CE 72.32 (January 2016 Semester) Lecture 3 - Design Criteria

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

2. Dr. Naveed Anwar
Executive Director, AIT Consulting
Affiliated Faculty, Structural Engineering
Director, ACECOMS
Design Criteria
Design of Tall Buildings

3. Dr. Naveed Anwar
• Introduction
– Introduction of Building
– Building Description
• Gravity Load and Lateral Load
Resisting Systems
• Representative Drawings
– Codes, Standards and References
• Loading Criteria
– Dead Load
– Superimposed Dead Load
– Live Load
– Wind Load
– Seismic Load
– Load Combinations
• Ultimate Strength Design
• Allowable Stress Design
Overview of a Typical
Design Criteria Document
• Materials
– Concrete
– Reinforcing Steel
– Prestressed Strands, etc.
• Modeling, Analysis and Design
Procedures
– Analysis Procedures
– Design Procedures
– Analysis and Design Software
– Modeling Procedures and
Assumptions
• Beams and Columns
• Slabs and Band Beams
• Shear Walls
• Foundation
• Acceptance Criteria
– Story Drift
– Lateral Displacement
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4. Dr. Naveed Anwar
Introduction
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• Building Description and Location
– General
– Seismic and Wind Force Resisting System
– Drawings
– Codes and References

5. Dr. Naveed Anwar
Loading Criteria
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6. Dr. Naveed Anwar
Loads to Actions
• Loads
• Load Cases
• Load Combinations
• Design Envelopes
• Design Actions
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7. Dr. Naveed Anwar
Load Cases
• Load cases are defined by the user and are used for analysis purposes only.
• Static Load Cases
– Dead Load
– Live Load
– Wind Load
• Earthquake Load Cases
– Response Spectrum Load Cases
– Time History Load Cases
• Static Non-Linear Load Cases
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8. Dr. Naveed Anwar
Loading Criteria
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• Dead Load Material Unit Weight
(kN/m3)
Aluminum 27.0
Asphalt 21.2
Brass 83.6
Bronze 87.7
Brick 18.9
Cement 14.7
Coal, loose 8.8
Concrete
Stone aggregate
(unreinforced)
Brick aggregate
(unreinforced)
22.8
20.4

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• Live Load
Loading Criteria
Occupancy Use of Floor
Load per Unit
Area (kN/m2)
One or two-family
dwellings
 Uninhabitable attics without storage
 Uninhabitable attics with storage
 Habitable attics and sleeping areas
 All other area except stairs and balconies
0.48
0.96
1.44
1.92
Hotels and multifamily
houses
 Private rooms and corridors serving them
 Public rooms and corridors serving them
1.92
4.79

10. Dr. Naveed Anwar 10
• Seismic Load
Loading Criteria
Parameter Value
Seismic Zone 4
Seismic Source Type A
Importance Factor (Ie) 1.0
Distance to Near Source 1.5 Km
Soil Profile Type Sc
Lateral System
Bearing Wall System/Special Reinforced
Concrete Shear Wall
Coefficient for the inherent overstrength and
global ductility capacity of lateral force resisting
system (R)
4.5 (UBC97, Table 16-N)
Seismic Force Amplification Factor (Ω0) 2.8 (UBC97, Table 16-N)

11. Dr. Naveed Anwar 11
• Wind Load
Loading Criteria
Parameter Value
Basic Wind Speed, 3 second gust (V) 96 mph (155 kph)
Exposure B
Occupancy Category II
Importance Factor (Iw) 1.0
Enclosure Classification Enclosed
Mean Roof Height (h) 257 meters

12. Dr. Naveed Anwar
Loading Criteria
12
Strength Design Method:
• 1.4D
• 1.2D + 1.6L + 0.5Lr
• 1.2D + 1.0L + 1.6W + 0.5Lr
• 1.2D + 1.0L + 1.4E
• 0.9D + 1.6W
• 0.9D + 1.4E
Serviceability Check:
• 1.0D
• 1.0D + 1.0L
• 1.0D + 0.75L + 0.75W + 0.75Lr
• 1.0D + 0.75L + 0.75E + 0.75Lr
• 1.0D + 1.0W
• 1.0D + 1.0E
• 0.6D + 1.0W
• 0.6D + 1.0E

