EARTHQUAKE RESISTANT DESIGN OF
REINFORCED CONCRETE BUILDING BASED ON
IS : 1893 (PART1)-2016
October, 2019
By Anil Kumar Sariar, Shamvwi Consultant
414, Jagat Trade Center, Fraser Road,Patna
Email Id : shamvwi@gmail.com
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
1
Earthquake
An earthquake is a sudden, rapid shaking of the Earth
caused by the release of strain energy stored in rocks.
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 2
The Elegant (but Unsafe) Central Library Building
A. K. Sariar, Shamvwi Const.
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3
A. K. Sariar, Shamvwi Const.
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A. K. Sariar, Shamvwi Const.
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A. K. Sariar, Shamvwi Const.
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A. K. Sariar, Shamvwi Const.
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7
Earthquake Design is special

Earthquake Effects versus Wind Effects
Droof
Fw
Movement under Building
A. K. Sariar, Shamvwi Const.
Pressure on Building
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Lecture 1 / slide 8
Earthquake Design is special

Movement under the building

Inertia forces at masses
..
- mug (t)
Mass m
..
ug (t)
Moving-base Structure
A. K. Sariar, Shamvwi Const.
Fixed-base Structure
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Lecture 1 / slide 9
Earthquake Design is special
Movement under the building
F
Earthquake Behaviour
:: Inelastic
Droof
Lateral Load F

Wind Behaviour
:: Elastic
0
A. K. Sariar, Shamvwi Const.
Lateral Deformation D
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Lecture 1 / slide 10
Built Environment

Inverted Pendulum
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 11
Built Environment

Traditional design

Under same earthquake shaking

Max. response of structures different with T
Earthquake Shaking
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 12
Built Environment

Traditional design

Design Earthquake Force

Soil effect
Flexible Wall
Soil
Original Building
A. K. Sariar, Shamvwi Const.
Flexible Soil
Inverted Pendulum Model
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Lecture 1 / slide 13
Built Environment

Behaviour


Mass
Stiffness
Light
Heavy
Twist
Swing
with equal ropes
A. K. Sariar, Shamvwi Const.
Building
with heavy mass on one side
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Lecture 1 / slide 14
Built Environment

Behaviour


Mass
Stiffness
Swing
with unequal ropes
A. K. Sariar, Shamvwi Const.
Building
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on slope
Lecture 1 / slide 15
Buildings with Parking
230mm
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 16
Bullish India
Sequence of Design
Sequence of Construction
Logical Sequence of Design & Construction
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 17
Bullish India
Sequence of Design
as practiced in many buildings in India
Sequence of Construction
Indian Practice of Design & Construction
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 18
Earthquake Resistance

Structural Elements
Structural Wall
(Vertical Element)
Floor Slab
(Horizontal
Diaphragm)
Load Path
Soil
A. K. Sariar, Shamvwi Const.
Foundation
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Lecture 1 / slide 19
A. K. Sariar, Shamvwi Const.
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20
Earthquake Design is special

Earthquake Effects

Damage expected in normal structures

Earthquake-RESISTANT not Earthquake-PROOF
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 21
SECTION 1
This Section covers
Foreword, Scope and References
IS:1893-2016(Part I)
A. K. Sariar, Shamvwi
Const.
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Oct. 2019
22
Different Parts of IS:1893





Part 1: General Provisions and Buildings
Part 2: Liquid Retaining Tanks – Elevated and
Ground Supported
Part 3: Bridges and Retaining Walls
Part 4: Industrial Structures Including Stack Like
Structures
Part 5: Dams and Embankments
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 23
What does IS:1893 Cover?


Specifies Seismic Design Force
Other seismic requirements for design, detailing
and construction are covered in other codes


e.g., IS:4326, IS:13920, ...
For an earthquake-resistant structure, one has
to follow IS:1893 together with seismic design
and detailing codes.
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 24
Coverage of Part 1

General Provisions






Applicable to all structures like building, parking
structure and ancillary structures.
Liquid retaining structure
Bridges
Embankments and retaining wall
Industrial structures
Concrete Masonry and earth dam
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 25
Major Changes





Design Spectra are defined for natural period up
to 6s;
Same design response spectra are specified for
all buildings, irrespective of material of
construction.
Dynamic analysis has been recommended for
zone other than II.
Effect of brick wall is included and expressions
for the same has been provided.
Consideration for soft storey is provided logically
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 26
Zone Map


Zone II to Zone III have been defined.
The Annex E of the code gives zone and Z for cities
with population more than 3Lakh.
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 27
Other Effects

Earthquakes can cause damage in a number of
ways. For instance:

Vibration of the structure: this induces inertia
force on the structure






By inertia force, we mean mass times acceleration
Landslide triggered by earthquake
Liquefaction of the founding strata
Fire caused due to earthquake
Flood caused by earthquake
The code generally addresses only the
first & 3rd aspect
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 28
Seismic Hazard

