naveed anwar, phd progression of structural...
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Naveed Anwar, AIT Solutions
Progression of Structural Design ApproachesNaveed Anwar, PhD
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Colombo 2015
Kathmandu 2016
Bangkok 2016
Singapore 2016
Manila 2016
Oman 2017
Dubai 2017
Dhaka 2014
Yangon 2015
Islamabad2017
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Why this Seminar?
And why are these topics important
Demand and Complexity is Increasing for the Built Environment
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Population Growth is in Developing World
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Source: www.prb.org, volume no. 66, July, 2011.
Less Developed Countries will need more Housing and infrastructure for nearly
2 Billon more people
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(www.un.org)
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Marshall Strabala
Tall Buildings
• Need less space• Need less infrastructure• Need less commutes• Need less façade• Consume less material• Are overall economical• Environmentally
sustainable
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Japan, 4000m Sky Mile Tower, 1700 m JapanDubai City Tower, 2400 m One Dubai Tower, 1008 m
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The Twisting Turning Towers Trend
Source: CTBU Report, 2015
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97%
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Very Tall
(1189)
Super Tall
(115)
Mega Tall(3)
Low Tall
Low Rise
>600 m>300 m>200 m>100 m<50 m
Tall(3852)
>150m
Source: CTBU Report, 2017
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Source: CTBU Report, 2015
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Source: CTBU Report, 2015
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Source: CTBU Report, 2015
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Relatively Tall. Both for public and the professions who design and construct
ProportionSlenderness, in plan and in elevations
Systems and TechnologiesUses something “different” than ordinary buildings
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• Minimize floor depth
• Minimize column size
• Minimize structural cost
• Inclined columns
• Free form
• Unusual requests
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Needs Innovations in Structural Design Approaches
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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?
….. )
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How long do we have
before the building will
collapse in this fire?
- Asks the Fire Chief from the structural
engineer
1974
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https://www.youtube.com/watch?v=FagbC09BO2o
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The Intent of Structural Design is to ensure public safety, minimize damage to built environment, help preserve continuity of life activities…
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Intuitive Design
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Ancient masterpieces were built before the modern approaches
Master builders had freedom to dream and to realize them
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Should design be based on
“Engineering Judgment” and
intuition,
Or
controlled by explicit
computations and, restrictive
limits and rational approaches
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It is by logic we prove, but by
intuition we discover
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Félix Candela
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What a Structural Engineer said !
Hardy Cross, 1885-1959
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Intuitive Design
Code Based Design
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Main Challenges !(specially for Tall Buildings)
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Win
d
Earthquake
Self Weight
Occupancy
and
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Stability
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Strength
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Deformation
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Drift
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Ductility
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Energy Dissipation
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Motion Perception
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Spirit of the code isto help ensure Public Safety and provide formal/legal basis for design decisions
Compliance to letter of the code is indented to meet the spirit
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“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 Baltimorefirst 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.
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UBC, IBC
ACI, PCI, CRSI, ASCE, AISI,
AASHTO
British, CP and BS
Euro-codesChina, USSR,
Japan
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• 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
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Traditional
Design
approach for
Wind and
Earthquake is
different and is
often
in-consistent
and opposing
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Seismic LoadWind Load
Depend on •focus of earthquake
•Shaking intesity
•ground conditions
•Mass and stiffness
distribution
Depend on•Wind speed
• terrain
• topography of the location
• Force increases with height
•Geometry and exposed area
m
ügv
A
Excitation is an applied displacement
at the base
force will be distributed along interior
and exterior lateral load resisting
elements
Excitation is an applied pressure or
force on the facade
force will act mainly on exterior
frames then transferred to floor
diaphragms
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For most buildings, dynamic wind response may
be neglected
Gust factor approach predict dynamic
response of buildings with reasonable accuracy
Structures are designed to respond elastically
under factored loads
Structures are designed to respond inelastically
under factored loads
it is not economically feasible to design structures
to respond elastically to earthquake ground
motion
Design for Seismic EffectsDesign for Wind Load
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Intuitive Design
Code Based Design
Performance Based Design
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Earthquake
Wind
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• Lack of explicit performance in design codes is
primary motivation for performance based
design
• Performance based methods require the
designer to assess how a building is likely
perform extreme events and their correct
application will help to identify unsafe designs.
