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Chapter-09
Masonry Structures underlater loads
Siddharth shankar
Department of Civil(structure)
EngineeringPulchowk Campus
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Earthquake
Earthquake cause shaking of ground, so a building resting onit will experience motion at its base.
The roof has a tendency to stay in its original position and the
roof experiences a force, called inertia force.
Inertia force is the multiplication of the weight and theacceleration, so larger the weight of the building more the
earthquake shaking.
F
Engineering representation of
earthquake force
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Masonry Structures
Masonry is brittle and tensile and shear strength
is very low.
Due to Large mass of masonry structures,
heavy weight attracts large amounts of seismicforces.
Wall to wall connection and roof connection is
generally weak.
Stress concentration occurs at the corners of
windows and doors.
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Out of plane failure
In plane failure
Diaphragm failure Connection Failure
Failure due to opening of wall
Pounding
Non-structural component failure
Failure Modes of a Masonry buildings
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Out of Plane Failure
The Earthquake force isperpendicular to the plane.
The wall tends to overturn or bend.
This causes the partial or full
collapse of the wall.This is due to Inadequate anchorage
of wall and roof , long and slender
wall, etc.
Characterized by vertical cracks atcorner, cracks at lintel, roof level and
gable wall, etc.
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In Plane Failure
The Earthquake force is parallel to the plane
The wall is shear off or bendX- cracks occurs
Characterized by vertical cracks at wall intersection,
separation of corners of two walls, spalling of
materials, etc
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Diaphragm Failure
Lack of anchoring produce a push of diaphragm against thewall.
Absence of good shear transfer between diaphragms and
reaction wall accounts for damage at corner of wall
Rare phenomenon in the event of seismic motion
Separation of wall and diaphragm cause collapse of buildings
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Connection failure
For given direction of earthquake, wall A acts as a shearwall and B acts as flexure wall.
If the walls are not tied together wall B overturn (out of
olane) and wall A slides (in plane) and collapse occurs.
Masonry units should tied properly
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Failure due to opening in walls
Opening will obstruct the flow of forces from one wall toanother.
Large opening in shear wall reduces the strength of wall
against the inertia forces.
Results diagonal cracks in the areas of masonry betweenopening and cracks at the level of opening.
Thus, openings should small and away from corners.
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Pounding
When the roofs of two adjacent buildings are at differentlevels, during earthquake, two buildings strike against each
other is called pounding.
Pounding results into cracking of the wall.
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Non Structural components failure
Falling of plaster from walls and ceiling.
Cracking and overturning of parapets,
chimneys, etc.
Cracking and overturning of partition walls.
Cracking of glasses.
Falling of loosely placed objects.
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Ductile behaviour of reinforced & unreinforced masonry
It is the capacity of an element or structure to undergo largedeformation without failure.
Masonry is brittle in nature.
Ductility of masonry structure is governed by the ductility
of masonry units & properties of mortar.Unreinforced masonry cannot withstand tension so cracks
develops.
In-plane & out-of-plane failure is also due to ductility of
masonry.
To improve ductility reinforcing bars are embedded in the
masonry, called reinforced masonry which can resist the
seismic force more than unreinforced masonry.
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Brittle and Ductile force-deformation behavior
Brittle
Ductile
Force
y uDeformation
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1. Walls tend to tear apart.
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2. Walls tend to shear off diagonally in direction.
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3. Failure at corners of walls
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4. Walls tend to collapse
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5. Failure at corners of openings
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6. Hammering/pounding between two adjacent
buildings
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7. Separation of thick wall into two layers
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8.Separation on unconnected wall at junction
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9.Seperation of wall from roof
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Non-integrity of wall floor and roof.
Configuration irregularity of building causes
torsional effect.
Large opening of the building. Inappropriate position of opening.
Lack of cross wall in large length of wall.
Lack of reinforcement make the masonry buildingbrittle.
Pounding effect.
Lack of anchoring element between two walls.
