Essentials of Earthquake Engineering for Architects and Engineers

1. Essentials of Earthquake
Engineering for Architects and
Engineers
Architect's and Engineer's Meet at Patiala
27th Aug. 2007
Dr. Hardeep Singh Rai
Professor and Head, Civil Engg. Dept.
Guru Nanak Dev Engg. College ­ Ludhiana

2. Agenda:
Vulnerable environment
●
Govt's role
●
Professional's role
●
Planning
●
Design
●
Construction
●

3. India
One of the most disaster prone countries
●
85% area is vulnerable to one or multiple
●
disasters
57% area is in high seismic zone
●

4. Govt's contribution
Prepration of standards
●
IS 1893: Criteria for Earthquake Resistant
●
Design of Structures
1962: `Recommendations for Earthquake
–
Resistant Design of Structures'
Revised in 1966, 1970, 1975, 1984
–
2002: (Part 1) General provisions and
●
Buildings; 2005 (4) Industrial Structures
Including Stack Like Structures

5. Govt's contribution (contd.)
Part 2: Liquid Retaining Tanks – Elevated
●
and Ground Supported
Part 3: Bridges and Retaining Walls
●
Part 5: Dams and Embankments
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IS 4326:1993 Earthquake Resistant Design
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and Construction of Buildings ­ Code of
Practice

6. Govt's contribution (contd.)
IS 13828:1993 Improving Earthquake
●
Resistance of Low Strength Masonry
Buildings – Guidelines
IS 13920:1993 Ductile Detailing of
●
Reinforced Concrete Structures Subjected to
Seismic Forces – Code of Practice
IS 13935:1993 Repair and Seismic
●
Strengthening of Buildings – Guidelines

7. IS: 4326 Eq. Res. D&C bldgs CP
General Principles:
●
Lightness
–
Continuity of constrction
–
Projecting and suspended parts
–
Configuration
–
Strength in various directions
–
Foundations
–
Ductility
–
Damage to non­structural parts
–
Fire safety
–

8. Affect of Architectural Features on Bld during EQ
Size of the Building


9. Affect of Architectural Features on Bld during EQ
* If we have a poor configuration to start with, all
the engineer can do is to provide a band­aid –
improve a basically poor solution as best as
he can. Conversely, if we start­off with a
good configuration and reasonable framing
system, even a poor engineer cannot harm its
ultimate performance too much.
­­ Henry Degenkolb

10. Affect of Architectural Features on Bld during EQ
Horizontal layout of the building


11. Affect of Architectural Features on Bld during EQ
Vertical layout of buildings


12. Affect of Architectural Features on Bld during EQ
Adjacency of Buildings


16. What are the Seismic Effects on Structure
Horizontal and Vertical Shaking


18. Affect of Architectural Features on Bld during EQ
Suggestions

Architectural features detrimental to EQ response of building
●
should be avoided. If not they must be minimised
In case irregular features included in building higher level of
●
engineering efforts is required in structural design
Decision made at the planning stage on building configuration are
●
very important
Building with simple architectural feature will always behave
●
better during EQ

19. How building twists during Earthquake
Contd………

20. Seismic Design Philosophy for Building
Severity of ground shaking at a given location
during an earthquake can be minor, moderate and
strong.
Relatively speaking, minor shaking occurs
frequently, moderate shaking occasionally and
strong shaking rarely.
 For instance, on average annually about 800
earthquakes of magnitude 5.0­5.9 occur in the world
while the number is only about 18 for magnitude
range 7.0­7.9

21. Seismic Design Philosophy for Building
• Don’t attempt to make EQ proof building (Bld. Will be too
robust and too expensive)
• Engineering intention shall be to make EQ resistant building

22. Seismic Design Philosophy for Building
Earthquake Design Philosophy


23. Seismic Design Philosophy for Building
Earthquake Resistant Design


24. Seismic Design Philosophy for Building
Acceptable Damage:Ductility


25. Behaviour of Brick Masonary Houses during EQ
Behaviour of Wall

• Masonary Bld. Most vulnerable under EQ
shaking(Brittle Structure)
• Wall is most vulnerable component of the
Bld due to horizontal force (EQ)
• Wall offers greater resistance if pushed
along its length (Strong Direction)
• Wall topples easily if pushed in a direction
perpendicular to its plan(Weak Direction)

