Mrs. Sangeeta Wiz is a renowned Civil Engineer from Delhi College of Engineering with MTech from IIT Delhi. She has spent 34 years in the building design industry. She is Managing Partner of SD Engineering Consultants, a 20-year-old Engineering Consultancy firm in India and also a Member of BNI Delhi - South. In past She has worked as DGM in RITES and Director (Technical) at AECOM before starting her Engineering Consultancy firm SDEC in 1996. She shared key points to consider while doing management of construction building projects. She emphasized on Symmetrical Design which remain safe during earthquake. She shared insights of structural design regarding safety and

1. PRATHAM
“Best Practices for Earthquake
Resistant Design”
SANGEETA WIJ
MEET NUMBER FOUR
On 5TH June 2018 at c/o The Entrepreneurship
School, O-113, Arjun Market, Block E, DLF Phase 1,
Sector 26A, Gururgram, Haryana 122002

2. Best Practices for an Earthquake
Resistant Design--a few
important tips
 Presented at by Sangeeta Wij at IHC on 2-12
Managing Partner
SD Engineering Consultants LLP
2

3. A GLARING SOFT STOREY ??
3

4. RESIDENTIAL LUXURY CONDOMINIUMS
IN NCR-FLAT PLATES AND COLUMNS??
4

5. COMMERCIAL TOWER –HOW
WE LOVE ASYMMETRY??
5

6. What are the Best Practices in structural
alysis/design ?
 Analysis, design diligently ,based on BIS 1893,875
and 456 using STAADPRO/ETABS/SAP2000
 Use Loads and Load Combinations as per BIS875-Part
V
 Provide Wall stiffness in the model,using diagonal
struts and use Time Period formula with Filler walls
if the Buildings has Masonry walls
 Use Formula for Bare Frame only if the structure
doesn’t have any masonry walls 6
Best Practices in Structural Analysis and design--a few common mistakes

7. Continued…
 Tall structures, if founded on soft soils, (N<10), must have
Pile or Raft Foundation.
 Liquefaction Potential must be verified in case the structures
are being founded on sandy soils, likely to have high water
tables.
 Storey Drift and deflections must be limited to acceptable
limits.
 Effect of thermal stresses must be incorporated by suitably
modifying Load Combinations wherever building block size
exceeds the recommended size of 40-45m
 (DL+LL+WL/EL+Temp Load)
 Wind Tunnel Test should preferably be carried outout for tall
structures(height> 150m)
7

8. Key points to ponder
8

9. What is a Collapse Prevention
design ?? Why do we need to
know?
World over the Earthquake Safety
of buildings is of four categories:
 Fully Operational
 Immediate occupancy
 Life Safety
 Collapse Prevention
9

10. SEISMIC GRADATION OF BUILDINGS
Earthquake Resistant buildings are of 4 types, Most buildings in
India follow the minimum code standards and therefore will be
classified as Category-D buildings for Earthquake Safety.

11. SEISMIC GRADATION OF BUILDING
Category-A: Fully Operational:
The building, its contents and utilities are
shaken by an earthquake, but no damage occurs
in either of the above; the function of the
building is not disrupted due to the occurrence
of the earthquake.
We must use Dampers and Base Isolation
devices to reach this level.
Non-Linear Performance Based design is
required instead of usual Static/ Dynamic
Analysis being carried out presently.
Use of SAP or equivalent softwares in place of
ETABS/STAADPRO currently under use.
Higher competence level of structural engineers
a must to be able to work with ASCE41 and
execute the designs/drawings accordingly.

12. 12
Category-B: Immediate Occupancy: The building, its contents and
utilities are shaken predominantly in their linear range of behavior
and only minor damage may occur in them; the use of prevailing
functions of the building and facilities is not restricted after the
earthquake so that its functioning can be resumed immediately after
the earthquake.

13. SEISMIC GRADATION OF BUILDING
Category-C: Life Safety: The building, its contents and
utilities are shaken severely in their non linear range of
behavior. Significant damage occurs in them, but the
building remains within its reserve capacity and does not
reach the state of imminent collapse. The use of the facility
is restricted after the earthquake until detailed structural
safety assessment is performed to ascertain the suitability of
the building for retrofitting. If found suitable for retrofitting,
the building maybe retrofitted.

14. 14
Category-D: Collapse Prevention: The building, its contents
and utilities are shaken severely in their non linear range of
behavior. Major damage occurs in them. The building does not
have any additional reserve capacity and is in the state of
imminent collapse. The building cannot be used after the
earthquake.

