CODE OF PRACTICE ON EARTHQUAKE
RESISTANT DESIGN OF BUILDINGS:
AN OVERVIEW
Dr. D.K. Paul
Chairman, Earthquake Engineering Sectional Committee CED 39;
R td Professor,
Retd.
P f
Dept.
D t off Earthquake
E th
k Engineering.,
E i
i
IIT Roorkee
R k
1
MESSINA, ITALY EARTHQUAKE
OF DEC.
DEC 28,
28 1908
¾
Death toll: 83,000 - greatest among European
earthquake
¾
Government of Italy appointed a special Committee
consisting of 5 professors of engineering and 9
practicing engineers to study the earthquake and
make recommendations
¾
Structures be
S
b designed
d i
db
by means off equivalent
i l
static
i
lateral load method (%g) – M. Panetti, Prof. of Applied
M h i ”
Mechanics”
¾
First engineering recommendation for ERD of building
¾
2
The idea soon spread to the world
¾
O January
On
Ja ua y 1,, 1943
9 3 tthe
e ccity
ty o
of Los
os Angeles
ge es cchanged
a ged
earthquake safety requirement
¾
So that seismic coefficient varied along the height of
building and was also a function of total height ( i.e.
period of structure)
¾
First time building code considered the flexibility and
the mass of the structure
`
3
BACKGROUND ON ERD&C CODES
BIS 55 years ago brought out, for the first time, Code IS:1893-1962
"Recommendation for ERD of Structures".
`
This Standard was subsequently revised in 1966, 1970, 1975, 1984,
2002 and recently 2016.
Fourth revision in 1984 renamed as “Criteria for ERD of structures”
and the fifth revision in 2002 the code was split in five parts
¾
IS 4326-1967
4326 1967 “ ERD and Construction of Buildings”
Buildings Revised in
1976, included some details for achieving ductility in reinforced
concrete buildings . Further revisions were made In 1993 and 2013
¾
In 1993 a separate code IS 13920 was brought out which was
devoted on ductile design and detailing, and recently revised in 2016
4
RECENT
C
REVISION
S O OF
O CODES
CO S
`
Recently, the Code on "Criterion for Earthquake
R i t t Design
Resistant
D i off Structures”
St
t
” IS 1893:
1893 2016 P
Partt 1
is revised sixth time and
`
the first revision of code on “Ductile Design and
Detailing of Reinforced Concrete Structures
Subjected to Seismic Forces”
Forces IS 13920: 2016 has
been brought out with significant modifications
`
The National Building Code of India 2016 (NBC 2016)
is a comprehensive building Code, has also been revised
recently. It also includes the provisions for safety of
buildings against earthquakes
5
REVISION OF CODES
`
R&D
& in tthe
ea
area
ea o
of Earthquake
a t qua e Engineering
g ee g have
a e made
ade
huge stride
`
R&D reflecting the current state of knowledge and
relevant International practices find its way in updating
Codal Practices
`
Studyy of p
performance of buildings/
g structures during
gp
past
earthquakes provide valuable data in upgrading the
Codes
`
Experimental investigations carried out on specific issues
in labs also provide useful data for Code up
up-gradation
gradation
6
ACQUAINTING
CQU
G NEW PROVISIONS
O SO S
`
Se s c sa
Seismic
safety
ety o
of bu
buildings
d gs is
s ac
achieved
e ed by implementing
pe e t g
and enforcing current Seismic Codes
`
Practicing Engineers and Architects have to acquaint
themselves with the new provisions of the revised
Codes
`
The adoption and enforcement of revised building Codes
with clear understanding of the provisions is utmost
important
This presentation gives a brief overview of the new and
p
in Codal p
provisions
future developments
7
SEISMIC SAFETY OF BUILDINGS
¾
¾
Conventional Earthquake
q
Resistant Design
g
Non-Conventional Design based on either reduction
or absorption of e/q forces
- Seismic Base Isolation
- Control Devices
¾
Passive control devices (Energy absorbing/ diverting
devices)
¾
¾
¾
¾
¾
Passive energy dissipation devices (Viscous dampers)
Seismic base isolation devices (Elastomeric bearing
bearing, Sliding
Bearing)
Active control systems (Dynamic Intelligent Building – DIB)
Semi--active control systems
Semi
Hybrid control systems
- Energy Absorbing Devices
8
INDIAN STANDARD CODES OF PRACTICE
1. IS: 1893-2016 Criteria for earthquake resistant design of structures
((Parts 1-5))
2. IS: 4326-2013 Code of practice for earthquake resistant design
and construction of buildings
3. IS: 13827-1993 Guidelines for improving earthquake resistance of
earthen buildings
4 IS: 13828
4.