13. Dr. Naveed Anwar
Load Combinations
• The Load Combinations may be created by the program, user defined or a
combination of both.
• Some Examples: [Created by the program]
– 1.4ΣDL
– 1.4ΣDL + 1.7(ΣLL + ΣRLL)
– 0.75[1.4ΣDL + 1.7(ΣLL + ΣRLL) + 1.7WL]
– 0.75[1.4ΣDL + 1.7(ΣLL + ΣRLL) - 1.7WL]
– 0.9ΣDL + 1.3WL
– 0.9ΣDL - 1.3WL
– 1.1 [1.2ΣDL + 0.5(ΣLL + ΣRLL) + 1.0E]
– 1.1 [1.2ΣDL + 0.5(ΣLL + ΣRLL) - 1.0E]
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14. Dr. Naveed Anwar
Total
Obtaining Envelop Results
Max, P
Min, P
Comb1 Comb2 Comb3 CombN
Load Case -1
Load Case - 2
Load Case - 3
Load Case - M
Envelop Results
P1 P2 P3 PN
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15. Dr. Naveed Anwar
Can Envelop Results be Used for Design?
• Actions interact with each other, affecting the
stresses
• For Column Design: P, Mx, My
• For Beam Design: Mx, Vy, Tz
• For Slabs: Mx, My, Mxy
• At least 3 actions from each combination must
be considered together as set
• Therefore, Envelop Results cannot be used
• Every load combinations must be used for design
with complete “action set”
P
Mx
My
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16. Dr. Naveed Anwar
Design Actions For Static Loads
• For static loads, Design
Actions are obtained as the
cumulative result from each
load combination as set for
all interacting actions
• The final or critical results
from design of all load
combinations are adopted
Combinations
LoadCases
Design
Actions
Obtained as
set from all
Combinations
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17. Dr. Naveed Anwar
Static, Dynamic and Nonlinear Results
• For a Single Action:
– Static Load Case
– Response Spectrum Load Case
– Time History Load Case
– Static Non-linear Load Case
1
+
-
1 for each Time Step
OR 1 for envelop
1 for each Load Step
Load
Combination
Table
OR 1 for Envelop
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18. Dr. Naveed Anwar
Response Spectrum Results for Action Set
• Design Actions needed for Columns
+P, +Mx, +My
+P, +Mx, -My
+P, -Mx, +My
+P, -Mx, -My
-P, +Mx, +My
-P, +Mx, -My
-P, -Mx, +My
-P, -Mx, -My
Maximum Results obtained by:
SRSS, CQC, etc.
P, Mx, My>
LoadCombinationTable
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19. Dr. Naveed Anwar
Time History Analysis Results
• Response Curve for One Action
Min Val
Max Val
Option – 1:
Envelope Design
T (sec)
Option – 2:
Design For All Values
(At each time step)
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20. Dr. Naveed Anwar
Wind Load Cases
• At least 3 basic Wind Load Cases should be considered
– Along X-Direction
– Along Y-Direction
– Along Diagonal
• Each Basic Wind Load Case should be entered separately
into load combinations twice, once with (+ve) and once
with (-ve) sign
• A total of 6 Wind Load Cases should be considered in
Combinations, but only 3 Load Cases need to be defined
and analyzed
Wx
Wy
Wxy
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21. Dr. Naveed Anwar
Wind Load Combinations
(f)- Load factor specified for Wind in
the design codes
Six Additional Load Combinations are
required wherever “Wind” is
mentioned in the basic Load
Combinations
Example:
Comb = 0.75(1.4D + 1.7W) will
need Six Actual Combinations
Comb1= 0.75 (1.4D + 1.7Wx)
Comb2 = 0.75 (1.4D - 1.7Wx)
Comb3 = 0.75 (1.4D + 1.7Wy)
Comb4 = 0.75 (1.4D - 1.7Wy)
Comb5 = 0.75 (1.4D + 1.7Wxy)
Comb6 = 0.75 (1.4D - 1.7Wxy)
Comb1 Comb2 Comb3 Comb4 Comb5 Comb6
Wx +f -f 0 0 0 0
Wy 0 0 +f -f 0 0
Wxy 0 0 0 0 +f -f
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22. Dr. Naveed Anwar
Seismic Load Criteria Example
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Parameter Value
Spectral acceleration (5% damped) at short periods (0.2 s) of horizontal
ground motion (2500-yr. return period), SS
0.77 g
Spectral acceleration (5% damped) at long periods (1 s) of horizontal ground
motion (2500-yr. return period), S1
0.31 g
Spectral acceleration (5% damped) at short periods (0.2 s) of horizontal
ground motion (2500-yr. return period) adjusted for site class effects, SMS
0.92 g
Spectral acceleration (5% damped) at long periods (1 s) of horizontal ground
motion (2500-yr. return period) adjusted for site class effects, SM1
0.55 g
Design spectral acceleration (5% damped) at short periods (0.2 s) of
horizontal ground motion (500-yr. return period), SDS
0.61 g
Design spectral acceleration (5% damped) at short periods (1 s) of horizontal
ground motion (500-yr. return period), SD1
0.37 g
Site class D
Short period site coefficient, Fa 1.192
Long period site coefficient, Fv 1.78
Response modification coefficient, R 5