26. Behaviour of Brick Masonary Houses during EQ
Behaviour of Wall

• All walls if joined properly to the adjacent
wall ensures good seismic performance
• Walls loaded in weak direction take
advantage of the good lateral resistance
offered in their strong direction
• Walls need to be tied to the roof and
foundation to reserve their overall integrity

27. Simple Structural Configuration required for Masonary
Building
Box Action in Masonary Bld.

• Separate block can oscillate independently
and even hammer each other (If too close
during EQ)
• Adequate gap required betn such blocks
• Gap not necessary if horizontal projections
in Bld are small
• An integrally connected inclined stair case
slab acts like a cross brace betn floors
• It transfers large horizontal forces at the roof
and the lower level (Area of Potential
Damage)

28. Vertical Band necessary in Masonary Building
Protection of Opening in Walls

•Most common damage observed after an EQ
is diagonal X­cracking of wall pier, inclined
cracks at corners of doors and window
opening.
• A square opening become rhombus during
EQ Shaking
• The corners that come closer develop cracks,
Cracks are bigger when the opening sizes are
large
•Steel bars provided all around the opening
restrict cracks (corner)

29. Seismic Design Philosophy for Building
EQ Resistant Design of Building


30. Effect of Earth Quake on RC Building
Strength Hierarchy

• If this strategy adopted in design & beam detailing done properly
­ Building as a whole can deform by large amount despite
progressive damage caused due to consequent yielding of beams ­ If
columns are made weaker, it suffer local damage at the top and bottom
of a particular storey
• This localised damaged can lead to
collapse of building

31. How do Beams in RC Bld resist EQ
Reinforcement and Seismic Damage

• Long straight bars (longitudinal bars) placed along its length
• Closed loop of small diameter steel bars (Stirrups) placed vertical at
regular intervals along its length

32. How do Beams in RC Bld resist EQ
Reinforcement and Seismic Damage

• Two basic types of failure in beams:­
a) Flexural (Bending) failure
b) Shear failure

33. How do Beams in RC Bld resist EQ
Reinforcement and Seismic Damage

• FLEXURAL (BENDING) FAILURE
• Beam can fail in two ways
a) Brittle failure (b) Ductile failure
• Brittle Failure:­
Relatively more steel is present on
the tension face, concrete
crushes in compression which is
undesirable

34. How do Beams in RC Bld resist EQ
Reinforcement and Seismic Damage

• Ductile Failure:­
Relatively less steel is present on
the tension face, steel yield first
and the re distribution occurs in the
beam until eventually concrete
crushes in compression, is
desirable
• Characterised with many vertical
cracks starting from the stretched beam
face and going towards its mid depth

35. How do Beams in RC Bld resist EQ
Reinforcement and Seismic Damage

• SHEAR FAILURE:­­
­ A shear crack, inclined at 45
degree to the horizontal, develops
at mid depth near the support and
grows towards the top and bottom
face
­ Closed loop stirrups are provided
to avoid such shearing action
­ Shear damage occurs when area
of shear stirrup is insufficient
­ A Brittle failure, must be avoided

36. How do Beams in RC Bld resist EQ
Stirrup helps beam in three ways

• It carries the vertical shear force, thereby resist diagonal shear
crack
• It protect the concrete from buldging outwards due to flexure
• It prevents the buckling of compressed longitudinal bars due to
flexure

37. How do Beams in RC Bld resist EQ
Longitudinal bars

• Provided to resist flexural cracking on the side of the beam that
stretches
• Requires on both faces at the ends and on the bottom face at mid
length

38. How do Beams in RC Bld resist EQ
Longitudinal bars

• As per ductile detailing code:­­
­ At least two bars shall go through the full length of the beam at
the top as well as the bottom of the beam
­ At the end of the beams, the amount of steel provided at the
bottom is at least half that at the top

