1. Dr. Naveed Anwar
Executive Director, AIT Consulting
Affiliated Faculty, Structural Engineering
Director, ACECOMS
Design of Tall Buildings
AIT Hybrid Learning System

2. Dr. Naveed Anwar
Executive Director, AIT Consulting
Affiliated Faculty, Structural Engineering
Director, ACECOMS
Lecture 9: Structural Analysis
for Lateral Loads
Design of Tall Buildings

3. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
• Analysis for Earthquake
– Basic Elements of Seismology
– The Seismic Analysis Problem
– Forces generated by Earthquakes
– Vertical and Horizontal Regularity
– Seismic Analysis Methods
• Analysis Using Equivalent Static
Load
• Analysis Using Response Spectrum
• Analysis Using Acceleration Time
History
– Capacity Design Approach
– Earthquake Analysis using ETABS
and SAP 2000
Lecture Contents
• Analysis for Wind
– The Wind Analysis Problem
– Bluff Body Aerodynamics
– Wind Effects on Tall Buildings
– Analysis Using Equivalent Static
Load
– Combining Response for Member
Design
3

4. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Analysis for Earthquake
4

5. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Basic Elements of Seismology
5

6. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
The Earth
Inside the EarthSource: Murty (2004)
6

7. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Dip Slip (normal or thrust) Strike Slip (right or left lateral)
Four Basic Types of Faults
A fault is a fracture along which the blocks of
crust on either side have moved relative to one
another parallel to the fracture.
Source: Murty (2004)
7

8. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Theory of Continental Drift
An earthquake is caused by the
rebound of elastically strained rock.
Elastic Rebound Theory
Source: httap://www.seismo.unr.edu
8

9. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Plate Tectonics
Source: Murty (2004)
9

10. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Convergence plate boundary: Subduction zone, etc.
Divergence plate boundary: Plates diverges at mid-ocean ridges
Transform fault: Plates move laterally past each other
Earth’s 14 Lithospheric Plates
and Their Movements
Source: Murty (2004)
10
Earth’s Changing Landscape

11. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Seismic Waves
Body Wave
Surface Wave
11

12. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 12

13. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 13
Arrival of Seismic Waves at a Site
Source: Murty (2004)

14. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 14
Basic Terminology
Reducing illumination with distance
from an electric bulb
Electric Bulb Analogy
Source: Murty (2004)

15. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Classifying the Earthquakes
Terminology used to
define earthquake
Maximum Credible Earthquake (MCE)
Maximum Design Earthquake (MDE)
Safe Shutdown Earthquake (SSE)
Contingency Level Earthquake (CLE)
Ductility Level Earthquake (DLE)
Operating Basis Earthquake (OBE)
Maximum Probable Earthquake (MPE)
Strength Level Earthquake (SLE)
15

16. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 16
• Maximum Credible Earthquake (MCE)
– Earthquake associated with specific seismotectonic structures, source areas or
provinces that would cause the most severe vibratory ground motion or
foundation dislocation capable of being produced at the site under the
currently known tectonic framework
– Determined by judgment based on all known regional and local geological and
seismological data
– Little regard is given to its probability of occurrence, which may vary from less
than a hundred to several tens of thousands of years
Classifying the Earthquake

17. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 17
• Maximum Design Earthquake (MDE)
– Represents the maximum level of ground motion for which the structure
should be designed or analyzed.
• Safe Shutdown Earthquake (SSE)
– The maximum earthquake potential, for which certain structures, systems, and
components, important to safety, are designed to sustain and remain
functional (used in the design of nuclear power plants)
• Contingency Level Earthquake (CLE)
– Earthquake that produces motion with a 10% probability of exceedance in 50
years. For this event, the structure may suffer damage, however, life safety is
protected.
Classifying the Earthquake

18. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 18
• Operating Basis Earthquake (OBE)
– EQ for which the structure is designed to resist and remain operational.
– The OBE is usually taken as an:
• EQ producing the maximum motions at the site once in 110 years
(recurrence interval)
• EQ with half the peak acceleration of SSE
• EQ that produces motion with a 50% probability of exceedances in 50
years
Classifying the Earthquake

19. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 19
• Maximum Probable Earthquake (MPE)
– The maximum EQ that is likely to occur during a 100 year interval.
• Strength Level Earthquake (SLE)
– The maximum earthquake that is likely to occur during a 200 year interval
– This earthquake is not anticipated to induce significant damage or inelastic
response in the structural elements
Classifying the Earthquake

20. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
The Seismic Analysis Problem
20

21. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
The Basic Equilibrium Equations
• Linear-Static Elastic
• Linear-Dynamic Elastic
• Nonlinear - Static Elastic OR Inelastic
• Nonlinear-Dynamic Elastic OR Inelastic
1FKu 
2)()()()( tFtKutuCtuM  
4)()()()()( tFtFtKutuCtuM NL  
3FFKu NL 
21

22. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Linear and Nonlinear
• Linear, Static and Dynamic
• Nonlinear, Static and Dynamic
Non Linear Equilibrium
FKu 
)()()()( tFtKutuCtuM  
)()()()()( tFtFtKutuCtuM NL  
FFKu NL 
22

23. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Basic Analysis Types
Excitation Structure Response Basic Analysis Type
Static Elastic Linear
Linear-Elastic-
Static Analysis
Static Elastic Nonlinear
Nonlinear-Elastic-
Static Analysis
Static Inelastic Linear
Linear-Inelastic-
Static Analysis
Static Inelastic Nonlinear
Nonlinear-Inelastic-
Static Analysis
Dynamic Elastic Linear
Linear-Elastic-
Dynamic Analysis
Dynamic Elastic Nonlinear
Nonlinear-Elastic-
Dynamic Analysis
Dynamic Inelastic Linear
Linear-Inelastic-
Dynamic Analysis
Dynamic Inelastic Nonlinear
Nonlinear-Inelastic-
Dynamic Analysis
23

24. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 24
• Non-linear Analysis
– P-Delta Analysis
– Buckling Analysis
– Static Pushover Analysis
– Fast Non-Linear Analysis (FNA)
– Large Displacement Analysis
• Dynamic Analysis
– Free Vibration and Modal Analysis
– Response Spectrum Analysis
– Steady State Dynamic Analysis
Special Analysis Types

25. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Comprehensive Equilibrium Equation
)()()()()( tFtFtKutuCtuM NL  
• Cover all Static, Dynamic, Elastic, Non Elastic, Damped, Un-damped,
Linear, Non-Linear cases and their combinations
• Handles response for:
– Basic Dead and Live Loads
– Seismic, Wind, Vibration and Fire Analysis
25

26. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Comprehensive Equilibrium Equation
FFKuuCuM NL  
Damping-Velocity
Mass-Acceleration Stiffness-Displacement
Nonlinearity
External Force
KuuCuM  
The basic variable is displacement and its derivatives
26

27. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Static Part
Dynamic Part
Static and Dynamic
FFKuuCuM NL  
KuuCuM  
27

28. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 28
• Static Excitation
– When the excitation (load) does not vary rapidly with time
– When the load can be assumed to be applied “slowly”
• Dynamic Excitation
– When the excitation varies rapidly with time
– When the “inertial force” becomes significant
• Most Real Excitation are Dynamic but are considered “Quasi Static”
• Most Dynamic Excitation can be converted to “Equivalent Static Loads”
Static versus Dynamic

29. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Linear and Non-Linear
FFKuuCuM NL  
Linear Part
Non-Linear Part
KuuCuM  
29

30. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
The Structure Stiffness - K
Section Stiffness
Member Stiffness
Structure Stiffness
Material Stiffness
Cross-section Geometry
Member Geometry
Structure Geometry
Linear
Non-Linear
30

31. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Seismic Analysis
FFKuuCuM NL  
Time History Analysis
0 KuuM 
EQNL FFKu 
Free Vibration
Pushover
Analysis
EQFKu 
Equivalent
Static Analysis
EQFKu 
Response Spectrums
Response Spectrum
Analysis
Acceleration Records
guMKuuCuM  
31

32. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
A SDOF System
32
Idealized SDOF system
Un-damped free vibrations of SDOF system Damped free vibrations of SDOF system

33. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
A MDOF System
33
Representation of a multi-
mass system by a single-
mass system:
(a) fundamental mode of a
multi-mass system and
(b) equivalent single-mass
system.

34. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Forces Generated by
Earthquakes
34

35. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 35
Schematic Representation of Seismic
Forces

36. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 36
Concept of 100% g (1g)
Linear Viscous Damper

37. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Force Reversal
37
Bilinear Force–displacement Hysteresis Loop

38. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Inertial Forces
38
Effect of Inertia in a building when
shaken at its base
Flow of seismic inertia forces
through all structural
components
Source: Murty, (2004)
Inertia force and relative
motion within a building

39. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 39
The natural period values are only indicative; depending on
actual properties of the structure, natural period may vary
considerably.
Fundamental natural periods of
structures differ over a large
range. Source: Murty (2004)
Free vibration
response of a
building: the
back-and-
forth motion is
periodic.

40. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 40
Different Buildings Respond Differently
to Same Ground Vibration
Building Behavior during
Earthquakes
Source: Murty (2004)

41. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Vertical and Horizontal
Regularity
41

42. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 42
Simple plan shape buildings do well
during earthquakes
Buildings with one of their overall sizes much larger or
much smaller than the other two, do not perform well
during earthquakes
Identical vertical members placed
uniformly in plan of building cause all
points on the floor to move by the same
amount.
Source: Murty (2004)

43. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 43
Sudden deviations in load transfer path along the height lead to poor
performance of buildings. Source: Murty (2004)

44. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 44
Rope swings and buildings: both swing back-
and-forth when shaken horizontally. The former
are hung from the top, while the latter are
raised from the ground.
Even if vertical members are placed uniformly in
plan of building, more mass on one side causes
the floors to twist.
Source: Murty (2004)

45. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 45
Buildings have unequal vertical
members; they cause the building
to twist about a vertical axis
Source: Murty (2004)

46. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 46
Vertical members of buildings that
move more horizontally sustain
more damage
Pounding can occur between
adjoining buildings due to
horizontal vibrations of the two
buildings
Source: Murty (2004)

47. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
This is what earthquakes do … (Click to watch)
47

48. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
The Tragic Side…
48
On 8 October 2005, an earthquake of
magnitude 7.6 hit Islamabad,
Pakistan, killing 30, 000 and seriously
injuring another 60, 000 people.
Some structures collapsed next to
others of the same age that
remained intact.
This zone was classified as to be
considered as only moderate. UBC 97
was applied by private consultants.
Courtesy: L. A. Prieto Portar (2008), University of Florida

49. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Kashmir Earthquake (Oct 8, 2005)
Magnitude = 7.7
Death Toll > 80,000
49

50. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Haiti Earthquake (2010)
Magnitude = 7.0
Death Toll: 100,000 ~ 200,000
50

51. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 51
Upper storeys of open ground
storey buildings move together as
a single block – such buildings are
like inverted pendulums.
Soft Story Mechanism
Source: Murty (2004)

52. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 52
Open ground storey building - assumptions made in current design practice are
not consistent with the actual structure.
Source: Murty (2004)

53. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Soft Story Failures
53

54. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Seismic Analysis
Methods
54

55. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 55
• Linear Static Procedures
– Equivalent Static Analysis
• Nonlinear Static Procedures
– Capacity Spectrum Method
– Displacement Coefficient Method
– Various Other Pushover Analysis Methods
• Linear Dynamic Procedures
– Response Spectrum Analysis
– Linear Response History Analysis
• Nonlinear Dynamic Procedures
– Nonlinear Response History Analysis
Seismic Analysis Procedures

56. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 56
• Study the Geology of the Region
• Study the Past EQ Records
• Prepare General Soil Profile
• Potential Site Amplification of Ground Motion
• Estimation of Soil Shear Wave Velocity (SWV)
• Soil Classification Based on SWV
• Estimation of Soil Dynamic Properties
• Collect Information about Existing Buildings
• Estimate/Measure Time Period of Buildings
• Classify the Buildings in Terms of Risk
• Develop Design Response Spectra
Seismic Hazard Analysis Process

57. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Seismic Hazard Curve
Seismic hazard curve for Bangkok (Warnitchai & Lisantono, 1996)
57

58. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Typical Dynamic Analysis
Typical Dynamic Analysis
Free Vibration Response
Response to Harmonic Forces
Response to Periodical
Loading
Response to Impulse Loading
Ambient Vibration Response
Response to
Direct Dynamic Force
Response to
Earthquake Excitation
58

59. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 59
• Definition
– Natural vibration of a structure released from initial condition and subjected
to no external load or damping
• Main governing equation - Eigenvalue Problem
• Solution gives
– Natural Frequencies
– Associated mode shapes
– An insight into the dynamic behavior and response of the
structure
Free Vibration Analysis
         tt
tt
PuKucuM 












 

60. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Mode Shapes
• A mode shape is a set of relative (not absolute) nodal displacement for a particular
mode of free vibration for a specific natural frequency
• There are as many modes as there are DOF in the system
• Not all of the modes are significant
• Local modes may disrupt the modal mass participation
60

61. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
The Modal Analysis
• The modal analysis determines the inherent natural frequencies of vibration
• Each natural frequency is related to a time period and a mode shape
• Time Period is the time it takes to complete one cycle of vibration
• The Mode Shape is normalized deformation pattern
• The number of Modes is typically equal to the number of Degrees of Freedom
• The Time Period and Mode Shapes are inherent properties of the structure
and do not depend on the applied loads
61

62. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
The Modal Analysis
• The Modal Analysis should be run before applying loads any other analysis to check
the model and to understand the response of the structure.
• Modal analysis is precursor to most types of analysis including Response Spectrum,
Time History, Push-over analysis, etc.
• Modal analysis is a useful tool even if full Dynamic Analysis is not performed.
• Modal analysis is easy to run and is fun to watch when animated.
62

63. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 63
• The Time Period and Mode Shapes, together with animation
immediately exhibit the strengths and weaknesses of the structure.
• Modal analysis can be used to check the accuracy of the structural model
– The Time Period should be within reasonable range,
• (Ex: 0.1 x number of stories seconds)
– The disconnected members are identified
– Local modes are identified that may need suppression
Application of Modal Analysis

64. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 64
• The symmetry of the structure can be determined
– For doubly symmetrical buildings, generally the first two modes are
translational and the third mode is rotational
– If the first mode is rotational, the structural is un-symmetrical
• The resonance with the applied loads or excitation can be avoided
– The natural frequency of the structure should not be close to excitation
frequency
Application of Modal Analysis

65. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Modal Analysis Results
65
Translationin
Minordirection
TranslationinMajor
direction
Torsional
• T1=5.32 sec
• 60% in
Minor
direction
• T6=1.28 sec
• 18% in
Minor
direction
• T9=5.32 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

66. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Eccentric and Concentric Response
Mode-1 Mode-2 Mode-3
Symmetrical Mass
and Stiffness
Unsymmetrical Mass
and Stiffness
66

67. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
• Damper is an energy absorbing
element
• Viscous damper is the most common
• Energy is lost by heat, friction,
damages, etc.
• Free vibration of a damped system
dies out gradually
Damped System
67

68. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Damped Dynamic Response
68
Easy to Remember: 1, 2, 4 Cycle for 10, 5, 2.5
0
1
2
3
4
5
6
7
0.02 0.04 0.06 0.08 0.1
NoofCyclestoReducePeakAmplitudeby50%
Damping Ratio
Effect of Damping (Approximate)

69. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Basic Dynamic for Ground Motion
g
g
g
g
uuuu
umumumum
umkuucum
mc
m
k
ummgumF
Fkuucum











2
2
2
2
2;



69

70. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
• The input Variables are ground
acceleration, damping ratio and
circular frequency
• The final unknown is displacement
(and its derivatives)
Ground Motion
guuuu   2
2 
70

71. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Modal Displacements
71

72. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 72
• Code based, Equivalent Static Methods
– Uses single mode, single DOF approach
• Modal Analysis
– Determines the basic, inherent dynamic response indicators
• Response Spectrum Methods
– Linear, using modal combination and “Response Reduction Factor”
– Nonlinear Static Pushover Methods
• Time History Methods
– Linear Time History method and “Response Reduction Factor”
– Nonlinear Time History Analysis
Estimating Seismic Response

73. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 73
Analysis Using Equivalent Static
Load

74. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 74
• Model Code
– IBC 2000
• International Building Codes
• NEHRP Provisions
• FEMA 368-369 Provisions
• Incorporates most recent (1996) USGS Hazard Maps
• Guidelines
– ATC -40
• Applied Technology Council
– FEMA
• Federal Emergency Management Agency
Model Codes and Guidelines

75. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
The Basic Notion
• Convert the Seismic Excitation to an “Equivalent Static Force” applied at the base of
the building, called the Base Shear. Then Distribute the Base Shear to various parts
of the Building by using:
V = W C ( from F = m a)
• This formula is based on the assumption that the structure will undergo several
cycles of inelastic deformation and energy dissipation without collapse. Force and
displacements in the structure are derived assuming linear behavior.
75

76. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 76
• The old equation: V = (Z K C S I) W
• The new equation:
– I = Importance factor, for a specific occupancy category, from UBC Table
16-K
– Cv = Velocity based ground response coefficient, for a specific seismic zone
and soil profile, from UBC Table 16-R
– R = Response modification factor, for a specific structural system, from UBC
Table 16-N
– T = Fundamental, period of vibration, from UBC Formula (30-8) or (30-10)
The UBC-97 Form of Equation
RT
ICv
s
s
C
WCV



77. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 77
• Maximum Inelastic Displacement (Eq. 30-17)
– ∆M = 0.7 R ∆s
– ∆M = maximum inelastic displacement
– R = overstrength factor
– ∆s = design level displacement by design seismic forces
• Drift Limit
– For structures having a time period of < 0.7s, Drift limit = 0.025 x story height
– For structures having a time period of ≥ 0.7s, Drift limit = 0.02 x story height
– Actual time period calculated by Method B shall be used to calculate the
design lateral force for story drift and neglect the 30% or 40% limitations in
Section 1630.2.2.
– Design base shear minimum limit formula (30-6) will also be neglected.
Inelastic Displacement and Drift (UBC 97)

78. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
The IBC-06 Form of Equation
CsWV 







E
DS
S
I
R
S
C
MSDS SS
3
2
 SaMS SFS 
Fa = Site coefficient short period , Table 1615.1.2(1)
Ss = Spectral accelerations for short periods, Maps
R = The response modification factor, Table 1617.6
T
I
R
S
C
E
DI
S







EDSS ISC 044.0







E
S
I
R
S
C 15.0
IE = The occupancy importance factor, Section 1616.2
Cs does not
need to be
greater than
T = Fundamental period (in seconds) of the structure
11
3
2
MD SS  11 SFS VM 
FV = Site coefficient, 1 sec period, Table 1615.1.2(2).
S1 = Spectral accelerations for a 1-second period, Maps
Cs must be greater than
78

79. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 79
• W includes:
– In areas used for storage, a minimum of 25% of the reduced floor live load
(floor live load in public garages and open parking structures does not have to
be included.
– Where an allowance for partition weight or a minimum weight of 50 kg/m2 of
floor area, whichever is greater.
– Total operating weight of permanent equipment.
– 20 % of flat roof snow load where the flat roof snow load exceeds 150 kg/m2
The IBC-06 Form of Equation

80. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
• R is dependent on structural system and ranges from 1.5 to 8 (bad to good)
• Fa is site modification for short period spectrum and ranges from 0.8 to 2.5 (good
to bad)
• Fv is a site modification for 1 sec period spectrum and ranges from 0.8 to 3.5 (good
to bad)
• I ranges from 1.0 to 1.5 (Normal to important)
80
The IBC-06 Form of Equation

81. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
IBC-2006: General Procedure
• Maximum Considered Earthquake (MCE) based on 2005 USGS probabilistic hazard
maps
• Deterministic limits used in high seismicity areas where the hazard can be driven by
tails of distributions
• Hazard maps provide spectral accelerations for
– T = 0.2 Sec called Ss
– T= 1.0 Sec called S1
• Local soil conditions considered using site coefficients
– Fa for short duration
– Fv for longer duration
• Develop the design spectrum using “S” and ‘F
81

82. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
The Overall Procedure
• Step 1: Determine Seismic Zone Factor, Z
• Step 2: Determine Seismic Source Type
• Step 3: Determine Near Source Factor
• Step 4: Determine Soil Profile Type
• Step 5: Determine Ground Response Coefficients, Ca and Cv
• Step 6: Determine Fundamental period, T
82

83. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
The Overall Procedure
• Step7: Classify the Structural System and determine the Response Modification
Factor, R
• Step 8: Determine the Occupancy Categories and Importance Factor, I
• Step 9: Determine the Seismic Response Coefficient, Cs
• Step 10: Determine the Base Shear
• Step 11: Vertical Distribution of Base Shear into Lateral Forces
83

84. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Equivalent Lateral Load Procedure
• Calculation of seismic response coefficient ,
where







I
R
S
C DS
S
factoronmodificatiresponseTheR
periodshortatparameteronacceleratiresponsespectraldesignDSS
factorimportanceoccupancyTheI
84

85. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Equivalent Lateral Load Procedure
• Upper limit of seismic response coefficient,
• Lower limit of seismic response coefficient,
R = response modification factor
SD1 = design spectral response acceleration parameter at a period of 1s
TL = long-period transition period
T = fundamental period of building
I = importance factor
L
D
S TT
I
R
T
S
C 






 for1
L
LD
S TT
I
R
T
TS
C 






 for
2
1
01.0SC
85

86. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Equivalent Lateral Load Procedure
• Buildings and structure for which the 1-second spectral response, S1 , is
equal to or greater than 0.6 g, the value of the seismic response
coefficient, Cs , shall not be taken as less than:
R = response modification factor
S1 = spectral response acceleration parameter at a period of 1s
I = importance factor
IR
S
CS
/
5.0 1

86

87. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Equivalent Lateral Load Procedure
• Computing Time Period, T:
– The fundamental period of the building, T , in the direction under
consideration shall be established using the structural properties and
deformational characteristics of the resisting elements in a properly
substantiated analysis
• Or
– Shall be taken as the approximate fundamental period, Ta. The calculated
fundamental period, T, shall not exceed the product of the coefficient for upper
limit on calculation period, Cu, and the approximate fundamental period , Ta.
87

88. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Equivalent Lateral Load Procedure
• Approximate fundamental period
N = number of stories
h = height in feet
stories)12exceedingnot(buildings1.0 NTa 
x
nt hCTa 
88

89. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Equivalent Lateral Load Procedure
• Vertical distribution of seismic forces:
• The lateral force, (kip or kN) , induced at any level:
where
– Cvx =Vertical distribution factor.
– k = A distribution exponent related to the buildings period as follows:
• For buildings having a period of 0.5 second or less, k = 1
• For buildings having a period of 2.5 seconds or more, k = 2
• For building having a period between 0.5 and 2.5 seconds or more, k shall be 2 or
shall be determined by linear interpolation
VCF vxx 

 n
i
k
ii
k
xx
vx
hw
hw
C
1
89

90. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Hazard Maps for Determining Ss, S1
90

91. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 91
• Adjust Maximum Considered
Earthquake (MCE) values of Ss
and S1 for local site effects
– SMs = Fa x Ss
– SM1 = Fv x S1
• Calculate the spectral
design values
– SDS = 2/3 x SMS
– SD1 = 2/3 x SM1
Design Spectral Values

92. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Site Classification Characteristics
• Soil conditions at the site should be determined.
• They modify the ground motion
• Based on the site soil properties, the site shall be classified as either Site Class A, B,
C, D, E or F in accordance with Table 1613.5.2
• When the soil properties are not known in sufficient detail to determine the site
class, Site Class D shall be used unless the building official or geotechnical data
determines that Site Class E or F soil is likely to be present at the site
92

93. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Site Classification Characteristics
93

94. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Site Coefficients
• To adjust maximum considered earthquake spectral response acceleration
according to soil conditions
SMS =Fa Ss
SM1 = Fv S1
94

95. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Site Coefficients
95

96. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Seismic Design Category
• The structure must be assigned a seismic design category.
• Determines the permissible structural systems
• Determines limitations on height and irregularity.
• Determines those components of the structure that must be designed for seismic
• loads, and the types of analysis required.
• The seismic design categories, designated A through F
• They depend on the seismic use group and the design spectral acceleration
coefficients, SDS and SD1. The structure is assigned the more severe of the two
values taken from these tables
96

97. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Seismic Design Category
97

98. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 98
• Seismic Design Category are used to select:
– Type of analysis
• Very Simplified
• Equivalent Lateral Load Procedure
• Response Spectrum
• Time-history
– Type of design and detailing
• Special Detailing
• Intermediate Detailing
• Ordinary Detailing
– Many other checks/requirements
Why Seismic Design Categories?

99. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Response Modification Coefficient
• It reduces the design loads to account for the damping and ductility of the
structural system. An abbreviated set for values for R is found in Table
below.
99

100. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 100
• Typical Values
3.0 Ductile steel frames (Special Case)
2.5 Ductile concrete frames
2.5 Ordinary concrete frames
2.5 RC shear walls
2.5 Reinforced masonry shear walls
2.5 Unreinforced masonry shear walls
2.0 Ordinary steel frames
Over Strength Factor (Ω0)

101. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Flow Chart
101

102. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
• Ss and S1, mapped MCE
spectral accelerations are
0% to 300% and 0% to
100% in the map.
• For example, if the map
value is 125%g, it should
be input as 1.25g
Using ETABS For EQ Static Analysis (IBC 2006)
102

103. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
• UBC-97
Summary: UBC-97 versus IBC2006
• IBC-2000
RT
ICv
s
s
C
WCV

 CsWV 
R
IS
I
R
S
C EDS
E
DS
S 







RT
IS
T
I
R
S
C DI
E
DI
S 







Cv = 0.05 to 0.5
I = 1.0 to 1.5
R =
SDS = 0.13 to nearly 1.0
IE = 1 to 1.5
R = 4 to 8
SD1 = 0.05 to nearly 0.5
103

104. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Analysis Using
Response Spectrum
104

105. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
What are Response Spectra?
• For a ground acceleration at particular time, for a given time period and damping
ratio, a single value of displacement, velocity and acceleration can be obtained
• The output of the above (u, v, a) equation are the dynamic response to the ground
motion for a structure considered as a single DOF
• A plot of the “maximum” response for different ground motion history, different
time period and damping ratio give the “Spectrum of Response”
guuuu   2
2 
105

106. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Response Spectrum –
A picture is worth a concept
106
Graphical description of a response spectrum

107. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
What is Response Spectrum?
107

108. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
The Overall Picture …
108
Combined DVA response for El Centro ground motion, β = 2%

109. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Response Spectrum Generation
109

110. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Spectral Parameters
• Spectral Displacement Sd
• Pseudo Spectral Velocity Sv
• Pseudo Spectral Acceleration Sa
2
2
dt
ud
uva
dt
du
uv
u




dva
dv
SSS
SS
2




110

111. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Spectra for Different Soils
111

112. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
How to Use Response Spectra
• For each mode of free vibration, the corresponding Time Period is obtained.
• For each Time Period and specified damping ratio, the specified Response
Spectrum is read to obtain the corresponding Acceleration
• For each Spectral Acceleration, the corresponding velocity and displacements
response for the particular degree of freedom is obtained
• The displacement response is then used to obtain the corresponding stress
resultants
• The stress resultants for each mode are then added using some combination rule to
obtain the final response envelope
112

113. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
• ABS SUM Rule
Add the absolute maximum value
from each mode. Not so popular
and not used so much used
• SRSS
Square Root of Sum of Squares of
the peak response from each
mode. Suitable for well separated
natural frequencies
• CQC
Complete Quadric Combination is
applicable to large range of
structural response and gives
better results than SRSS.


N
n
no rr
1
0
Modal Combination Rules


N
n
no rr
1
2
0
 

N
i
N
n
niino rrr
1 1
00
113

114. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Response Spectrum Analysis


n
i
imi
m g
w
M
1
2

1. Develop the Mathematical Model of the Structure
2. Determine Mode Shapes by Eigen Value Analysis
3. For Each Mode m, determine:


n
i
imi
m g
w
L
1

Eq Participation Factor
Modal Mass
114

115. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
Response Spectrum Analysis


n
i
iwW
1
g
M
L
W
m
m
m
2

WM
gL
PM
m
m
2

Effective Weight
Participating Mass
Where;
115

116. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar
4. Determine the Number of Modes to be Considered to represent at least
90% of the participating mass of Structure
5. Determine the Spectral Acceleration and Seismic Design Coefficients for
each mode:
a. For Design response spectrum (UBC) determine Sam for Tm
b. Determine modal Seismic design coefficient
I = Importance Factor; R = Response Modification Factor
Response Spectrum Analysis
R
I
SC amm �