The criterion for seismic zones remains same as
before
Zone
Area liable to shaking intensity
II
VI (and lower)
III
IV
V
VII
VIII
IX
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 29
Foundation and Soil Factor

Soil has been classified as hard soil site, medium
stiff soil sites and Soft soil site. Theses soil types
has been classified on basis of soil type and N
value and given in table 2 of the code.
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 30
Response Spectrum

During ground shaking, one can measure
ground acceleration versus time (accelerogram)
using an accelerograph


Accelerograph is the instrument
Accelerogram is the record obtained from it


Accelerogram is the variation of ground acceleration with
time (also called time history of ground motion)
Unless otherwise mentioned, response spectrum is based on
a linear elastic system
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 31
Typical Accelerograph
This is a typical analog instrument. These days, digital instruments are
becoming popular (photo from Earthquakes by Bolt)
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 32
Typical
Accelerograms
From Dynamics of Structures
by A K Chopra, Prentice Hall
Time, sec
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 33
Response Spectrum (contd…)

If the ground moves as per the given
accelerogram, what is the maximum response of
a single degree of freedom (SDOF) system (of
given natural period and damping)?
Response may mean any quantity of interest,
e.g., deformation, acceleration

T=2 sec,
Damping  =2%
a(t)/g
Ground motion time history
A. K. Sariar, Shamvwi Const.
Time, sec
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Lecture 1 / slide 34
Response Spectrum (contd…)

By response we may mean any response
quantity of interest to us, for example:

Absolute acceleration of the mass


Relative velocity of the mass with respect to
base


Termed as Velocity Response Spectrum
Relative displacement of the mass with respect
to base


Termed as Acceleration Response Spectrum
Termed as Displacement Response Spectrum
Word Spectra is used to denote plural of
Spectrum.
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 35
Response Spectrum (contd…)


Response spectrum is a very powerful tool.
Uses of response spectrum:



To obtain maximum response of a SDOF system
(to the original accelerogram using which
response spectrum was obtained)
To obtain maximum response in a particular
mode of vibration of a multi degree of freedom
(MDOF) system
It tells about the characteristics of the ground
motion (accelerogram)
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 36
Zone Factor (Z)

The code uses a single parameter: Zone Factor
(Z).
Zone
V
Z
0.36
IV
III
II
0.24
0.16
0.10
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 37
Modal Mass


It is that mass of the structure which is effective
in one particular natural mode of vibration
Can be obtained from the equation in Cl. 7.7.5.4
for simple lumped mass systems



It requires one to know the mode shapes
One must perform dynamic analysis to obtain
mode shapes
See example in next slides to appreciate the
physical significance of Modal Mass
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 38
Seismic Weight (Cl.3.26)

It is the total weight of the building plus that
part of the service load which may reasonably
be expected to be attached to the building at
the time of earthquake shaking.



It includes permanent and movable partitions,
permanent equipment, etc.
It includes a part of the live load
Buildings designed for storage purposes are
likely to have larger percent of service load
present at the time of shaking.

Notice the values in Table 10
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 39
Centre of Stiffness


Cl. 4.5 defines Centre of Stiffness for single
storey and multi Storey building separately
as The point through which the resultant of the

restoring forces of a system acts.
For single Storey building it is one point while
for multistory building, it is set of points on
horizontal floor

It is defined as:
If the building undergoes pure translation in the
horizontal direction (that is, no rotation or twist or
torsion about vertical axis), the point through
which the resultant of the restoring forces acts is
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 40
the Centre of
Stiffness

Centre of Rigidity

Both Centre of Stiffness (CS) and Centre of
Rigidity (CR) are the same terms for our
purposes.
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 41
Eccentricity

Cl. 4.6 defines Static Eccentricity.


This is the calculated distance between the
Centre of Mass and the Centre of Stiffness.
Under dynamic condition, the effect of
eccentricity is higher than that under static
eccentricity.


Hence, a dynamic amplification is to be applied
to the static eccentricity before it can be used in
design.
cl. 7.82 provides an amplification of 1.5 to the
computed eccentricity (cl. 4.6).
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 42
Eccentricity (contd…)

An accidental eccentricity is also considered
because:



The computation of eccentricity is only
approximate.
During the service life of the building, there could
be changes in its use which may change centre
of mass.
Design eccentricity (cl.4.6) is obtained from
static eccentricity by accounting for (cl.7.8.2)


Dynamic amplification, and
Accidental eccentricity
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 43
Dual System


Consider buildings with shear walls and moment
resisting frames.
In 1984 version of the code, Table 5 (p. 24)
implied that the frame should be designed to
take at least 25% of the total design seismic
loads.
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 44
Dual System (contd…)

In the new code several choices are available to
the designer:

When conditions of Cl. 4.9 are met: dual system.


