Reasons of failures of RC & Masonry structures

1. Seismic Damages

2. Bhuj Earthquake
• Occurred on 26th January, 2001
• Of magnitude M=6.9 on Richter scale reported by
Indian Meteorological Department
• Located near Bachau (Latitude 23.40 N and
Longitude 70.28 E) focal depth 25km
• Major cities affected are Bhuj, Anjar, Bhachau,
Gandhidham, Kandla Port, Morbi, Ahmedabad,
Rajkot, Sundernagar etc.
• The earthquake killed between 13,805 and 20,023
people (including 18 in southeastern Pakistan),
injured another 167,000 and destroyed nearly
400,000 homes

3. General reasons of failure of RC
structures
• Soft stories
• Floating columns
• Strong column weak beam
• Plan and Mass irregularities
• Poor quality of construction material
• Faulty construction practices
• Pounding of adjacent structures

4. Soft Storey Failure
• A soft storey is one in which the lateral
stiffness is less than 70% of the storey
immediately above, or less than 80% of
the combined stiffness of the three
stories above.
• A typical soft story building of G+4 or
more stories located over a ground level
with large openings, such as a parking
space or series of retail businesses with
large windows.
• The dynamic analysis of these building on
floating columns show these building
vibrate in torsional mode.
• This type of failure results from the
combinations of several other
unfavorable reasons, such as torsion,
excessive mass on upper floors, P-∆
effect and lack of ductility in the bottom
storey.

6. Floating Column
• Usually columns rest on the
foundation to transfer load
from slabs and beams.
• Floating column rest on the
beam, means the beam which
support the column is act as a
foundation. That beam is
called as transfer beam.
• This is widely used in high
storied buildings which is used
for both commercial and
residential purpose. This helps
to alter the plan of the top
floors to our convenience. The
transfer beam that support
floating column will be
designed with more
reinforcement.

7. • Overturning forces thus
developed overwhelm the
columns of the ground
floor.
• Ductile connection at the
exterior beam-column
joint is indispensable for
transferring these forces.

8. Strong column weak beam
• During an earthquake, Columns receive forces from
beams, so columns should be stronger than beams
and foundations should be stronger than columns.
• If columns are made weaker then they suffer
severe damage especially at the joints of lower
storey.
• On the other hand, if the beams are weaker then
damage will first occur in the beams which are
ductile enough and cause progressive damage.
There will be large deformations(ductile failure) in
the building before collapse.

10. Plan Irregularity
• A structural system is considered irregular, when:
• the plans symmetrical axes are noticeably not regular and
perpendicular to each other, when
• there are projections or entrants majors to 15%,
• the vertical resistant elements to the lateral loads are not
parallel, nor symmetrical with respect to main the orthogonal
axes of the system that resists the lateral forces,
• discontinuities in a trajectory of lateral force exist, like
deviations outside the plane of the vertical elements.
• The discontinuities and irregularities in the load transfer
path for transfer of seismic forces, which develops due
to accelerations of individual elements to the ground.

12. Vertical irregularity
• The discontinuous columns, shear
walls, bracing, bracing, forms, that
arise a floating box type situation
• Shear is induced to overturning forces
to another resisting element of lower
level.
• Vertical geometric irregularity is
considered when the horizontal
dimension of the lateral load force
resisting system in any storey is more
than 150% of that in adjacent storey.
• The solution of this problem is the
total separation of the building
corners.

13. Horizontal Irregularity
• Unsymmetrical plan shapes
• Plan irregularities like L,T,U,F,C etc. shapes lead in larger
torsional forces
• Re-entrant corners
• The inside corners of an asymmetrical buildings in plan are
subjected to stress concentration and are prone to damage

14. • Non-parallel system
• In triangular and trapezoidal shapes, the columns and shearwalls are not
parallel resulting in high torsional foces.
• Diaphragm discontinuity
• A plan system is considered irregular, when the diaphragms present
discontinuities or variations of rigidity, including the caused ones by
areas trimmed or with opens majors of 20% of the gross area locked up
of the diaphragm or changes in the effective rigidity of the diaphragm of
50% of a following floor.

15. Mass irregularity
• Mass irregularity is considered
to exist when the effective mass
of a storey is more than 200% of
the effective mass an adjacent
storey.
• The effective mass of the storey
is the dead weight of the floor
plus partition walls
• The increased mass result in
increased inertia forces and
may result in heavy damage.

16. Torsion Irregularity
• Torsion irregularity exists when the
maximum relative displacement of the
floor calculated including the accidental
torsion, in the end of the structural cross-
section to an axis is more than 1.10 times
the average of the relative displacements
of the floor of both extreme of the
structure.
• The torsion also is induced with the
positioning of rigid elements of
asymmetric way, with the positioning of
great masses or the combination of both.

17. Poor quality of Construction
material and corrosion of
reinforcement
• Inferior quality of steel or water used result in
corrosion of reinforcement which result in spalling
of concrete
• The corrosion of reinforcement is also caused by
insufficient cover, porous concrete and less
compaction.
• Faulty construction practices include:
• Improper proportioning of concrete ingredients
• Low cement-sand ratio
• Wrong placement of steel bars
• Inadequate development length
• Improper splicing

18. Pounding of Building
• Pounding effect is caused
due to the hammering of
adjacent building of
different heights.
• Buildings of different
height hit against each
other damaging the
columns due to hammering
of floors
• Damage due to pounding
may be minimized by
providing proper
separation or by aligning
floors of adjacent
buildings.

19. Inadequate ductile detailing of
structural elements
• Improper spacing of lateral ties in columns
lead to shear failure.
• If the ends of the ties are not hooked properly
then they may open up during earthquake
motion.
• Incorrect splicing of column bars.

21. Damage to the infill walls

22. Damage to the water tanks and
parapet
• Water tanks are generally constructed at the
roofs of the structures.
• These tanks experience large inertia forces
due to heavy weight and height of the
building.
• Unreinforced concrete parapets which are not
properly tied to the root are also damaged
during the earthquake.

24. Damage to
staircase

26. Lessons learnt from damages of
RC Building
• The design of building should based on seismic
codes IS 1893(Part I): 2002 and IS 13920: 1993
• The RC building with irregularities like soft storey,
mass irregularities, floating columns should be
designed on the basis of dynamic analysis and
inelastic design. The ductility provisions are most
important in such situations
• The torsional effects in a building can be
minimized by proper location of vertical resisting
elements and mass distribution
• Building design with strong column weak beam can
be achieved at the planning stage.

27. • The infill construction should be duly
accounted for in structural analysis.
• The staircase connection with building should
be made using sliding joints.
• Shear walls should be employed for increasing
stiffness and are uniformly distributed in both
principal directions
• There should be a greater emphasis on the
quality of construction

28. Seismic damages to Masonry
Structures
• Out of plane failure
• In plane failure
• Connection failure
• Diaphragm failure
• Failure due to openings in the walls
• Pounding
• Non-structural component failure

29. Out of plane
failure

30. In plane failure

31. Connection failure

32. Diaphragm failure

33. Failure due to
openings in walls