23. Dr. Naveed Anwar
Materials
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24. Dr. Naveed Anwar
Materials
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Concrete Reinforcing Steel
Member fc' (psi)
Mat slab 3,500
Columns and
shear walls
4,500
Girders and
slabs
3,500
Bar Diameter (in) fy (psi)
ϕ3/8” and smaller
bars
40,000
ϕ1/2" and larger
bars
60,000

25. Dr. Naveed Anwar
Materials
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Properties Value
Minimum yield stress, Fy 1,689 MPa
Minimum tensile stress, Fu 1,860 MPa
7-wire prestressed strand diameter 12.7 mm
Prestressed Strands

26. Dr. Naveed Anwar
Modeling, Analysis and Design
Procedures
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27. Dr. Naveed Anwar
Design Procedures
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Preliminary Design Phase
Develop the structural system and review the primary
responses such as mode shapes, natural periods, base
shear, story drifts, and lateral displacements. Determine
the size of primary structural components.
Detailed Design
Perform the detailed analysis and design of all structural
members and connections, considering the stability of
structure as a whole, and each of its elements. Prepare
detailed drawings and specifications, supported by
extensive calculations and analyses.
Preliminary Design
Phase
Detailed Design

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• Procedures
– Modal Analysis
• Combination of mass from 100% of dead load and superimposed dead
load plus 25% of live load
• Sufficient number of modes
– Linear static analysis
– Response spectrum analysis
• Complete Quadratic Combination (CQC)
• 100 % of the prescribed horizontal seismic forces in one direction plus 30 %
of the prescribed horizontal seismic design forces in the perpendicular
direction.
• Damping
Modeling, Analyzing, Acceptance Criteria

29. Dr. Naveed Anwar
Modeling, Analyzing, Acceptance Criteria
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• Analysis and Design Software
– ETABS 9.7.2
• Modeling Procedures and Assumptions
– Component Stiffness and Strength
• Cracked sections for seismic analysis
• Gross section for wind analysis
• Nominal strength of materials shall be used in the determination of
modulus of elasticity.

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• Soil-Structure Interaction
– Springs representing the effects of soil on the foundation system
– The vertical and horizontal spring stiffness shall be determined based on the
lateral and vertical sub-grade reaction modulus of the soil.
• Beams and Girders
– Frame elements
– Insertion points and end offsets
– End releases
Modeling, Analyzing, Acceptance Criteria

31. Dr. Naveed Anwar 31
• Columns
– Frame elements
– Insertion points and end offsets
– End releases
• Slabs
– Shell elements
– Rigid diaphragm assumption shall not be applied
Modeling, Analyzing, Acceptance Criteria

32. Dr. Naveed Anwar 32
• Shear Walls
– Shell elements
– Meshed wall elements
– Orientation
• Coupling Beams
– Either frame elements or shell elements
– Beam elements must be connected to the shear walls by imbedded beam
elements, which will extend across the width of the shear wall.
Modeling, Analyzing, Acceptance Criteria

33. Dr. Naveed Anwar 33
• Damping
– to represent the dynamic effects in the design of the building
• Acceptance Criteria
– All demand/capacity ratios for the strength design shall be less than 1.
– The inelastic story drift under seismic loading is limited to 2% (for
fundamental period greater than 0.7 sec).
– The elastic story drift under wind loading is limited to (2% /R / factor used in
calculation of inelastic drift under seismic load).
– Maximum lateral displacement of the building is limited to H/200 (H=height
of the building).
Modeling, Analyzing, Acceptance Criteria

34. Dr. Naveed Anwar
Executive Director, AIT Consulting
Affiliated Faculty, Structural Engineering
Director, ACECOMS
Thank You