Example 1: Analysis indicates that frames are taking 30% of
total seismic load while 70% loads go to shear walls. Frames
and walls will be designed for these forces and the system
will be termed as dual system.
Example 2: Analysis indicates that frames are taking 10%
and walls take 90% of the total seismic load. To qualify for
dual system, design the walls for 90% of total load, but
design the frames to resist 25% of total seismic load
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 45
Dual System (contd…)

Conditions of Cl. 4.9 are not met. Here, two
possibilities exist (see Footnote 4 in Table 7, p. 23):


Frames are not designed to resist seismic loads. The entire
load is assumed to be carried by the shear walls. In Example
2 above, the shear walls will be designed for 100% of total
seismic loads, and the frames will be treated as gravity
frames (i.e., it is assumed that frames carry no seismic
loads)
Frames and walls are designed for the forces obtained from
analysis, and the frames happen to carry less than 25% of
total load. In Example 2 above, the frames will be designed
for 10% while walls will be designed for 90% of total seismic
loads.
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 46
Dual System (contd…)


Clearly, the dual systems are better and are
designed for lower value of design force.
See Table 7 (p. 23) of the code. There is different
value of response reduction factor (R) for the
dual systems.
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 47
Moment Resisting Frame


Cl. 4.14 defines Ordinary and Special Moment
Resisting Frames.
Ductile structures perform much better during
earthquakes.



Hence, ductile structures are designed for lower
seismic forces than non-ductile structures.
For example, compare the R values in Table 9
IS:13920-2016 provides provisions on ductile
detailing of RC structures for seismic
performance.
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 48
Number of Storeys (Cl.4.15)

When basement walls are connected with the
floor deck or fitted between the building
columns, the basement storeys are not included
in number of storeys.

This is because in that event, the seismic loads
from upper parts of the building get transferred
to the basement walls and then to the
foundation. That is,



Columns in the basement storey will have insignificant
seismic loads, and
Basement walls act as part of the foundation.
In new code, Cl. 7.6 requires height of building.
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 49
Soft Story




Cl. 4.20 defines Soft Storey
It is defined as Storey having less lateral
stiffness than that of upper Storey. It is
calculated as storey shear divided Storey drift.
Storey drift: It is relative displacement between
floors of storey under consideration.
Most Indian buildings will be soft storey as per this definition
simply because the ground storey height is usually different
from that in the upper storeys.
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 50
Weak Storey (Cl 4.20.2)

Note that the stiffness and strength are two
different things.





Stiffness: Force needed to cause a unit
displacement. It is given by slope of the forcedisplacement relationship.
Strength: Maximum force that the system can
take
Soft storey refers to stiffness
Weak storey refers to strength
Usually, a soft storey may also be a weak
storey
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 51
Storey Drift


Storey Drift defined in cl. 4.21 of the Code.
Cl. 7.11.1 of the code provides:


Storey drift not to exceed 0.004 times the storey
height.
Table 6 of the code provides:

Storey drift not to exceed 0.002 times the storey
height in case of soft storey.
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 52
Earthquake Design Principle


Large earthquakes are infrequent as compared
to smaller earthquakes
The criteria is:




Minor (and frequent) earthquakes should not
cause damage
Moderate earthquakes should not cause
significant structural damage (but could have
some non-structural damage)
Major (and infrequent) earthquakes should not
cause collapse
Read Earthquake Tip 8
(http://www.nicee.org/EQTips/EQTip08.pdf)
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 53
Seismic Design Principle

A well designed structure can withstand a
horizontal force several times the design force
due to:



Overstrength
Redundancy
Ductility
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 54
Overstrength

The structure yields at load higher than the
design load due to:

Partial Safety Factors




Material Properties






Partial safety factor on seismic loads
Partial safety factor on gravity loads
Partial safety factor on materials
Member size or reinforcement larger than required
Strain hardening in materials
Confinement of concrete improves its strength
Higher material strength under cyclic loads
Strength contribution of non-structural elements
Special ductile detailing adds to strength also
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 55
Redundancy



Yielding at one location in the structure does not
imply yielding of the structure as a whole.
Load distribution in redundant structures
provides additional safety margin.
Sometimes, the additional margin due to
redundancy is considered within the
“overstrength” term.
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 56
Ductility

As the structure yields, two things happen:



There is more energy dissipation in the structure
due to hysteresis
The structure becomes softer and its natural
period increases: implies lower seismic force to
be resisted by the structure
Higher ductility implies that the structure can
withstand stronger shaking without collapse
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 57
Response Reduction Factor



Overstrength, redundancy, and ductility
together lead to the fact that an earthquake
resistant structure can be designed for much
lower force than is implied by a strong shaking.
The combined effect of overstrength,
redundancy and ductility is expressed in terms
of Response Reduction Factor (R)
See Fig. on next slide.
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 58
Δ
Total
Horizontal
Load
Total Horizontal Load
Maximum force
if structure remains elastic Fel
Linear Elastic
Response
Maximum
Load Capacity Fy
Load at
First Yield
Fs
Due to
Ductility
Non linear
Response
Due to
Redundancy
First
Significant
Yield
Due to
Overstrength
Design force Fdes
0
Δw
Δy
Figure: Courtesy
Dr. C V R Murty
Δmax
Roof Displacement (Δ)
Response Reduction Factor 
A. K. Sariar, Shamvwi Const.
Maximum Elastic Force (Fel)
Design Force (Fdes)
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Lecture 1 / slide 59
Cl. 6.1.3 & Cl 6.1.4.



