7th Annual Vertical Cities, 7th – 9th March 2018, Bangkok, Thailand

1. Cost Effective Structural Configurations
For Tall Buildings
Naveed Anwar, PhD
Executive Director, AIT Solutions
Affiliated Faculty, Structural Engineering
Director, ACECOMS

2. 2
AIT Solutions at Asian Institute of Technology

3. 3
The Talk
• Conceptualizations of structural configuration
systems, together with various application
scenarios and efficiencies
• Delving into the application of outriggers,
dampers, BRB, transfer systems, etc.
• Quick design decision system based on Machine
Learning (ML) and Artificial Intelligence (AI)
Academics + Research + Projects + Tools

4. 4
Focus of the Talk – “Tallness Range”
Low
Rise
>500 m>300 m>200 m>100 m<50 m >150m
Source: CTBU Report, 2018

5. 5 5
100
200
meters
PBD of 100+ Tall Buildings
300
System Development, Performance Based Evaluation, Value Engineering

6. Conceptualizations of structural configuration and systems
The basic concepts and considerations for developing efficient structural system

7. 7
Main Challenges !
7
Wind
Earthquake
Gravity
emaze.com
Optimizing for one, may de-optimize for others !

8. 8
Main Structural Concerns
Stability
01
Strength
02
Deformation
03
Drift
04
Ductility
05
Energy
Dissipation
06
Motion
Perception
07

9. 9
4 Commandments for Lateral Load Systems
Resist overturning forces
due to lateral loads by
using vertical elements
placed as far apart as
possible
1
Channel gravity loads to
those vertical elements
resisting overturning
forces
2
Link these vertical
elements together with
shear-resisting structural
elements with minimum
shear lag to activate
entire perimeter of the
building
3
Axial loaded members in
compression to resist
overturning forces
4

10. 10
Choosing the
“Right” Gravity Load
Resisting System
• Direct Load Transfer Systems
• Flat Slab and Flat Plate
• Beam-Slab
• Waffle Slab
• Wall Joist
• Indirect Load Transfer System
• Beam, Slab
• Girder, Beam, Slab
• Girder, Joist
• Materials
• Steel/ Composite Deck
• Reinforced Concrete
• Post-tensioned slab systems
Least weight
Fast Construction cycle
Least structural depth

11. 11
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
üg
v
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

12. 12
▪ 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

13. 13
The Significance of Modal Response

14. 14
Effect of Modes on Story Moment
14

15. 15
Effect of Modes on Story Shear
15

16. Efficiency of Structural Configurations and Systems
The basic concepts and considerations for developing efficient structural system

17. 17
Cost and Performance
• Bigger, taller, complex forms, but Lighter, smaller, thinner structural elements
• High performance, but Lower cost

18. 18
Some Structural Efficiency Indicators
Structural
Volume/Building
Volume
• Concrete
Volume/Total
Volume
• Steel Volume/Total
Volume
Structural Area/Floor
Area
• Shear Walls
• Columns
Reinforcement
Ratios
• Rebar
Weight/Concrete
Volume
• Rebar Weight/Floor
Area
Demand/Capacity
• Ductility
• Strength

19. 19
Configuration Effects
K: 1+1 = 2 K: 1 +1 =8
1 + 1 2

20. 20
Basic Structural System Configurations
K=1 K=1.6 K=0.8 K=3.5 K=4

21. 21
Building

22. 22
Beams and
Columns

23. 23
Shear Walls

24. 24
Performance Based Design and Evaluation
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
Free to choose solutions, but
ensure 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

