This document discusses recent trends and advancements in performance assessment of high-rise buildings under wind and seismic loads. It covers the evolution of structural engineering from intuition-based design to load-based design. Key challenges like wind and seismic loads are examined. Advancements in modeling and analysis techniques are described, including nonlinear response history analysis and consideration of multiple performance objectives. The importance of calibrating models and validating analysis approaches is emphasized.

1. Recent Trends and Advancement in Performance
Assessment of RC High-Rise Buildings Under Wind
and Seismic Loads
Naveed Anwar, PhD

2. 2 2
Ancient masterpieces were built through intuition and experience
Master builders had freedom to dream and to realize them

3. 33
Beginning of Structural
Engineering
• recognition of the loads,
• and fact that loads have an effect on members and
materials
• and that there is a resistance within materials to resist
the loads effects
• and that there is some relationship between them
1655-1705

4. 4
Increasing
Understanding

5. Main
Challenges !
5
Wind
Earthquake

6. 6
Seismic Load
Wind Load
Depend on
•focus of earthquake
•ground conditions
Depend on
• terrain
• topography of the location
m
ügv
A
Wind force increases as
height increases
▪ 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
Shilpa, 2017

7. 77
Building Industry relies on Codes and Standards
• Codes Specify requirements
• Give acceptable solutions
• Prescribe (detailed) procedures, rules, limits
• (Mostly based on research and experience but not always rational)
Spirit of the code is
to help ensure Public Safety and
provide formal/legal basis for design
decisions
Compliance to
letter of the code is
indented to meet the spirit

8. 8 8
▪ 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 in elastically
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
Shilpa, 2017

9. 9
0
5
10
15
20
25
30
35
40
45
0 10 20 30 40 50 60
The Problem with R Factor
The elastic forces obtained from the
standard RSA procedure
The RSA elastic forces reduced by 𝑅
The inelastic forces obtained from the
NLRHA procedure
The actual reduction in RSA
elastic forces. The “reward”
of making a nonlinear model
The underestimation causing a “false
sense of safety” due to directly reducing
the RSA elastic forces by 𝑅 factor
Story Shear (x106 N)
StoryLevel
• The R factor may vary
from 2 to 8 depending on
definition of structure
type
• R factor could “off” by a
factor of 2 to 4
• Other names for R factor
are Response Factor,
Behavior Factor (q),
Structure Type factor (K)
etc.,
Fawad Najam, 2017

10. 10
The Problem with R (and other) Factors
Reducing each mode with same
factor can underestimate demand
Each Mode undergo different
level of nonlinearity
Modified Modal Superposition
(Priestley and Amaris, 2002)
R applied to only first mode, with
higher modes assumed elastic
Solution
(Rachut, 2013)
Uncoupled modal response history analysis (UMRHA)
R” factor can only
accurately reduce
true demand of the
1st mode

11. 11
Which
hazard
controls the
design?
Does design for wind, effect seismic performance ?

12. 12
Which
Hazard
might
Govern

13. 13
Effect of Assumed R

14. 14
Effect of Assumed R

15. 15
Wind governs
Wind or/and earthquake govern
Earthquake governs

16. 16
Linear-Elastic Wind Design Effects Seismic Performance
16
Elastic Design
Larger Sections for
Stiffness and Motion
Moment Controlled
Flexural
Reinforcement
Larger Mass
Less Ductility
Lower Effective R
Lower Energy
dissipation
Larger Seismic
Demand
Larger Seismic
Demand
Larger Shear due to
Higher Modes
Susceptible to brittle
failure

17. 17
From Prescription to
Performance

18. 1818
Main Structural Performance Concerns
Stability and
integrity
01
Strength and
Servivbility
02
Deformation
03
Drift
04
Ductility
05
Energy
Dissipation
06
Motion
Perception
07

19. 19
The “Arbitrary Factors” in Codes

20. 20
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 ?

21. 21
Capacity Based on “Assumed” Failure Conditions

22. 22
Code
Comparison for
Seismic
Performance
• Compare Performance of buildings designed to
different codes
• ACI 318-14 + ASCE 7-10
• BS 8110-1997 + EURO-8
• EURO-2-2004 + EURO-8
• For low-seismic and high seismic zone
• Manila > Very High
• Bangkok > Low to medium
• All produce different level or performance in different
components !!
Two MS Thesis, 2016 at AIT

23. 23
A Move Towards Performance-based Approach
• Prescriptive Codes restrict
and discourage innovation Objective Requirements
Prescribed
Solution
Objective Requirements
Alternate
Solution
• Performance Based
approach encourages and
liberates innovation

24. 24
Don’t tell them
how to do
Tell them what
is expected
• Make concrete
• 1:2:4, W/C =0.6, Slump=50mm, ….
• Deliver concrete
• 70 MPA, high durability, low shrink, ..