Imply that the earthquake resistant structures
should generally be ductile.
IS:13920-2016 gives ductile detailing
requirements for RC structures.
IS:13920-2016 provides condition for stronger
column and weaker beam. Sum of Ultimate
flexural capacity of Columns and that of Beams
>=1.4.
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 60
Soil Structure Interaction (Cl. 6.1.5)



If there is no structure, motion of the ground surface is
termed as Free Field Ground Motion
Normal practice is to apply the free field motion to the structure
base assuming that the base is fixed.
 This is valid for structures located on rock sites.
 For soft soil sites, this may not always be a good
assumption.
Presence of structure modifies the free field motion
since the soil and the structure interact.


Hence, foundation of the structure experiences a motion
different from the free field ground motion.
The difference between the two motions is
accounted for by Soil Structure Interaction (SSI)
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 61
Direction of Ground Motion

During earthquake shaking, ground shakes in all
possible directions.


Direction of resultant shaking changes from
instant to instant.
Basic requirement is that the structure should
be able to withstand maximum ground motion
occurring in any direction.

We already discussed that for most structures,
main concern is for horizontal vibrations rather
than vertical vibrations.
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 62
Direction of Ground Motion (contd…)



One does not expect the peak ground
acceleration to occur at the same instant in two
perpendicular horizontal directions.
Hence for design, maximum seismic force is not
applied in the two horizontal directions
simultaneously.
If the walls or frames are oriented in two
orthogonal (perpendicular) directions:

It is sufficient to consider ground motion in the
two directions one at a time.
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 63
Liquefaction Cl.6.3.5.3


It points out that in case of loose or medium
dense saturated soils, liquefaction may take
place.
Sites vulnerable to liquefaction require



Liquefaction potential analysis.
Remedial measures to prevent liquefaction.
Else, deep piles are designed assuming that soil
layers liable to liquefy will not provide lateral
support to the pile during ground shaking.
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 64
Liquefaction Potential



Information given in cl.6.3.5.3 and Table 2 on
Liquefaction Potential is very primitive:
A simplified method is given in Annex F for
determining liquefaction potential analysis.
It is common these days to use SPT or CPT
results for detailed calculations on liquefaction
potential analysis.
A. K. Sariar, Shamvwi Const.
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Lecture 1 / slide 65
Vertical Acceleration Cl.6.4.6


It is estimated with S/g=2.5
Vertical acceleration has been taken two-third of
horizontal acceleration
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 66
Regular and Irregular Configuration (Cl. 7.1)


The statement of Cl. 7.1 is an attempt to
emphasize the importance of structural
configuration for ensuring good seismic
performance.
Good structural configuration has implications
for both safety and economy of the building.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 67
Regular versus Irregular Configuration

Tables 5 and 6 list out the irregularities in the
building configuration


Table 5 and Fig. 3 for Irregularities in Plan
Table 6 and Fig. 4 for Irregularities in Elevation
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 68
Building Plans with Orthogonal Systems
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 69
walls
Building Plans with Non-Orthogonal Systems
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 70
Torsional Irregularity

Uneven Distribution of mass
Heavy
Mass
Vertical Components of Seismic Resisting System
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 71
Torsional Irregularity (contd…)



Geometrically building may appear to be regular
and symmetrical, but may have irregularity due
to distribution of mass and stiffness.
It is better to distribute the lateral load resisting
elements near the perimeter of the building
rather than concentrate these near centre of the
building.
See fig. on next slide
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 72
(a)
(b)
Arrangement of shear walls and braced frames-not recommended.
Note that the heavy lines indicate shear walls and/or braced frames
Fig. From
NEHRP
Commentary
(a)
(b)
Arrangement of shear walls and braced frames- recommended.
Note that the heavy lines indicate shear walls and/or braced frames
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 73
Torsional Irregularity (contd…)

Table 5 says that torsional irregularity exists if the drift
(lateral displacement) at one end of the building is more
than 1.5 times the minimum of the drift at the two ends.
Δ1
Δ2
Torsional irregularity when Δ2> 1.5[(Δ1)]
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 74
Re-entrant Corner


When an otherwise regular building has a large
re-entrant corner, wings of the building tend to
vibrate in a manner different from that of the
entire building.
Hence, building treated as irregular when offset
dimension exceeds 15% of the total dimension.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 75
Re-entrant Corner (contd…)

Fig 3 of code shows the plan irregularity as hereunder

Note that upper parts of the figure show 15% to 20%. It will
save confusion if the figure showed only 15%. Code has
taken fig from NEHRP Commentary.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 76
Diaphragm Discontinuity



Diaphragm discontinuity changes the lateral load
distribution to different elements as compared
to what it would be with rigid floor diaphragm.
Also, it could induce torsional effects which may
not be there if the floor diaphragm is rigid.
Observe the top two figures of page 20.