25. 25
Explicitly Evaluate Performance for Expected Hazard Levels
25
Acceptance Criteria for Maximum Considered Earthquake
(MCE)
Item Value
Peak transient drift
(TBI, Page 71) , (LATBSDC,
Page 40)
Maximum of mean values shall not
exceed 3%.
Maximum drift shall not exceed 4.5%.
Residual drift
(TBI, Page 71) , (LATBSDC,
Page 40)
Maximum of mean values shall not
exceed 1%.
Maximum drift shall not exceed 1.5%.
Coupling beam inelastic
rotation
≤ASCE 41-13 limits
Column Inelastic Rotation ≤ASCE 41-13 limits
Shear wall reinforcement axial
strain
≤0.05 in tension and ≤0.02 in
compression
Shear wall shear Remain elastic. (Check for 1.5 times
mean value)
Girder inelastic rotation ≤ASCE 41-13 limits
Girders shear Remain elastic.
Force
Structural
Displacement
Immediate
Occupancy
(IO)
Life
Safety
(LS)
Collapse
Prevention
(CP)

26. 26
Nonlinear and Analysis for PBD

27. 27
Cost Effectiveness > Utilization Ratio
• Utilization Ratio
• Compare, What is
Needed against What is
Required
• One measure
• The Demand/ Capacity
Ratio (D/C)
Demand/ Capacity
Columns
No. %
D/C<0.5 178 16%
0.5<D/C<0.7 534 49%
0.7<D/C<1 346 31%
1<D/C<1.5 30 3%
1.5<D/C<2.5 12 1%
D/C>2.5 0 0%
Total 1100 100.00%
Ideal
Not Cost
Effective
Not Safe

28. A Quick Look at Some Structural Configurations
Some case studies and research

29. 29
Wall + Column Area
Max 11, Mean 6, Min 2
230 m, 11% 215m, 5%205m, 7%

30. 30
Wall Only Systems

31. 31
Un-coupled Distributed Shear Walls

32. 32
Frame and Shear Walls

33. 33
Core Wall Only

34. 34
Coupled Shear Walls

35. 35
Distributed Cores

36. 36
Just Core Supported

37. Outriggers, Dampers, BRB, Transfer Systems
How large size structural members can be used to improve structural efficiancy

38. 38
Outrigger Effects
K: 1+1 = 2 K: 1 +1 =8
1 + 1 2

39. 39
Effectiveness of Outriggers
Reduce the natural period – Good forwent responseReduce
Reduce top displacementReduce
Reduce driftReduce
Reduce moment in shear wallsReduce
Follow the All 4 CommandmentsFollow
Do not reduce shear in shear wallsDo not reduce
Need space to implementNeed

40. 40
Real Vs Virtual Outriggers
• Virtual Outriggers are more acceptable” from
architectural planning and circulation viewpoint
• They are nearly as effective as “real” outriggers
Direct or “real” Outriggers In-direct or “viryual” Outriggers

41. 41
Adding Belts
• More even distribution
of axial loads on
perimeter columns
• Reduces possibility of
tension in columns or
foundatons
• Provides virtual
outrigger effect in both
directon

42. 42
Buckling Restraint Braces, BRB

43. 43
BRB – An efficient Outrigger and Damper

44. 44
N1-S1Core Only N1-S2 N1-S3 N2-S3 N3-S3
Flag Walls – an Alternative to Outriggers

45. 45
Core Only Config 1 Config 2 Config 3 Config 4 Config 5
Flag Walls – an Alternative to Outriggers

46. 46
Staggered Walls as Outriggers

47. 47
Isolated Flag Walls

48. 48
Flag Walls and Coupled Walls as Outriggers

49. Predicting Design Using Machine Learning

50. 50
A Swing Towards the AI
• Rich Pictures
• Analytical Hierarchy Process (AHP)
• Artificial Neural Networks (ANN)
• Genetic Algorithms (GA)
• Expert Systems (ES)
• Machine learning (ML)
• Fuzzy Logic
• Deep Thinking
• Big Data and Data Mining
50

51. 51
Using AI in Structural Design Process
Architectural
Design
Preliminary
Sizing
Structural
Modeling
Structural
Analysis
Code Based
Design
Performance
Based Design
51
Iterative, computationally intensive and time consuming

52. 52
Our Approach

53. 53

54. 54
The Overall PROCESS

55. 55
A Concluding
Note
Engineering for
performance, resource and
cost efficiency and
effectiveness leads to
sustainable design

56. Thank you!
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