25. 25
Prescriptive Codes – A Shelter and an Impediment
• Public:
• Is my structure safe ?
• Structural Engineer:
• Not sure, but I did follow the “Code”
As long as engineers follow the code, they can be
sheltered by its provisions

26. 26
PBD Approach
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

27. 2727
Explicit Performance Objective in PBD
Performance based design investigates at least two performance objectives explicitly
Service-level
Assessment
Ensure continuity of service for
frequent hazards
(Earthquake having a return period of
about 50)
Collapse-level
Assessment
Ensure Collapse prevention
under extreme hazards
(the largest earthquake with a return
period of 2500 years)
Codes arbitrary implicit
“Design Level”

28. 2828
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

29. 29
Specify Performance Expectance for Hazard Levels
29
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)

30. 30
Designing for different
Hazards in Consistent Manner

31. 31
A shift to Multi Hazard Approach

32. 32
Wind Engineering Through Wind Tunnel Studies
Structural
dynamic
wind loads
& response
study
Structural
dynamic wind
loads &
response study
Facade
pressure
study

33. Earthquake and Wind are Compatible!
33
Site specific Seismic
Hazard Study Site specific Climate
Analysis
Various Earthquake levels
SLE, 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

34. 3434
Possible Way forward
Consider winds of
higher intensity and
longer return
periods
Determine static and
dynamic impacts
through wind tunnel
studies
Incorporate wind
tunnel dynamic
measurements into
dynamic analysis of
structural models
Set appropriate
performance criteria
for motion,
deformation,
strength, ductility,
energy decimation
etc.
Make the Wind PPD
consistent with
Earthquake PBD

35. 3535
Judging Performance Acceptability
• Acceptance criteria are indicators of whether the predicted performance is adequate for
• Local (component based)
• Global (overall structure-based)
• The non-linearity and inelasticity need to be realized and considered

36. 36
Analysis
Procedures
Non-Linear Response History Analysis (NLRHA)
Non-Linear Static Procedure (NSP)
Construction Sequence Analysis
Uncoupled Modal Response History Analysis
(UMRHA)—Chopra and Goel (2002)
Linear Response Spectrum Analysis (LRSA)
Linear Response History Analysis (LRHA)
NeedR

37. 37
Nonlinear Modelling
Fig: Idealized Models of Beam-Column
Elements
NEHRP Seismic Design Technical Brief
Consider Geometric
nonlinearity (P-∆) effects

38. 3838
Modal Analysis ResultsTranslationin
Minor
direction
Translationin
Major
direction
Torsional
• T1=5.32 sec
• 60% in Minor
direction
• T6=1.28 sec
• 18% in Minor
direction
• T9=0.75 sec
• 6.5% in Minor
direction
• T2=4.96 sec
• 66% in Major
direction
• T7=0.81 sec
• 5.2% in Major
direction
• T4=1.56 sec
• 15% in Major
direction
T3=4.12 sec T8=0.65secT5=1.30 sec

39. 39
Base Shear
39
4.1%
2.9%
13.2%
8.7%
3.4%
5.4%
20.0%
14.3%
10.9%
7.0%
0%
5%
10%
15%
20%
25%
X Y
BaseShear%
Along Direction
Base Shear Percentage of Total Weight of Building
Elastic SLE Elastic DBE Wind*1.6 (RWDI)
Elastic MCE Inelastic MCE NLTHA

40. 40
Story Drift
40
0
10
20
30
40
50
-5% 0% 5%
Story
Transient Drift (%)
Transient Drift in X-dir. at MCE Level
ARC
CHY
DAY
ERZ
LCN
ROS
TAB
Average
Avg. Drift
Limit
Max. Drift
Limit
0
10
20
30
40
50
0.0% 0.5% 1.0% 1.5% 2.0%
Story
Residual Drift (%)
Residual Drift in X-dir. at MCE Level
ARC
CHY
DAY
ERZ
LCN
ROS
TAB
Average
Avg. Drift
Limit

41. 41
Shear Walls Performance
41
Strain Gauge (C04)
SW 1-1
-5
5
15
25
35
45
55
-0.006 -0.001 0.004
Story
Axial Strain (mm/mm)
Wall Axial Strain (C04)
ARC
CHY
DAY
ERZ
LCN
ROS
TAB
Average
Steel Yielding
Strain
Strain gauge locations in shear walls

42. 42
Shear Walls
42
-5
5
15
25
35
45
55
-200000 -100000 0 100000 200000
Story
Shear Force (KN)
Shear Wall Shear Demand vs. Capacity (SW1-1)
ARC
CHY
DAY
ERZ
LCN
ROS
TAB
AVERAGE
Capacity
Maximum Limit
Capacity
SW1-1

43. 43
Coupling Beams
43
-10
0
10
20
30
40
50
60
-0.1 -0.05 0 0.05
Story
Rotation (radians)
Link Beam Rotation (LB-1)
ARC
CHY
DAY
ERZ
LCN
ROS
TAB
Average

44. 44
Energy Dissipation
Total dissipated
energy
Dissipated energy from
coupling beams

45. 4545
Diaphragm Transfer Forces
Large diaphragm transfer forces
should be anticipated at offsets
or discontinuities of the vertical
elements of the seismic-force-
resisting system.
(a) Setback in the building profile
(b) Podium level at grade.