13828-1993
1993 Guidelines for improving earthquake resistance of
low strength masonry
practice for ductile design
g and detailing
g of
5. IS: 13920-2016 Code of p
reinforced concrete structures subjected to seismic forces
6. IS: 13935-2009 Guidelines for repair and seismic strengthening of
buildings
7. IS: 15988:2013 Guidelines for seismic evaluation and
strengthening of existing reinforced concrete buildings
9
8. IS 1893 (Part 2): 2014 ‘Criteria for earthquake resistant
design of structures : Liquid retaining tanks’
9. IS 1893 (Part 3): 2014 ‘Criteria for earthquake resistant
design of structures : Bridges and retaining walls’
10. IS 1893 (Part 4): 2015 First Revision, ‘Criteria for
earthquake resistant design of structures : Industrial
structures including stack like structures‘
11. IS 4967: 1968 Recommendations for seismic
instrumentation for river valley projects
12 IS 4991: 1968 Criteria for blast resistant design of
12.
structures for explosions above ground
13 IS 6922: 1973 Criteria for safety and design of structures
13.
subject to underground blasts
10
DEVELOPMENT OF NEW CODES ..1
14.
IS 1893 (Part 5) ‘Criteria for earthquake resistant design of
Dams and Embankments : Part 5 Dams’
Sec 1: Earth embankments and small to intermediate size
earth and rock fill dams
Sec 2: Concrete Gravity Dams
11
15.
Guidelines for Risk Reduction for Structure Against
Tsunami
16.
Probabilistic Seismic Hazard Map of India (PSHA)
DEVELOPMENT OF NEW CODES…2
12
17
17.
Pre Earthquake Safety Assessment of Structures − RC
Pre-Earthquake
Buildings
18
18.
S i i R
Seismic
Retrofit
t fit off St
Structures
t
− Masonry
M
Buildings
B ildi
19.
Seismic Design
g and Ductile Detailing
g of Steel Buildings
g –
Code of Practice
20.
Post-Earthquake Damage Assessment of Structural
Elements (SEs) − Bridges (RC, Masonry and Steel)
21.
Post-Earthquake Damage Assessment of SEs − Water
Tanks (Elevated and Ground Supported)
DEVELOPMENT OF NEW CODES..3
13
22.
Post-Earthquake Damage Assessment of SEs −
Pipelines
23.
Post-Earthquake Damage Assessment of SEs −
Communication Towers
24.
Post-Earthquake Damage Assessment of SEs −
Non-Structural
S
Elements
25
25.
Post-Earthquake
Post
Earthquake Damage Assessment of SEs Coastal Structures
DEVELOPMENT OF NEW CODES..4
14
26.
Performance Based Seismic Design & Retrofitting
27.
Guidelines for Development of Seismic Microzonation
28
28.
Seismic Base Isolation & Energy Absorption Devices
29
29.
Liquefaction Potential of Soils During Earthquakes
30.
Seismic Qualification of Equipment
31.