Again, these are from NEHRP Commentary and not
traced correctly in our code.
See next slide.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 77
Diaphragm Discontinuity (contd…)
RIGID
FLEXIBLE
O
DIAPHRAGM
P
E
N
DIAPHRAGM
Vertical Components of Seismic Resisting System
Discontinuity in Diaphragm Stiffness
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 78
Out-of-Plane Offsets


This is a very serious irregularity wherein there
is an out-of-plane offset of the vertical element
that carries the lateral loads.
Such an offset imposes vertical and lateral load
effects on horizontal elements, which are
difficult to design for adequately.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 79
Out-of-Plane Offsets (contd…)
Shear
Wall
Out-of-Plane Offset in Shear Wall
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 80
Stiffness Irregularity




It leads to soft storey condition.
Analysis is done for both bare frame and infill
frame.
Drift is restricted to 0.2%.
Structural wall density is kept to minimum 2%
of plan area in both direction.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 81
Mass Irregularity




Mass irregularity will be induced by the presence
of a heavy mass on a floor, say a swimming
pool.
Note that the mass irregularity in IS1893 has
been defined when weight of a floor exceeds
150% the weight of the adjacent floor.
NEHRP defines it when the weight exceeds
150% of that of the adjacent floor.
Dynamic analysis is performed.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 82
Stiffness & Mass Irregularity
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 83
Vertical Geometric Irregularity


Buildings with vertical offsets will fall in this
category.
Also, a building may have no apparent offset,
but its lateral load carrying elements may have
irregularity.


For instance, shear wall length may suddenly
reduce.
When building is such that larger dimension is
above the smaller dimension, it acts as an
inverted pyramid and is undesirable.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 84
Vertical Geometric Irregularity
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 85
Vertical Geometric Irregularity
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 86
Problems with Irregularities

In buildings with vertical irregularity, load
distribution with building height is different from
that in Cl. 7.7.1.


Dynamic analysis is required.
In buildings with plan irregularity, load
distribution to different vertical elements is
complex.


Floor diaphragm plays an important role and
needs to be modelled carefully.
A good 3-D analysis is needed.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 87
Problems with Irregularities (contd…)

In irregular building, there may be concentration
of ductility demand in a few locations.


Special care needed in detailing.
Just dynamic analysis may not solve the
problem.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 88
Design Lateral Force (Cl. 7.6)


two methods: Equivalent Static Method and
response spectrum method.
There have been instances of designer
calculating seismic design force for each 2-D
frame separately based on tributary mass
shared by that frame.


This is erroneous since only a fraction of the
building mass is considered in the seismic load
calculations.
See fig next slide
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 89
Mass that causes
Earthquake Force
in X-Direction
EQx
Mass being considered for
calculation of inertia force
due to earthquake
EQx
Plan of building
A. K. Sariar, Shamvwi Const.
Calculation of design seismic
force on the basis of
tributary mass on 2-D frames
leads to significant underdesign.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 90
Design Lateral Force (Cl. 7.6) (contd…)

Now, Cl. 7.6.1 makes it clear that one has to
evaluate seismic design force for the entire
building first and then distribute it to different
frames/ walls.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 91
Fundamental Natural Period (Cl. 7.6)


Major changes in empirical equations for natural
period.
Now:

For frame buildings without brick infills



For all other buildings, including frame buildings
with brick infill panels:


T = 0.075 h0.75,for RC frame bldgs
T = 0.085 h0.75,for steel frame bldgs
T = 0.09h/(d)
For RC structural wall:

T = 0.075h^0.75/(Aw) > = 0.09h/(d)
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 92

Vertical Distribution of Seismic Load (Cl. 7.6.3)
Lateral load distribution with building height
depends on



In low and medium rise buildings,



Natural periods and mode shapes of the building
Shape of design spectrum
Fundamental period dominates the response,
and
Fundamental mode shape is close to a straight
line (with regular distribution of mass and
stiffness)
For tall buildings, contribution of higher modes
can be significant even though the first mode
may still contribute the maximum response.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 93
Vertical Distribution of Seismic Load (Cl. 7.6.3) (contd…)

Hence, NEHRP provides the following expression for
vertical distribution of seismic load
Qi  VB
Wi hik
n
k
W
h
 j j
j 1


Where k = 1 for T ≤ 0.5sec, and k = 2 for T ≥ 2.5 sec.
Value of k varies linearly for T in the range 0.5 sec
to 2.5 sec.
In IS:1893 over the years, k = 2 has been taken
regardless of natural period

