2. BHUJ EARTHQUAKE
• A massive earthquake of magnitude 6.9 (on Richter
Scale) occurred on 26th January,2001
• The epicenter of this earthquake was located near
Bhachau (latitude 23.40 N and longitude 70.28E)
• Focal depth of the same was 25 km and radius of
fault area = 23 km.
• As per USGS the source parameters were latitude
23.41 N and longitude 70.23E and focal depth of
16 km.
• The event was subsequently termed as Bhuj
Earthquake or Kutch Earthquake
3. Areas Affected and Damage Caused
• The earthquake ranks as one of the most
destructive events recorded in India.
• It had caused huge damage to infrastructure
and huge death toll.
• The major cities affected were
BHUJ,ANJAR,BHACHAU,GANDHIDHAM,KANDL
A PORT,MORBI,AHMEDABAD, RAJKOT,etc.
4.
5. REINFIRCED CONCRETE BUILDING
CONSTRUCTION PRACTICES
• RC construction is the most common type of
construction in the major cities of Gujarat.
• The buildings are in the range of G+4 to G+10 storey
height.
• The building frame is moment resisting, consisting of
RC slabs cast monolithically with beams and columns
on shallow isolated footings.
• The upper floors are generally constructed with infill
walls made of un reinforced bricks.
• The ground floor is often used for commercial and
parking purposes without the infill walls, resulting in
SOFT or WEAK STORIES.
6.
7. • Most of the buildings have overhanging covered
balconies of about 1.5 m span on higher floors.
• The architects often erect a heavy beam from the
exterior column of the building to the end of the
balcony on the first floor onwards.
• A peripheral beam is provided at the end of the
erected girder to create more parking spaces at
ground floor and allowing more spaces on the upper
floors.
• The upper floor balconies are then constructed on
the peripheral beam.
• The dynamic analysis show that such buildings
vibrate in tensional mode , which is undesireable.
8.
9. IDENTIFICATION OF DAMAGES IN RC
BUILDINGS
• The buildings in Bhuj have been damaged due
to the combination of a number of reasons.
• These are responsible for multiple damages.
• It is difficult to classify the damage and relate
it in quantitative manner due to the dynamic
character of seismic action and inelastic
response of structures.
• The following are the principle cause of the
damage:
10. 1. Soft Storey Failure
• Soft Storey
– The multi storied buildings require open taller first storey for parking
or retail shopping or lobby owing to the lack of horizontal space and
height cost.
– Due to this the first storey has lesser strength and stiffness as
compared to upper stories ,which are stiffened by masonry infill walls.
This creates soft or weak storey problem in multi storey building.
• Problems due to Soft storey:
– Increased flexibility of first storey results in extreme deflections ,
which in turn leads to concentration of forces at the second storey
connections accompanied by large plastic deformation.
– Most of the energy developed during the earthquake is dissipated by
the columns of the first storey, which leads to development of plastic
hinges at the end of columns and lead to collapse of the soft storey.
• The damage has been caused due to the collapse and buckling
of the columns.
11.
12. 2. FLOATING COLUMNS
• The balconies are not counted in FLOOR SPACE
INDEX(FSI), thus buildings have overhanging
balconies in upper stories.
• The perimeter columns of the ground storey are
discontinued in the upper stories and floating
columns are provided along the overhanging
perimeter of the building.( ref fig)
• During an earthquake a clear load path is not
available for transferring the lateral forces to the
foundation .
• Thus the columns begin to deform and buckle
resulting in total collapse.
13.
14.
15. 3. Plan and Mass Irregularities
• Size of building:
– In tall buildings with large height-to-base size ratio, the
horizontal movement of the floors during ground shaking
is large. In short but very long buildings, the damaging
effects during earthquake shaking are many. And, in
buildings with large plan area like warehouses ,the
horizontal seismic forces can be excessive to be carried by
columns and walls.
• Horizontal layout of the Building:
– buildings with simple geometry in plan have performed
well during strong earthquakes. Buildings with re-entrant
corners, like those U, V, H and + shaped in plan have
sustained significant damage
16.
17. 4. Poor Quality of Construction Material
and Corrosion of Reinforcement
• The faulty construction practices and lack of quality
control contribute to the damage of buildings.
• It was observed that the ratio of sand was high.
• The recycled steel was used as reinforcement.
• The corrosion of reinforcement bars occurred due
to:
– insufficient concrete cover
– Poor concrete placement
– Porous concrete
18.
19. 5. Pounding of Buildings
• When two buildings are too close to each
other, they may pound on each other during
strong shaking.
• With increase in building height, this collision
can be a greater problem. When building
heights do not match , the roof of the shorter
building may pound at the mid-height of the
column of the taller one; this can be very
dangerous.
20.
21. DAMAGE TO STRUCTURAL
COMPONENTS
• COLUMNS
– The failure of columns was the most prominent and
widely observed in most of buildings.
– The following reasons are responsible for the column
failure:
• The oblong cross section, a space left at the top of the
column called ‘topi’ is left during casting .
• The relatively slender column sections compared to beams.
• Lack of confinement due to large tie spacing, insufficient
development length, hook configurations of the
reinforcement do not comply with the ductile detailing
practices.
22.
23. – The crushing of the compression zone of the
column is manifested first by spalling of concrete
cover to reinforcement and subsequently the
concrete cover expands and crushes.
