now, we develop procedures that
are suited for computing

Design Approaches evolved to match computing revolution
55

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
56

Mobile computing might change how we design
57

Can we make it safe, sustainable and resilient?
58

Thank you
View publication statsView publication stats

Progression of Structural Design Approaches

Recommandé

Recommandé

Contenu connexe

Tendances

Tendances (6)

Similaire à Progression of Structural Design Approaches

Similaire à Progression of Structural Design Approaches (20)

Plus de AIT Solutions

Plus de AIT Solutions (18)

Dernier

Dernier (20)

Progression of Structural Design Approaches