39. How do Beams in RC Bld resist EQ
Requirements related to stirrups in RC Beams

• Φof Stirrups – 6 mm minimum
• Φ o
f Stirrups – 8 mm , if beam>5m.
• Both ends of a vertical stirrups should
be bent into 135 degree hook and extend
sufficiently beyond this hook to ensure
that stirrups does not open out in an
earthquake

40. How do Beams in RC Bld resist EQ
Requirements related to stirrups in RC Beams

• Max. spacing of stirrups is less than half
the depth of beam
• For a length twice the depth of beam
from the face of the column, the spacing
should not be more than one fourth the
depth of beam

41. How do Beams in RC Bld resist EQ
Requirements related to stirrups in RC Beams

• At the location of the lap, the bars
transfer large forces from one to another
• Laps of the longitudinal bars are:­
a) Made away from the face of col.
b) Not made at locations where they are
likely to stretch by large amounts and
yield (eg. Bottom bars at mid length of
the beam)
• At the location of laps, vertical stirrups should be provided at closer
spacing

42. How do Columns in RC Bld resist EQ
Possible EQ Damage

• Column can sustain 2 type of damage:­
a) Axial Flexural (Combined Comp.
Bending) failure
b) Shear Failure (Brittle Damage) &
must be avoided by providing transverse
ties at closer spacing
• Minimum width of the column = 300
mm, and if the unsupported length of
column <4 meter and beam length< 5
m., width up to 200 mm is allowed

43. How do Columns in RC Bld resist EQ
Possible EQ Damage

• Purpose of horizontal ties
a) Carry horizontal shear force induced
by EQ and thereby to resist diagonal
shear crack
b) Hold together the vertical bars and
prevent them from buckling
c) Contain the concrete in the column
within the closed loops
• The ends of the ties must be bent as 135
degree. The length of the ties
beyond hook bend must be atleast 10d of steel bar ( close ties) but
not less than 75 mm.

44. How do Columns in RC Bld resist EQ
Possible EQ Damage

• In column where spacing between the
corner bar exceeds 300 mm
“Additional links with 180 hook ends
for ties to be effective in holding the
concrete in its place and to prevent the
buckling of vertical bars”

45. How do Beam Column Joins in RC bld Resist EQ
EQ behaviour of Joints

• Column beam joint have limited
force carrying capacity when forces
larger than these are applied during
EQ, joints are severely damaged
• Repairing damage joints is difficult,
so damage must be avoided
• Under EQ shaking, the beam adjoining a joint are subjected to
moments in the same direction

46. How do Beam Column Joins in RC bld Resist EQ
EQ behaviour of Joints

Under these moments, the top bar in the
beam­column joint are pulled in one
direction & the bottom one in opposite
direction.
The forces are balanced by bond stress
developed between concrete and steel in
the joint region
If there is insufficient grip of concrete
on steel bars in such circumstances, the
bar slip inside the joint region, the beam
loose their capacity to carry load

47. How do Beam Column Joins in RC bld Resist EQ
EQ behaviour of Joints

 Under this pull­ push forces at
top and bottom ends joint undergo
geometric distortion
 One diagonal length of the joint
elongates and the other compresses. If
the column cross­ sectional size is
insufficient, the concrete in the joint
develops diagonal cracks

48. How do Beam Column Joins in RC bld Resist EQ
EQ behaviour of Joints

 Problem of diagonal cracking &
crushing of concrete in the joint region
can be controlled by
a) Providing large column size
b) Providing closely spaced closed loop
steel ties around column bars in joint
region
Ties hold together the concrete in the
joint and also resist shear force.

49. How do Beam Column Joins in RC bld Resist EQ

50. How do Beam Column Joins in RC bld Resist EQ
 Anchorage of beam bars in
exterior joints
 Anchorage of beam bars in
interior joints

51. Why are Soft storey building vulnerable in EQ

52. Why are Soft storey building vulnerable in EQ

53. Why are Soft storey building vulnerable in EQ

54. Why are Soft storey building vulnerable in EQ

55. Why are Short Columns more Damaged During EQ
Short Column Behaviour

 Bld resting on sloped ground consisting of short &
long column, when shakes, all column move horizontally
by the same amount along with floor slab at a particular
level
 Short column effect also
occurs in columns that support
mezzanine floor or loft slabs that
are added in between two regular
floors.