15. SEISMIC UPGRADATION OF
BUILDING
SEISMIC UPGRADATION COST DIFFERENCE
1. From Collapse Prevention to Life Safety 250/-
2. From Collapse Prevention to Immediate Occupancy 350/-
3. From Collapse Prevention to Fully Operational 700/-
4. From Life Safety to Immediate Occupancy 250/-

16. Why are BIS Codes still based on Collapse
Prevention??
 Least Cost and Ease of Analysis and design must
have prompted our Code makers to follow Collapse
Prevention post Independence.
 Performance Based designs coupled with Energy
dissipating devices are a must to upgrade Building
safety to higher levels.
 We must look beyond the Least Cost and give the
customer the choice to get the system designed to
his budget and his choice of Earthquake safety.
16

17. SOME DO’S & DON’TS FOR STRUCTURAL
ENGINEERS/ARCHITECTS/CLIENTS
 SAY NO TO HIDDEN BEAMS
 SAY NO TO FLOATING COLUMNS
 SAY NO TO FLAT SLABS IN HIGH SEISMIC
ZONES
 DONOT ADOPT irregular GEOMETRIES
 DONOT ADOPT ISOLATED FOOTINGS OR
PILE CAPS for soils with N<10
 Symmetrically place Shear Walls
preferably at building periphery and
design them to carry at least 75% Eq
Loads
17

18. Continued…
 Good old Expansion joints still work the best,
separating towers from low-rise and squatter
Podiums
 JOINTLESS LARGE DEVELOPMENTS TEND TO CRACK
UP ,ESPECIALLY AT TOP BASEMENT ROOF LEVEL
 SOFT STOREYS ARE LIKE BUTTER AND JELLY,WHEN
EARTHQUAKE STRIKES
 BASEMENT PARKINGS PREFERABLE OVER OPEN STILT
PARKINGS FOR STRUCTURAL HEALTH
 SAY YES TO A REGULAR GEOMETRY…LET’S LOOK AT
WHAT BIS 1893 PRESCRIBES
18

19. 19
PLAN IRREGULARITIES
Indian Code Specifies Five Types of Plan Irregularities
1. Torsion Irregularities (Should be avoided in zone III, IV and V)
Torsion Irregularities can
avoided
1. Plan aspect ratio < 3
2. Distribution of vertical
element resisting lateral
load should be balanced
according to mass in plan
∆2<1.5 ∆1

20. PLAN IRREGULARITIES
2. Re-entrant Corners
Plan has a projection in
direction of size< 15% of it
overall plan dimension in
that direction

21. PLAN IRREGULARITIES
3. Diaphragm Discontinuity
Floor slab
cutout/openings <50%
of total floor area

22. PLAN IRREGULARITIES
4. Out of Plan offset
In zone III,IV and
five should be
avoided

23. PLAN IRREGULARITIES
5. Non-Parallel Lateral Load Resisting System

24. VERTICAL IRREGULARITIES
1. Stiffness Irregularities
a. Soft Storey
Lateral Stiffness of the storey is less than 70% of the lateral stiffness of storey
above or less that 80% of the average lateral stiffness of three stories above
b. Extreme Soft Storey
Lateral Stiffness of the story is less than 60% of the lateral stiffness of story above
or less that 70% of the average lateral stiffness of three stories above
Building on Stilts are Fall Under These Categories

25. VERTICAL IRREGULARITIES

26. Effect of weak Storey

27. VERTICAL IRREGULARITIES
2. Mass Irregularities
The Seismic Weight of any Story is more than the 150 Percent of
that of the adjacent Storey

28. VERTICAL IRREGULARITIES
3. Vertical Geometric Irregularity
The Horizontal Dimension of lateral force resisting in any story is
more than 125% of that in adjacent story
Vertical geometric
irregularity when
L2>1.25 L1

29. 4. In-Plane Discontinuity in Vertical
Element Resisting Lateral Force
In-Plane Offset of the Lateral
Force Resisting Element Greater
Than the Length of Those Elements
(b>a)

30. VERTICAL IRREGULARITIES
5. Discontinuity in Capacity–Weak Storey
Earlier code : Story Lateral Strength is
Less Than 80% of That in The Story Above, are
the Weak Storey. When Lateral Strength of
F1<0.8 F2 then F1 is the weak Storey
Revised code : Story Lateral Strength is Less
Than of That in The Story Above, are the Weak
Storey. When Lateral Strength of F1< F2 then
F1 is the weak Storey

31. BUILDING CONFIGURATIONS
 SHOULD HAVE SIMPLE RECTANGULAR PLAN AND BE SYMMETRICAL BOTH WITH RESPECT TO MASS AND
RIGIDITY SO THAT THE CENTRES OF THE MASS AND RIGIDITY OF THE BUILDING COINCIDE WITH EACH OTHER
 BUILDINGS HAVING PLANS WITH SHAPES LIKE L, T, Y, E SHOULD BE SEPARATED INTO RECTANGULAR PARTS BY
PROVIDING SEPARATION GAPS AT APPROPRIATE LOCATIONS.

