design of tall buildings: trends and advancements for...

Naveed Anwar, AIT Solutions

Progression of Structural Design Approaches

Design of Tall Buildings: Trends and Advancements for Structural Performance

Bangkok-Thailand

November 7-11, 2016

Naveed Anwar, PhD

Naveed Anwar, AIT Solutions 2

Trends and Advancements in for Structural Performance

Why this Seminar and Workshop ?

And why is this topic imporant

Demand and Complexity is Increasing

Percentage of Urbanized World

World’s Population Urban-to-Rural Ratio

(www.un.org)

Visions

Japan, 4000m Sky Mile Tower, 1700 m JapanDubai City Tower, 2400 m One Dubai Tower, 1008 m

The Reality

Source: CTBU Report, 2015

The Twisting Turning Towers Trend

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

Naveed Anwar, AIT Solutions18

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 orHow 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

The Towering Inferno (1974)

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

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” Spani

sh Crown

London Building Act of

In USA, the City

of Baltimorefirst building code in 1859.

In 1904, a Handbook of the Baltimore

In 1908 , a formal

building code was

drafted and adopted.

The International

Building Code (IBC) by (ICC).

European Union,

the Eurocodes.

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)

The General Code Families

UBC, IBC

ACI, PCI, CRSI, ASCE, AISI,

AASHTO

British, CP and BS

Euro-codesChina, USSR,

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

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

Naveed Anwar, AIT Solutions30

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.

Design Approaches

Code 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”

Define Performance Levels

Based on FEMA 451 B

Link the Hazard to Performance Levels

Structural Displacement

Vulnerability

Consequences

Is this acceptable?Even though it satisfies CBD and PBD

Design Approaches

Code Based Design

Consequence and Risk 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

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).

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.

Risk Based Design Process

Safety Studies (Probability and

Consequence Analysis)

Risk Quantification

Safety Critical Element

Design Accidental

Structure Design

Special Purposes Guidelines from USA

Applied Technology

Council (ATC)

Federal Emergency Management Agency

(FEMA) and

National Earthquake

Hazards Reduction Program (NEHRP)

PEER Guidelines

for Tall Buildings

Tall Buildings Initiatives

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

Design Approaches

Code Based Design

RESILIENCE

Economic

Social

Organizational

Technical

Resourcefulness

Redundancy

Rapiditty

Robustness

Consequences

Faster

Recovery

More Reliability

4 Dimensions of

Resilience

4 Properties of

Resilience

3 Results of Resilience

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

Go Beyond Life Safety

Link Performance to other Indicators

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

Main authors : ArupSupported by USRC and many others

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

• 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

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

Mobile computing might change how we design

Can we make it safe, sustainable and resilient?

Thank you

design of tall buildings: trends and advancements for...

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