56. Why are Short Columns more Damaged During EQ
Short Column Behaviour

 A tall column & a short column of
same cross section move horizontally by
same amount during EQ
 Short column is stiffer than long
column(Stiffness of column means
resistance to the deformation)
 Larger is the stiffness, larger is the
force required to deform it

57. Why are Short Columns more Damaged During EQ
Short Column Behaviour

 If a short column is not adequately designed for such
large force, it can suffer significant damage during EQ
 Short column attracts several times larger force and
suffer more damage as compare to taller ones.
 This behaviour of short
column is called short column
effect and often the damage is
in the form of X –shaped
cracking (Shear Failure)

58. Why are Short Columns more Damaged During EQ
Short Column Behaviour

 Special Confining reinforcement is
to be provided over the full height of
column that are likely to sustain short
column effect
 Special confining reinforcement
must extend beyond the short column
into the column vertically above and
below by certain distance

59. Why are Short Columns more Damaged During EQ
The Solution

 In new building, short column effect should be
avoided to the extent possible during Architectural design
itself
For short columns in the existing building retrofit solutions
can be employed to avoid damage in future
Earth Quake
The retrofit solution should be designed by a Qualified
structural Engineer with requisite background

60. How to reduce EQ effects on Buildings
Why EQ effects are to be reduced

 Lifeline structures like hospitals etc are remain to be functional
in the aftermath of EQ
Special techniques are required to design such life line structures
which usually cost more than normal bld do
Two basic technology are
a) Base isolation device
b) Seismic Dampers

61. How to reduce EQ effects on Buildings
Why EQ effects are to be reduced

a) Base isolation device
­ Idea behind base isolation is to detach (isolate) the buildings
from the ground in such a way that EQ motions are not transmitted
up through the building or at least reduced
b) Seismic Dampers
­ Special devices introduced in the building to absorb the
energy provided by the ground motion to the building

62. How to reduce EQ effects on Building
Base isolation in real buildings

• Over 1000 blds across the world have been equipped with seismic
base isolation
• In India base isolation technique was
first demonstrated after 1993 Killari
EQ
• Two single storey bld (one school and
another shopping complex bld) were
built with rubber base isolators resting
on hard ground
• The four storey bhuj hospital bld was
built with base isolation technique
after 2001 bhuj EQ

63. How to reduce EQ effects on Building
Seismic Dampers

• Another approach for controlling seismic
damage in bld is by installing seismic
dampers in place of structural elements
such as diagonal braces
• These dampers act like hydraulic shock
absorbers and absorbs part of the seismic
energy transmitted through them, thus
damps the motion of the building

64. Resource Material
EERI, (1999), Lessons Learnt Over Time – Learning from
Earthquakes Series: Volume II Innovative Recovery in India,
Earthquake Engineering Research Institute, Oakland (CA), USA;
also available at
http://www.nicee.org/readings/EERI_Report.htm.
Hanson,R.D., and Soong,T.T., (2001), Seismic Design with
Supplemental Energy Dissipation Devices, Earthquake
Engineering Research Institute, Oakland (CA), USA.
Skinner,R.I., Robinson,W.H., and McVerry,G.H., (1999), An
Introduction to Seismic Isolation, John Wiley & Sons, New
York.
IITK & BMTPC Earthquake Tips; available at
http://www.nicee.org/

65. For a Building to Perform well
in an Earthquake it should
have Six main attributes
Lightness
●
Simple and Regular Configuration
●
Adequate Lateral strength
●
Stiffness
●
Continuity of Construction
●
Ductility
●

66. Contact:
Email:
●
hardeep . rai @ gmail . com
–
hsrai @ gndec . ac . in
–
hs @ raiandrai . com
–
hsrai @ yahoo . com
–
hsrai @ grex . org
–
hsrai @ gmx . net
–

67. Thank you.