32. WHY SHOULD WE GO
REGULAR?
 A Closed Geometry works best in case of Horizontal
Loads like Earthquakes
 A Square or a Circular Configuration with nominal
Offsets or Setbacks in Plan or in Elevation
 An Open Flower Shaped Configuration is the worst
against Horizontal Loads and may Induce large
torsion/twisting
 Open Storeys were completely crushed in
Ahmedabad(ALSO ZONE-III,like HYDERABAD)
during 2002 Earthquake
 All soft storey columns and beams need to be designed
with 2.5 times earthquake Loads 32

33. DESIGN OF VERTICAL AND HORIZONTAL
PROJECTIONS FOR 5 TIMES EARTHQUAKE
 The design as per clause 7.12.2.1&2 needs to
be revised for all cantilever beams/slabs and
columns supporting mumty, machine room
and water tanks on terrace, considering 5
times the earthquake loads applicable for
design of connections with the main building.
 Isolated footings in Zones 4&5 must be tied
using footing beams to avoid uneven
settlement and cracking at later on. Refer
clause 7.12.1 of IS 1893 (absence of ties may
be responsible for development of cracks as
visible in certain non-tower columns)
33

34. Salient features in Tall Buildings
Draft Code 10639
 This code is applicable for reinforced concrete (RC)
buildings of heights greater than 45 m, but less than
250 m, normally intended for use as residential,
office and other commercial buildings.
 This code may be used for design of medium- and
low-rise buildings (of heights equal to or less than
45m) also; the good practices mentioned in this
standard will add value to the design of the said
buildings.
 Expansion Joints are prohibited in basements of tall
buildings. 34

35.  Height Limit for Structural Systems
 The maximum building height (in m) shall not exceed values given in Table 1
for buildings with different structural systems.
35

36.  Slenderness Ratio
The maximum values of the ratio of height h to minimum Base Width shall not exceed
values given in Table 2. B
36

37.  The minimum dimension of a column :
(a) 15 times the largest beam bar diameter of the
longitudinal reinforcement in the beam passing through or
anchoring into the column joint,(for 25 dia beam r/f: 375mm
and for 32 dia beam bars: 480mm)
(b) or 300 mm.
 Special moment frame and shear walls shall not be
discontinued in lower storeys and supported on less stiff
and brittle elements.
Structural Wall Systems
 The thickness of structural wall shall not be less than
160mm or Hw/20, whichever is larger. E.g.For 45m tall
buildings, min wall thickness:225mm and so on
37

38. Frame Tube – Structural and Tube-In-Tube Wall System
The minimum requirements for reinforcement bar diameters in beams of moment
frames and tubes are given in Table 9.
38

39. FOUNDATIONS
 Geotechnical Investigations
 For geotechnical investigation, boreholes shall:
 (a) Be spaced at ~30m within the plan area of the building,
 (b) Be a minimum of 2 boreholes per tower, and
 (c) Have a depth of at least 1.5 times estimated width of
foundation.
 Depth of Foundation
 The embedded depth of the building shall be at least 1/15
of height of building for raft foundation and 1/20 of the
height of building for pile and piled raft foundation
(excluding pile length). But, when the foundation rests on
hard rock, this requirement may be relaxed.
39

40.  RECOMMENDATIONS FOR SEISMIC MONITORING
 Earthquake Shaking: All tall buildings in zone V & tall
buildings exceeding 150 m in Seismic Zone IV & III shall be
instrumented with tri-axial accelerometers to capture
translational and twisting behavior of buildings during
strong earthquake shaking.
 Wind Oscillations: Buildings over 150 height may be
instrumented with anemometers and accelerometers to
measure wind speed, acceleration and direction on top of
the buildings.
Foundation Settlement and Pressure Measurement
 Raft or Piled-raft shall be instrumented for monitoring
long-term pressure imposed by soil on the raft, at
appropriate number (at least 5) pressure pads below the
raft. Alternatively, piles can be instrumented with strain
gauges at their top to measure the load on them.
40

41. Salient Changes in NDMA
Guidelines for Hospitals
 the Critical units need to be designed to Immediate Occupancy level and the rest
to Life Safety, both requiring Performance Based /Non Linear Analysis
Structural analysis/design has to be based on ASCE41 assisted by Base
Isolators/Dampers.
 Current Static/Dynamic analyses carried out on STAADPRO/ETABS will not be
adequate and more sophisticated softwares will need to be used.
 Buildings need to follow Regular geometry as per IS1893 definitions
 No Soft/Weak storeys are permitted(referring to stilted floors/ service floors etc)
No hidden beams /Floating Columns
41

42. CONCLUSIONS
 CLIENTS MUST AWARD WORK TO STRUCTURAL DESIGN
ENGINEERS DIRECTLY
 ALL PROCUREMENT PROCESSES INCLUDING
CONTRACTERS, ENGINEERS,REVIEWERS TO ENSURE
QUALITY
 ALL STRUCTURAL DESIGN/ REVIEW PROCESS MUST
FOCUS ON HIGHER PERFORMANCE AND LONG TERM
SAFETY AND NOT ON STEEL REDUCTION.
 PAYMENTS TO STRUCTURAL CONSULTANTS MUST BE AT
PAR WITH GLOBAL STANDARDS AND NOT JUST “x” RS
PER SQ FEET
 PROFESSIONAL LIABILITY INSURANCE MUST BE IN PLACE
42

43. THANKS
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