Seismic Design of Buried Pipelines - Code of Practice
RECENT REVISION OF CODES
`
Revision
R
i i off IS 1893 (Part
(P t 1) Sixth
Si th Revision,
R i i
'Criteria
'C it i for
f earthquake
th
k
resistant design of structures: Part 1 General provisions and
Buildings’ 2016
`
Revision of IS 13920 ‘Ductile Detailing of Reinforced Concrete
j
to seismic forces – Code of Practice ((2016))
Structures subjected
`
Revision of IS 4326 ‘Code of practice for earthquake resistant design
and construction of buildings’
buildings (2013)
`
Revision of IS 1893 (Part 4) First Revision, ‘Criteria for earthquake
resistant design of structures : Part 4 Industrial structures including
stack like structures‘ (2015)
15
IMPORTANT REVISIONS INCORPORATED IN
IS 1893 PART 1: 2016 (SIXTH REV.)….1
¾ Design spectra defined up to natural period 6.00 s
¾ Same design spectra corresponding to 5% damping
are specified for all buildings, irrespective of material
of construction
¾ Introduced intermediate importance category of
buildings to consider the density of occupancy
¾ Temporary structures have been covered
¾ Ap
provision is ensured that all buildings
g are designed
g
for at least for a prescribed minimum lateral force
16
IMPORTANT REVISIONS INCORPORATED IN
IS 1893 PART 1: 2016 (SIXTH REV.)…..2
¾ Additional clarity about different types of irregularity of
structural system
¾ Effect of masonry infill walls included
¾ Natural period of buildings with basement, step back
buildings and buildings on hill slopes included
g are introduced
¾ Flat slab buildings
¾ Simplified method is introduced for liquefaction
potential analysis
p
y
17
IMPORTANT REVISIONS INCORPORATED IN
IS 13920: 2016 (FIFTH REV.)…..1
¾ Column to beam strength ratio provision added in
keeping with the strong column-weak beam design
philosophy for moment resisting frames
¾ Shear design of beam-column joints
¾P
Provisions
i i
on d
design
i and
dd
detailing
t ili off b
beams and
d
columns as given in IS 4326:1976 are revised with an
aim to provide them with
adequate stiffness,
strength and
ductility
18
tto make
k them
th
to
t undertake
d t k inelastic
i l ti deformation
d f
ti and
d
dissipating seismic energy
IMPORTANT REVISIONS INCORPORATED IN
IS 13920: 2016 (FIFTH REV.)…..2
¾ For members subjected to axial load and bending
moment, provisions are included for
(i) location
l
ti off llap splices;
li
(ii) calculation of seismic design for shear force of
structural
t t l wall;
ll
(iii) special confining reinforcement in regions of columns
that are expected to undergo cyclic inelastic
deformation.
19
ESTIMATION OF SEISMIC FORCE
20
ESTIMATION OF SEISMIC COEFFICIENT
¾
Seismic Zoning Map
¾
Peak Ground Acceleration (PGA) Contour Map (PSHA)
Currentt trend
C
t d world
ld wide
id iis tto specify
if th
the ground
d
acceleration that has a certain probability of being
exceeded
d d iin a given
i
number
b off years.
It is under development with 2% probability of
exceedance in 50 years (Return period ~ 2500 years)
on B-type sites
21
SEISMIC ZONE MAP
¾ The zoning map is based on expected maximum
seismic intensity in a region
¾ The country has been divided into following four
Zones,
Zone
22
Intensity
Zone Factor
V
>IX
0 36
0.36
IV
VIII
0.24
III
VII
0.16
II
VI
0 10
0.10
PRESENTATION
Int.
23
Z
VI
0.10
VII
0.16
VIII
0.24
> IX
0.36
DESIGN RESPONSE SPECTRA
3.0
Type I: Rock or Hard Soil
2.5
Type II: Medium Soil
Type III: Soft Soil
Sa/g
2.0
1.5
Spectra for Equivalent Static Method
1.0
05
0.5
0.0
0
1
2
3
4
5
6
Natural Period T (s)
3.0
Type I: Rock or Hard Soil
2.5
Type II: Medium Soil
Type III: Soft Soil
Sa/g
2.0
1.5
Spectra for Response Spectra Method
1.0
0.5
0.0
0
1
2
3
Natural Period T (s)
24
4
5
6
Design Horizontal Seismic Coefficient
( Z / 2)( S a / g )
Ah =
(R / I )
p
Z = Zone factor,, refers to zero period
acceleration value. Country has been
divided into four Zones
S a / g = Design acceleration coefficient for
different soil type and natural time
period
i d off b
building
ildi normalized
li d tto PGA
I = Importance factor depending upon
functional use of the structure
R = Response reduction function
depending on the ductility
25
PGA Contours with 2%
probability of
exceedance in 50 years
(Return period ~ 2500
yyears)) on A-type
yp sites
26
5% DAMPING IRRESPECTIVE OF MATERAIL
(Clause 7.2.4)
The value of damping shall be taken as 5 percent of critical
damping for the purposes of estimating in the Design Lateral
Force of a building irrespective of the material of
construction
t ti (namely
(
l steel,
t l reinforced
i f
d concrete,
t masonry, or
a combination thereof of these three basic materials).
