1. PRAKASH PAUDEL GRAPHIC ERA UNIVERSITY FIRST SEMESTER
SEMINAR
2. Performance of Non-Engineered masonry Buildings During
Earthquakes Stone masonry buildings tend to perform poorly in
earthquakes owing to the low strength of the stone and mortar used
and the lack of adequate wall connections The failure pattern of
such masonry structures during earthquake can be classified as
3. Out-of-plane flexure failure shear failure
4. Separation of wall at junctions Failure of masonry piers
between openings
5. Local failures Separation of roof from walls
6. Collapse of wythes`
7. Simplicity and symmetry in plan and elevation Building
Height In general, stone masonry buildings should not be taller
than 2 storeys when built in cement mortar, and 1 storey when built
in lime or mud mortar Roofs Lighter roofs are preferable to heavy
roofs. Sheeted roofs are better than tiled roofs All elements of a
roof should be so integrated that it may have the capability of
acting as one stiff unit in plan for holding the walls together
EARTHQUAKE PROTECTION MESURES:- Architectural Design
Features:-
8. Floors For holding the walls together, the floor elements
should have full bearing on the walls Opening in Walls For better
seismic behavior openings should be as small and centrally located
as functionally feasible Enclosed space Within a building, smaller
rooms with bonded long and short walls forming a crate like
enclosure, are seismically stronger than rooms with long
uninterrupted masonry walls
9. Fall of roof because of Inadequate connection between roof
and wall 1- Earthquake 2- Flat joisted roof 3- Fractional support,
no connection 4- Out of phase motion 5- Crack 1 1 2 3 5 1 4
10. Quality of Construction and Maintenance Good quality of
building materials - mortar and building units of good strength
Proper bond so as to break vertical joints in walls Construction of
walls truly vertical Proper continuity at corners and wall
junctions
11. The masonry walls should be built in construction lifts not
exceeding 600mm. Through- stones (each extending over full
thickness of wall) or a pair of overlapping bond-stones (each
extending over at least ths thickness of wall) must be used at
every 600mm along the height and at a maximum spacing of 1.2m along
the length (Figure 3).
12. Ensure proper wall construction The wall thickness should
not exceed 450mm. Round stone boulders should not be used in the
Construction Instead, the stones should be shaped using chisels and
hammer Control on overall dimensions and heights The unsupported
length of walls between cross walls should be limited to 5/6m for
longer walls, cross supports raised from the ground level called
buttresses should be provided at spacing not more than 4m. The
height of each storey should not exceed 3.0m
13. Horizontal Bands Why are Horizontal Bands necessary in
Masonry Building providing out-of-plane bending resistance to the
wall by forming a rigid horizontal frame with continuity at the
corners reducing the unsupported vertical height of the wall to
that between the two consecutive bands, like plinth and lintel
14. There are four types of bands in a typical masonry
building, namely gable band, roof band, lintel band and plinth band
, named after their location in the building The lintel band is the
most important of all and needs to be provided in almost all
buildings The gable band is employed only in buildings with pitched
or sloped roofs
15. Fig:-Working principle of horizontal bands
16. Building with no horizontal lintel band: collapse of roof
and walls A building with horizontal lintel band in Killari
village: no damage
17. Vertical bands Why is Vertical Reinforcement required in
Masonry Buildings?
18. Types of damage in buildings without vertical bands Rocking
of masonry piers When the ground shakes, the inertia force causes
the small- sized masonry wall piers to disconnect from the masonry
above and below. These masonry sub-units rock back and forth,
developing contact only at the opposite diagonals The rocking of a
masonry pier can crush the masonry at the corners
19. X-Cracking of Masonry Piers The rocking of a masonry pier
can crush the masonry at the corners. Rocking is possible when
masonry piers are slender, and when weight of the structure above
is small. Otherwise, the piers are more likely to develop diagonal
(X- type)shear cracking (Figure 2c); this is the most common
failure type in masonry buildings.
20. Horizontal sliding at sill level in masonry building During
strong earthquake shaking , the building may slide just under the
roof, below the lintel band or at the sill level. Sometimes, the
building may also slide at the plinth level. The exact location of
sliding depends on numerous factors including building weight, the
earthquake -induced inertia force, the area of openings, and type
of doorframes used.
21. When a wall with an opening deforms during earthquake
shaking , the shape of the opening distorts and becomes more like a
rhombus - two opposite corners move away and the other two come
closer. Under this type of deformation, the corners that come
closer develop cracks . The cracks are bigger when the opening
sizes are larger Cracking in building with no corner
reinforcement
22. How Vertical Reinforcement Helps ? Embedding vertical
reinforcement bars in the edges of the wall piers and anchoring
them in the foundation at the bottom and in the roof band at the
top , forces the slender masonry piers to undergo bending instead
of rocking Steel bars provided in the wall masonry all around the
openings restrict these cracks at the corners
23. Sliding failure mentioned above is rare, even in unconfined
masonry buildings. However, the most common damage, observed after
an earthquake, is diagonal X- cracking of wall piers, and also
inclined cracks at the corners of door and window openings
24. Fig 6: Containment reinforcement scheme integrated with
horizontal bed reinforcement Fig 7: Schematic diagram of vertical
and horizontal reinforcement in a masonry building Specification
for vertical containment reinforcement
25. Normally, the horizontal spacing between two sets of
containment reinforcement should be between 0.75m to 1.25m. The
wires/rods of containment reinforcement must be tied to the steel
in the horizontal band to form a coarse two-dimensional cage
holding the masonry in place. For providing vertical bar in stone
masonry a casing pipe is recommended around which the masonry is
built to heights of 600 mm, The pipe is kept loose by rotating it
during masonry construction. Then the casing pipe is raised and the
cavity below is filled with 1:2:4 concrete mix and rodded to
compact it. The concrete will not only provide the bond between the
bar and the masonry but will also protect the bar from
corrosion.