This is conservative value and has been retained
in current edition of the code also.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 94
Horizontal Distribution... (Cl. 7.6.4)


Floor diaphragm plays an important role in
seismic load distribution in a building.
Consider a RC slab (see figure next slide)



For horizontal loads, it acts as a deep beam with
depth equal to building width, and the beam
width equal to slab thickness.
Being a very deep beam, it does not deform in
its own plane, and it forces the frames/walls to
fulfil the deformation compatibility of no in-plane
deformation of floor.
This is rigid floor diaphragm action.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 95
Concept of Floor
Diaphragm Action
Fig. from Jain S K, “A Proposed Draft for IS:1893…Part II:
Commentary and Examples,” J. of Struct Engg, Vol. 22, No.
2, July 1995, pp 73-90
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 96
Horizontal Distribution... (Cl. 7.7.2) (contd…)

Implications of rigid floor diaphragm action:


In case of symmetrical building and loading, the
seismic forces are shared by different frames or
walls in proportion to their own lateral stiffness.
See figure next slide.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 97
Lateral Load Distribution
Due to Rigid Floor
Diaphragm: Symmetric
Case – No Torsion
Fig. from Jain S K, “A Proposed Draft for IS:1893…Part II:
Commentary and Examples,” J. of Struct Engg, Vol. 22, No.
2, July 1995, pp 73-90
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 98


When building is not symmetrical, the floor
undergoes rigid body translation and rotation.
See figure next slide
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 99
Analysis of Forces Induced
by Twisting Moment (Rigid
Floor Diaphragm)
Fig. from Jain S K, “A Proposed Draft for IS:1893…Part II:
Commentary and Examples,” J. of Struct Engg, Vol. 22, No.
2, July 1995, pp 73-90
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 100
Rigid Diaphragm Action

In-plane rigidity of floors is sometimes misunderstood to
mean that



The beams are infinitely rigid, and
The columns are not free to rotate at their ends.
Rotation of columns is governed by out-of-plane
behaviour of slab and beams.
(a) In-plane floor
deformation, (b) Outof-plane floor
deformation.
Fig. from Jain S K, “A Proposed
Draft for IS:1893…Part II:
Commentary and Examples,” J. of
Struct Engg, Vol. 22, No. 2, July
1995, pp 73-90
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 101
Buildings without Diaphragm Action

When the floor diaphragm does not exist, or
when the diaphragm is extremely flexible as
compared to the vertical elements

The load can be distributed to the vertical
elements in proportion to the tributary mass
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 102
Flexible Floor Diaphragms


There are instances where floor is not rigid.
“Not rigid” does not mean it is completely flexible!


Hence, buildings with flexible floors should be carefully
analyzed considering in-plane floor flexibility.
Note 1 of Cl. 7.7.2.2 gives the criterion on when the
floor diaphragm is not to be treated as rigid.
Definition of Flexible Floor
Diaphragm (Cl. 7.7.2.2)
Fig. from Jain S K, “A Proposed
Draft for IS:1893…Part II:
Commentary and Examples,” J. of
Struct Engg, Vol. 22, No. 2, July
1995, pp 73-90
A. K. Sariar, Shamvwi Const.
(Plan View of Floor)
In-plane flexibility of diaphragm to be considered when
Δ2>1.5{0.5(Δ1+ Δ2)}
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 103
Lateral Load Distribution
Considering Floor Diaphragm
Deformation: Vertical
Analogy Method
Fig. from Jain S K, “A Proposed
Draft for IS:1893…Part II:
Commentary and Examples,” J. of
Struct Engg, Vol. 22, No. 2, July
1995, pp 73-90
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 104
Analysis for Flexible Floor Diaphragm Buildings (contd…)

Alternatively, one can take the design force as
envelop of (that is, the higher of) the two
extreme assumptions, i.e.,


Rigid diaphragm action
No diaphragm action (load distribution in
proportion to tributary mass)
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 105
Requirement of Dynamic Anal. Cl. 7.8.1

Criteria for Dynamic Analysis
Seismic
Zone
Regular
Building
Irregular
Buildings
II
Ht < 15m
For all
Height
III,IV and V For all
building
A. K. Sariar, Shamvwi Const.
For all
building
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 106
Why Dynamic Analysis?