• Enables arbitrary restrictions to be lifted and
provides scope for the development of
innovative, safer and more cost-effective
solutions
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Based on FEMA 451 B
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Structural Displacement
Lo
adin
g S
ever
ity
Resta
urant
Resta
urant
Resta
uran
t
Ha
zard
Vulnerability
Consequences
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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)
Code’s arbitrary “Design Level”
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Intuitive Design
Code Based Design
Performance Based Design
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Wind
Earthquake
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Earthquake and Wind PBD are Compatible!
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Site specific Seismic Hazard Study
Site specific Climate Analysis
Various Earthquake levelsSLE, DBE, MCE etc
Various Wind Return period and Velocities
Hazard Response Spectrum
Wind Force in Frequency Domain
Ground Motion Time History
Wind Tunnel Pressure in Time Domain
Earthquake Wind
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Intuitive Design
Code Based Design
Performance Based Design
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Wind
Earthquake
Is this acceptable?Even though it satisfies CBD and may even satisfy PBD
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
Design Approaches
Intuitive Design
Code Based Design
Performance Based Design
Consequence and Risk Based Design
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Wind
Earthquake
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).
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The trigger of an event is not important, the consequences of an event are
Risk Based Design Process
Safety Studies (Probability and
Consequence Analysis)
Risk Quantification and modeling
Safety Critical Element
Design Accidental
Loads
Structure Design
Verification
Extreme Events
should be handled
Consistently
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Earthquakes, Wind, Blast, Progressive Collapse, Impact
What Next: What is still missing?
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Design Approaches
Intuitive Design
Code Based Design
Performance Based Design
Consequence and Risk Based Design
Resilience Based Design
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Green Buildings Resilient Buildings
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Main authors : ArupSupported by USRC and many others
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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
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Economic Loses
Loss of Community and Culture
Loss of Quality of
Life
Go Beyond Life Safety
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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 Highest
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ARUP
About Related work at AIT
Related work at
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Asian
Institute of
Technology
(AIT)
• Established in Bangkok in 1959
• Leading regional postgraduate
institution
•Actively working with public and
private sector in the region
•Collaborating with some of the top
universities in the world
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Professional Education Integrated Solutions
ResearchAcademics
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What is being done at AIT
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Structural LabShake table, Cyclic
Actuator, strong floor
Teaching, Research Tall Buildings, Wind
and Earthquake Engineering
Practical Experience of over 100 PBD
Projects
Wind Tunnel Lab
Development and application of Integrated PBD and RSBD for Wind and Earthquake
CSiSoftware Developer
PartnersStructural Engineers
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“Building upon AIT schools,
labs, research centers and
alumni resources to advance
technological development
in the region”
Mission
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Tools: How to design efficiently?
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• Initially, computers were used to
program the procedure we had
• Now, we develop procedures that
are suited for computing
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Integrated 3D Bridge Design Software
Integrated Software for Structural Analysis and Design
Integrated Analysis, Design and Drafting of Building Systems
Integrated Design of Flat Slabs, Foundation Mats and Spread Footings
Nonlinear Analysis and Performance Assessment for 3D Structures
Design of Simple and Complex Reinforced Concrete Columns
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Should design be based on
“Engineering Judgment” and
intuition,
Or
controlled by explicit
computations and, restrictive
limits and rational approaches
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Architectural Design
Preliminary Sizing
Structural Modeling
Structural Analysis
Code Based Design
Performance Based Design
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Heuristic Approach to Quick Design and Response Prediction of Tall Buildings
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More explicit way to define and measure performance
Obtain consistency between EQ and Wind design and performance
Economy and cost effective design for both wind and EQ
Enhanced overall performance and reliability of buildings
Accelerate innovations in the structural design process
Advance the state of the art to integrated resilience based design
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Thank you
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