This is primarily because the buildings experience inelastic
deformations under design level earthquake effects, resulting
in much higher
g
energy
gy dissipation
p
than that due to initial
structural damping in buildings.
This value of damping shall be used,
used irrespective of the
method of the structural analysis employed, namely
Equivalent Static Method or Dynamic Analysis Method
27
DESIGN LATERAL FORCE
Buildings
g shall be designed
g
for the design
g lateral force
VB ggiven byy
VB = Ah W
Buildings should be designed for at least for Minimum Design
Earthquake Horizontal Lateral Force (Clause 7.2.2)
Seismic Zone
(1)
II
III
IV
V
Percent
H ≤ 120 m
(2)
0.7
1.1
1.6
2.4
SIMPLIFIED PROCEDURE FOR EVALUATION
OF LIQUEFACTION POTENTIAL
`
Based on SPT values
Evaluate SPT blow count N60 for a hammer efficiency of 60%
60%. For non
standard equipment, N 60 shall be obtained using measured value (N)
where
C
(N1 )60 = C N N 60
Pa
CN =
≤ 1 .7
σ ' vo
⎛a
CSR = 0.65⎜⎜ max
⎝ g
`
`
= C
N 60 = NC 60
⎞⎛ σ vo
⎟⎟⎜⎜
⎠⎝ σ ' vo
60
⎞
⎟⎟rd
⎠
CRR
FS =
CSR
Based on CPT values
Based on Shear wave velocity
29
HT
C
HW
C
SS
C
RL
C
CRR 7.5
BD
ASSESSMENT OF LIQUEFACTION
POTENTIAL
(i)
Relation between CRR and (N1)60
for sand for Mw 7.5 earthquakes
(ii)
Relation between CRR and (qc1N)cs
for Mw 7.5 earthquakes
(iii) Relation between CRR and Vs1 for
Mw 7.5 earthquakes
30
CODAL DESIGN PHILOSOPHY
•
Forced Based Design
- Elastic Analysis
y
•
Displacement Based Design
- Performance Based Inelastic Analysis
31
FROM FORCE BASED DESIGN TO
DISPLACEMENT BASED DESIGN
32
F
Fel = qF
Fy
Structures to remain elastic in
major earthquakes is likely to be
uneconomical – force demand is
likely to be high
Fy
xy
xmax = μ x y
x
More economical design can be
achieved by making use of the
ductility of the structure and
over-strength to reduce the
force demand
Equivalent of Ductility and Behaviour Factor with
Equal Elastic and Inelastic Displacement
33
FORCE LEVEL
eight of structu
ure)
(as a fraction of we
1.00
1. REALISTIC FORCE LEVEL FOR MAJOR EARTHQUAKE IN HIGH SEISMIC ZONE
0.80
2. DESIGN FORCE LEVEL ASSUMING RESPONSE REDUCTION FACTOR R=3
0.60
3. REALISTIC FORCE LEVEL FOR LOW-MODERATE
EARTHQUAKE IN HIGH SEISMIC ZONE
0.40
4. EARLY (pre-1971)CODE DESIGN FORCES
0.20
0.00
0.5
1.0
1.5
2.0
2.5
PERIOD (seconds)
34
3.0
3.5
4.0
FORCED BASED ELASTIC DESIGN
•
Elastic design for very high lateral forces due to a major
earthquake would be very uneconomical
•
An economically acceptable design under severe earthquake
can be
b achieved
hi
d by
b allowing
ll i
structure
t t
t undergo
to
d
li it d
limited
damage without collapse
•
The most acceptable approach would be to design structures
to resist most frequent moderate earthquake and
•
then check the resistance for infrequent
q
most severe
earthquake allowing limited damage without collapse which
may occur in useful life time of a structure
•
To account
acco nt for ductility
d ctilit as above,
abo e the elastic average
a erage spectra is
reduced by a Reduction Factor
35
LIMITATIONS OF FORCE-BASED
FORCE BASED
DESIGN METHOD
¾
There is no way to ascertain the performance of Force
Base designed building under severe earthquakes
¾
Force is a poor indicator of damage; rather,
di l
displacement
t is
i b
better
tt iindicator
di t off d
damage
¾
The assumption of constant stiffness is misleading
misleading.