Expressions for design load calculation (cl.
7.6.3) and load distribution with height based
on assumptions


Fundamental mode dominates the response
Mass and stiffness distribution are evenly
distributed with building height

Thus, giving regular mode shape
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 107
Why Dynamic Analysis? (contd…)




In tall buildings, higher modes can be quite
significant.
In irregular buildings, mode shapes may be
quite irregular
Hence, for tall and irregular buildings, dynamic
analysis is recommended.
Note that industrial buildings may have large
spans, large heights, and considerable
irregularities:

These too will require dynamic analysis.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 108
Dynamic Analysis as per Cl. 7.7.5.4



New code gives this method in a more
systematic manner in Cl.7.7.5.4
The analysis procedure is valid when a building
can be modeled as a lumped mass model with
one degree of freedom per floor (see fig. next
slide)
If the building has significant plan irregularity, it
requires three degrees of freedom per floor and
the procedure of Cl. 7.7.5.4 is not valid.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 109
Lumped Mass Model for Cl. 7.7.5.4
X3(t)
X2(t)
X1(t)
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 110
At the end of this section



Dynamic analysis requires considerable skills.
Just because the computer programme can
perform dynamic analysis: it is not sufficient.
One needs to develop in-depth understanding of
dynamic analysis.


There are approximate methods (such as
Rayleigh’s method, Dunkerley’s method) that
one should use to evaluate if the computer
results are right.
It is not uncommon to confuse between the
units of mass and weight when performing
dynamic analysis.

Leads to huge errors.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 111
Bldgs with Soft Storeys Cl. 7.10




Most of the time, soft storey building is also the
weak storey building.
In the code, distinction between soft storey and
weak storey has not been made.
Soft/weak storey buildings are well-known for
poor performance during earthquakes.
In Bhuj earthquake of 2001, most multistorey
buildings that collapsed had soft ground storey.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 112
Bldgs with Soft Storeys Cl. 7.10 (contd…)
Fig from
Murty et al,
2002
Open ground story
Bare frame
Notice that the soft-storey is subject to severe deformation
demands during seismic shaking.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 113
Buildings with Soft Storeys Cl. 7.10 (contd…)


This clause gives two approaches for treatment
of soft storey buildings.
First approach is dynamic analysis considering
B/W and inelstic deformation.





It is a very sophisticated approach.
Based on non-linear analysis.
Code has no specifications for applying this
approach.
Cannot be applied in routine design applications
with current state of the practice in India.
Structural wall density >=2% in both direction.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 114
Deformations Cl. 7.11


For a good seismic performance, a building
needs to have adequate lateral stiffness.
Low lateral stiffness leads to:





Large deformations and strains, and hence more
damage in the event of strong shaking
Significant P-D effect
Damage to non-structural elements due to large
deformations
Discomfort to the occupants during vibrations.
Large deformations may lead to pounding with
adjacent structures.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 115
Deformations Cl. 7.11 (contd…)


Stiff structures, even though attract more
seismic loads, have generally performed better
during past earthquakes.
The current code also restricts inter-storey
displacement to 0.004 times the storey height
under design seismic loads.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 116
Deformations Cl. 7.11 (contd…)

Note that real displacement in a strong shaking
will be much larger than the displacement
calculated for design seismic loads

Because design seismic force is a reduced force.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 117
Computation of Drift

Note that higher the stiffness, lower the drift but
higher the lateral loads. Hence,


For computation of T for seismic design load
assessment, all sources of stiffness (even if
unreliable) should be included.
For computation of drift, all sources of flexibility
(even if unreliable) should be incorporated.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 118
Computation of Drift (contd…)

Thus, in computation of drift:

Stiffness contribution of non-structural elements
and non-seismic elements (i.e., elements not
designed to share the seismic loads) should not
be included.


This is because such elements cannot be relied upon to
provide lateral stiffness at large displacements
All possible sources of flexibility should be
incorporated, e.g., effect of joint rotation,
bending and axial deformations of columns and
shear walls, etc.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 119
Compatibility of Non-Seismic Elements (Cl. 7.11.2)

Important when not all structural elements are
expected to participate in lateral load resistance.


Examples include flat-plate buildings or buildings
with pre-fabricated elements where seismic load
is resisted by shear walls, and columns carry only
gravity loads.
During 1994 Northridge (Calif.) earthquake,
many collapses due to failure of gravity
columns.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 120
Compatibility of Non-Seismic Elements (Cl. 7.11.2) (contd…)



During shaking, gravity columns do not carry
much lateral loads, but deform laterally with the
shear walls due to compatibility imposed by
floor diaphragm (see Fig. next slide)
Moments and shears induced in gravity columns
due to the lateral deformations may cause
collapse if adequate provision not made.
ACI Code for RC design has a separate section
on detailing of gravity columns to safeguard
against this kind of collapse.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 121
Compatibility of Non-Seismic Elements (Cl. 7.11.2) (contd…)
Shear Wall
Fig. V Agrawal
Shear Wall
Floor Slab
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 122
Compatibility of Non-Seismic Elements (Cl. 7.11.2) (contd…)


Since deflections are calculated using design
seismic force (which is a reduced force), the
deflection is to be multiplied by R.
Multiplier R could be debated since it will only
ensure safety against Design Basis Earthquake.