46. 46
Soil Structure
Interaction
Modeling
TBI Guidelines
(Practice at AITS)
Practice Research at AIT

47. 47
Innovation
Performance
can not be
achieved in
Isolation

48. 48
Demand
Capacity
(DC Ratio)
• Definition of D/C: It is an index that gives an overall
relationship between affects of load and ability of member to
resists those affects.
• This is a normalized factor that means D/C ratio value of 1
indicates that the capacity (strength, deformation etc) member
is just enough to fulfill the load demand.
• Two types of D/C ratio
➢ Members with brittle behavior D/C is checked by Strength
(Elastic)
➢ Members with ductile behavior D/C is checked by deformation
(Inelastic)
• Total D/C ratio of the member is combined of these two.

49. 49
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

50. Extreme Hazzard Events
should be handled
Consistently
50
Earthquakes, Wind, Fire, Blast,
Progressive Collapse, Impact…

51. 51
Key Focus for Structural Engineers
• Sensing and monitoring of built structures
and calibration of models
• Validation of modeling approaches for
wind and earthquake
• Improved protection, design guidelines
from multiple hazards
• Application of PBD across all hazards

52. 52
Improvements in the
Tools of the Trade
Better analysis and design methods
and software

53. 53
Design Procedures and Software
• Initially, computers were used to
program the procedure we had
• Now, we develop procedures that
are suited for computing

54. 54
Open-source
and
Collaborative
systems

55. 55
Popular Software for Structural Engineers
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

56. 56
Developing Calibrated Models
For materials, sections,
connections, members…

57. A Rational Approach for Developing New Systems
Calibration of with Finite Element Analysis
Full 3D Finite Element Modeling of Typical Structures
Evaluate the Performance Acceptance of Real Sites
Experimental Study and Details

58. Calibration Process
Test Model FE Model
Connection to test

59. 59 59

60. Localization for Site Specific Criteria
FoundationsResponse Spectrum

61. 61
Sensing and Monitoring
Structures
Real Structures as Labs

62. 62
What is
Expected and
can be
Achieved

63. 63
49th Floor
26th Floor
B1
Quick Summary of Event Based on Sensor
Data Analysis
Location of Epicenter
Earthquake Event
Magnitude 6.2
Location 13.99 N 120.67 E
Depth 172.0 Km
Time 2017-08-11, 05:28 UTC
P H I L I P P I N E S
Park Terraces
Towers 1-3

64. 6464
Possible Applications
• Calibration of models using natural periods
• Comparison of Seismic Hazard
• Extraction of Vibration Characteristics from Recorded
Data
• Damage Assessment after the Event
• Detailed Performance-based Seismic Evaluation

65. 65
Making Structures Smarter
In controlling hazards and
response

66. 66
Why we need
“Smart Structures”
• Excitation fluctuates so Demand fluctuates
• But Capacity is constant
• Therefore level of safety is not consistent
• Typically capacity is designed based on “Peak” demand
• What if peak demand never comes > Uneconomical
• What if demand exceeds estimated peak > Un-safe

67. 67
• Smart materials and memory alloys
• Energy Dissipating Systems
• Active or Passive Control Systems
• Health Monitoring Systems
• Data Acquisition System

68. 68
The Wonderful Buckling Restrained Braces - BRB

69. 69 69
Smart structures use smart devices and matersisl
to add some intelligence to adapt, react, adjust,
respond and handle multiple demands, and
levels as and when needed
Help to make the structures safer, specially for
earthquakes and strong winds

70. 70
Bringing in AI and IT
into Structural Design

71. 7171
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

72. 7272
Using AI in Structural Design Process
Architectural
Design
Preliminary
Sizing
Structural
Modeling
Structural
Analysis
Code Based
Design
Performance
Based Design
72
Iterative, computationally intensive and time consuming

74. 74
A move towards Resilience
Recognizing that Purpose and impact
of Structures is More Important than
Structures

75. 7575
Linking Performance to other Indicators
75
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

76. 76Source: Arup, Supported by USRC and many others
Green Buildings Resilient Buildings

77. 77
ARUP

78. 78
Progression of Design Approaches
Wind
Earthquakes

79. 79
Recognizing that Structures
are Critical to Safety,
Resilience and Sustainability
of the Society
A Final Note

80. Thank You
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