Stiffness varies with strength
¾
Code stipulates a Collapse Prevention performance
under severe earthquake, but we need higher level of
performance for hospitals
p
p
36
ADEQUACY OF FORCE-BASED DESIGN
(FBD) METHOD FOR HOSPITALS
¾ IS Codes and Some International codes specify an
importance factor of 1.5 for hospital buildings
¾ It is
i nott known
k
whether
h th such
h iincrease off fforces gives
i
required performance level of hospitals
¾ O
One way off checking
h ki this
thi iis d
designing
i i h
hospitals
it l b
by
increasing design forces by increasing the Importance
Factor and checking the performance of the same under
Spectrum Compatible Ground Motions scaled to MCE
level
37
COMMENTS ON RESULTS OF FBD
• IO at member level may be achieved with higher
design force level
• But Inter-storey drift ratio remains too high to be
useful for hospital building
• With very high Importance Factor design may
become uneconomical
• The value of Importance Factor cannot be predicted
by any theoretical treatment. Member sizes cannot
be predicted theoretically
Sheear Base (V
Vb)
Building Damage States
Capacity Curve
Collapse
Yield
point
Damage Control
Limited Safety
Displacement
Immediate Occupancy
Level
Life Safety
Level
Structural Stability
Level
Performance Level
Capacity Curve for Nonlinear Structure and Associated Damage States.
39
Base Shear
B
PUSHOVER CURVE AND PERFORMANCE LEVELS
IO
CP
LS
Damage control
Limited Safety
y
Roof displacement
p
Capacity curve
40
DISPLACEMENT-BASED DESIGN
Displacement based design considers the displacement
as the basic design parameter. The strength is obtained
as by product in the design procedure.
procedure Steps are:
1. Design earthquake is represented in terms of
displacement response spectra.
spectra Preliminary design is
done
2 Modal properties found out.
2.
out Design criteria are set in
terms of storey drift index
3 Maximum allowable time period or minimum stiffness is
3.
worked out
4 Minimum required strength of structure is found from
4.
modified spectra
41
PERFORMANCE-BASED DESIGN
Performance-based design is defined as a design to reliably
achieve targeted performance of the structure under given
earthquake hazard
Steps in PBD
1. Setting performance goals
2 Setting performance criteria
2.
3. Defining hazard level
4 Structural design using engineering approach
4.
5. Assuring performance of Operational and Functional
Components
p
((OFCs))
42
THE CLIENT / DESIGNER CAN ASCERTAIN THE
EXPECTED PERFORMANCE OF BUILDING UNDER
DESIGN EARTHQUAKE AND THEREFORE CAN
DECIDE ABOUT THE LEVEL OF SAFETY AND
ECONOMY OF THE STRUCTURE MUCH BETTER.
43
SUMMAY
1 India
1.
I di was among the
th first
fi t few
f
countries
t i in
i the
th world
ld
that brought out the Code of Practice on Earthquake
Resistant Design
2. The Indian Codes of Practice on Earthquake
Resistant Design
g and Construction are abreast with
the latest in the World
3. Codes are developed
p
with the active p
participation
p
from all the stake holders and relevant international
practices
4. Codes on new subjects are taken up whenever need
is felt
44
Thanks
45