For safety against Maximum Considered
Earthquake, multiplier should be (2R).
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 123
Separation Between Adjacent …Cl. 7.11.3



During seismic shaking, two adjacent units of
the same building, or two adjacent buildings
may hit each other due to lateral displacements
(pounding or hammering).
This clause is meant to safeguard against
pounding.
Multiplication with R is as explained earlier:
since deflection is calculated using design
seismic force which are reduced forces.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 124
Separation Between Adjacent …Cl. 7.11.3 (contd…)


Pounding effect is much more serious if floors of
one building hit at the mid height of columns in
the other building.
Hence, when two units have same floor
elevations, the multiplier is reduced from R to
R/2.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 125
Separation Between Adjacent …Cl. 7.11.3 (contd…)
Potential pounding
location
Building 2
Building 1
a
Potential pounding
location
Building 2
Building 1
b
Pounding in situation (b) is far more damaging.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 126
Foundations Cl. 7.12.1


This is a preventive use of foundation types
vulnerable to differential settlement.
In zones III,IV and V, ties to be provided for
isolated spread footings and for pile caps


Except when footings directly supported on rock
Cl 7.12.1 of the code which states:
Isolated R.C.C. footing without tie beams, or
unreinforced strip foundation shall not be
permitted in soft soils with N<10.

This note is applicable for all seismic zones.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 127
Cantilever Projections Cl. 7.12.2

All projections (vertical and horizontal) are most
vulnerable to damage during earthquakes.


Being cantilevers, there is no redundancy, and
hardly any ductility.
Design of projections for five times the seismic
coefficient.
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 128
Compound Walls Cl. 7.12.3

To be designed for design horizontal coefficient
Ah with I=1 and R=1,S/g=2.5 and Z=1.25Z
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 129
Moment Resisting Frame


Cl. 4.14 defines Ordinary and Special Moment
Resisting Frames.
Ductile structures perform much better during
earthquakes.



Hence, ductile structures are designed for lower
seismic forces than non-ductile structures.
For example, compare the R values in Table 9
IS:13920-2016 provides provisions on ductile
detailing of RC structures for seismic
performance.
A. K. Sariar,Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
General Principles and Design Criteria (Section 6)

Four main sub-sections




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Cl. 6.1: General Principles
Cl. 6.2: Assumptions
Cl. 6.3: Load Combination and Increase in
Permissible Stresses
Cl. 6.4: Design Spectrum
This lecture covers sub-sections: Cl. 6.2 and Cl.
6.3
A. K. Sariar,Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Cl.6.2 Assumptions


Earthquake consists of a number of waves
having different frequency. No Resonance
occurs due to earthquake waves.
There have been instances such as the Mexico
earthquake of 1985 which have violated above
assumption (a).
A. K. Sariar,Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Assumption b)




A strong earthquake takes place infrequently.
A strong wind also takes place infrequently.
Hence, the possibility of strong wind and strong
ground shaking taking place simultaneously is
very very low.
It is common to assume that strong earthquake
shaking and strong wind will not occur
simultaneously.

Same with strong earthquake shaking and
maximum flood.
A. K. Sariar,Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Assumption c) on Modulus of Elasticity


Modulus of elasticity of materials such as
concrete, masonry and soil is difficult to specify
Its value depends on




Stress level
Loading condition (static versus dynamic)
Material strength
Age of material, etc
A. K. Sariar,Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Load Combination 0.9DL 1.5EL


Horizontal loads are reversible in direction.
In many situations, design is governed by effect
of horizontal load minus effect of gravity loads.
In such situations, a load factor higher than 1.0
on gravity loads will be unconservative.
 Hence, a load factor of 0.9 specified on gravity
loads in the combination 4)
Many designs of footings, columns, and positive steel in
beams at the ends in frame structures are governed by
this load combination
Hence, this combination has been made very specific in
IS:1893-2016.



A. K. Sariar,Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Liquefaction Potential



Information given in cl.6.3.5.3 and Table 2 on
Liquefaction Potential is very primitive:
A simplified method is given in Annex F for
determining liquefaction potential analysis.
It is common these days to use SPT or CPT
results for detailed calculations on liquefaction
potential analysis.
A. K. Sariar,Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Moment of Inertia Cl.6.4.3.1



For structural analysis, moment of inertia is
taken as
70% of Igross of Column
35% of Igross of Beam
A. K. Sariar,Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Vertical Acceleration Cl.6.4.6


It is estimated with S/g=2.5
Vertical acceleration has been taken two-third of
horizontal acceleration
A. K. Sariar,Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Equations for Design Spectrum

Equivalent Static Method
A. K. Sariar,Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Equations for Design Spectrum

Dynamic Analysis Method
A. K. Sariar,Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Equations for Design Spectrum

Equivalent Analysis Method
A. K. Sariar,Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Equations for Design Spectrum

Dynamic Analysis Method
A. K. Sariar,Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Thank you
A. K. Sariar, Shamvwi Const.
Presentation on IS:1893:2016 / Oct. 2019
Lecture 1 / slide 143