– This is followed by buckling of the bars in
compression and by hoop fracture.
– This leads to shortening of the column under axial
load.
– The column not only looses its stiffness but also
the ability to carry vertical loads.
24. • BEAMS
– There have been little evidence of the failure of
the beams .
– But there are many cases of the damage of the
beam-column joints .
– The following reasons are responsible for such
damage:
• The inadequacy of the reinforcement in beam–column
joint .
• Absence of confining hoop reinforcement.
• Inappropriate location of bar splices in columns.
25.
26. • SLAB:
– The cracks are developed in RC slab and beam slab
joints due to ;
• The widening of the existing micro cracks which are
formed either because of the bending action or
temperature/shrinkage.
• These cracks are further widened and visible due to
strong ground motion.
• NOTE: The damage in slab is generally not considered
to be dangerous for the stability of the structure.
27.
28. DAMAGE TO NON STRUCTURAL PANEL
ELEMENTS
• INFILL WALLS
– These are used as interior partition and exterior walls.
– Though their strength and stiffness is ignored in design but
actually infill walls add to strength and rigidity of the
structures.
– During excitation the RC frame is deformed and initially the
first cracks appear on the plaster. As the deformation of frame
increases the cracks penetrate into the masonry and leads to
detachment of the same from the frame.
– Finally the diagonal cracks(X shaped) appear because of strut
action of the infill.
29.
30. • Exterior Walls:
– The un-reinforced masonry walls, when subjected
to intense shaking have tendency to resist large
out of plane vibrations with little sign of distress.
– When the flexural strength of these panels
become insufficient to resist these forces, the
entire infill panel fails.
31.
32. DAMAGE TO WATER TANKS AND PARAPETS
– WATER TANKS:
• Water tanks at the roof level of building experience large
inertia force s due to amplification of the ground
acceleration along the height of building.
• PARAPETS:
–Un-reinforced concrete parapets with height
to thickness ratio and improper anchoring to
roof diaphragm may pose hazard.
–As the height of parapets increases the hazard
posed also increases.
33.
34. DAMAGE TO STAIRCASE
• Staircase and corridors are found to have been
blocked by the failure of the unreinforced
masonry enclosure.
• Stairs can start acting as diagonal bracing
elements during earthquake induced motion and
thus should be used with sliding joints in seismic
design of buildings.
• Isolation of the stairs from the structural system
can also minimize the damage to stairs.
35.
36. DAMAGE TO ELEVATOR
• Elevators are vulnerable to the earthquakes.
• It is important to prevent the damage to
elevator due to the following reasons:
– Danger to passengers trapped .
– These are essential in hospitals which deliver the
health services after an earthquake.
– Undetected damage can cause substantial danger
if elevators are used after the earthquake.
37.
38. EFFECT OF EARTHQUAKE ON CODE
DESIGNED STRUCTURES
• The BIS has published two codes :
– IS 1893(Part1):2002
• It deals with the determination of forces and general
considerations for design of buildings.
IS 13920:1993
It deals with the detailing of reinforced concrete
structures for ductility.
39. • The government buildings follow the design codes as
a mandatory requirement.
• Thus the performance of these buildings in the
earthquake has been relatively better on account of
code compliance.
• The following two government buildings sustained
minor damage in the form of:
– cracking of infill brick wall and non functioning of lift.
Both the buildings were in working condition after the
earthquake and were not required to be vacated.
40.
41. LESSONS LEARNT FROM
DAMAGES OF RC BUILDINGS
• THE DESIGN OF BUILDINGS SHOULD BE BASED ON SEISMIC CODES
IS 1893(PART1):2002 AND IS 13920:1993.
• MULTI STOREY RC BUILDING WITH VERTICAL IRREGULARITIS AS
SOFT STOREY AND BUILDINGS WITH MASS IRREGULARITIES SUCH
AS MASSIVE POOLS ON ROOF TOP AND BUILDINGS WITH FLOATING
COLUMNS SHOULD BE DESIGNED ON BAISI OF DYNAMIC ANALYSIS
AND INELASTIC DESIGN.THE DUCTILITY PROVISIONS ARE
MOSTIMPORTANT IN SUCH DESIGNS.
• MORE CARE SHOULD BE GIVEN AT TIME OF PLANNING.THE
TORSIONAL EFFECT IN BUILDING CAN BE MINIMIZED BY PROPE
LOCATION OF VERTICL RESISTING ELEMEMTS AND MASSS
DISTRIBUTION. BUILDING WITH STRONG-COLUMN AND WEAK
BEAM CAN BE ACHIEVED AT PLANNING STAGE.
• THE SOFT STOREY STIFFNESS CAN BE CONTROLLED BY
APPROPRIATE DESIGN PROCEDURES.
42. • THE INFILL CONSTRUCTION IN RCBUILDINGS SHOULD BE DULY
ACCOUNTED FOR STRUCTURAL ANALYSIS.
• THE STAIRCASE CONNECTION WITH BUILDING SHOULD BE
MADE USING SLIDING JOINTS.
• SHEAR WALL SHOULD BE EMPLOYED FOR INCREASING THE
STIFFNESS AND ARE UNIFORMLY DISTRIBUTED IN BOTH
PRINCIPLE DIRECTIONS.
• EMPHASIS SHOULD BE GIVEN ON THE QUALITY OF
CONSTRUCTION.