Major causes of failure of masonry buildings
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Elements of Lateral Load
Resisting MasonrySystem
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Horizontal bands for integrity
Connecting peripheral walls forstructural robustness and integrity
Plinth band
Lintel band
Roof band
Gable band
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Roof structure
Light and strong roof is
desirable.
Secure tiles/slates or use GI
sheets.
Good jointing in trusses
Concrete floors in 1:2:4
concrete with reinforcement
in both directions and bend
up near supports.
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Overall arrangement of masonry structure
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Chapter-10
Testing of masonry
elements
siddharth shankar
Pulchowk CampusDepartment of Civil Engineering
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Compressive Strength of Bricks and wall
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Testing of Wall in compression
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Diagonal Shear Test
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Normally carried out:
1. Periodically to evaluate the performance ofbuilding
2.To gather information on old building in
order to ascertain the methods of repair or
to demolish
3. To ascertain the strength of concrete if
cube tests failed.
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NON DESTRUCTIVE TEST (NDT)
Elastic wave tomography
Rebound Hammer / Schmidt Hammer
Ultrasonic Pulse Velocity
Impact Echo Test
X-Rays
Flat Jack Test
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Elastic wave tomography Technique used for locating shallow delaminations,
cracks, and voids.
Elastic wave tomography is based on two basicprinciples from heat transfer: conduction and
radiation. Sound materials with no voids, gaps, orcracks are more thermally conductive than materialsthat are delaminated or contain moisture.
This allows rapid areal mapping of internal
conditions. It should be noted that the IT method ismost useful for the detection of shallow defects andflaws.
Tests For:Voids, Cracks, Moisture.
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Rebound Method Can be used to determine the in-place compressive
strength of concrete within a range of 1500 8000 psi
(10-55MPa)
A quick and simple mean of checking concrete
uniformity.
Measure the distance of rebound of a spring-loaded
plunger after it struck a smooth concrete surface.
Results of the test can be affected by factors such assmoothness of concrete surface, size, shape, rigidity of
specimen, age & moisture condition.
Type of coarse aggregate & the carbonation of the
surface.
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Nondestructive Test
Re-bound hammer Method
http://www.worldoftest.com/images/ndt/WM250.jpg -
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Nondestructive Test Methods
Rebound Hammer Tests Schmidt Hammer
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Rebound Method Using Rebound Hammer
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Ultrasonic Pulse Velocity
It uses measurement of the speed of ultrasonic
pulses through the concrete to correlate concrete
strength to standard strength.
Allows the determination of compressive concrete
strength and location of cracks.
It will identify non homogenous condition in the
structure such as honeycomb, voids and cracks.
Size of cracks can also be determined.
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Ultrasonic Pulse Velocity
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Flat Jack Test Flat jack testing is a nondestructive test of
evaluating existing masonry structure. It does
not require removal of masonry units - only
the removal of small portions of mortar isenough. The flat jack test uses small, thin,
hydraulic jacks to apply a force to a section of
an existing masonry wall, and the methoduses measuring devices to determine the
resulting displacement of the masonry.
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Flat jack testing has many useful applications:
It can be used to determine masonry compressivemodulus, which is the stress/strain relationship
of the masonry, or axial stress by applying axial
load and measuring resulting axial deformation. It can be used to estimate compressive strength
and measure the shear strength.
If the destruction of the masonry units isacceptable, it can be used to directly measure the
compressive strength by testing the masonry to
failure.
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Flat-Jack Test
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Push Shear Test
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Prepare the test location by removing the brick,
including the mortar, on one side of the brick to be
tested. The head joint on the opposite side of the
brick to be tested is also removed. Care must be
exercised so that the mortar joint above or below thebrick to be tested is not damaged.
The hydraulic ram is inserted in the space where the
brick was removed. A steel loading block is placed
between the ram and the brick to be tested so that theram will distribute its load over the end face of the
brick. The dial gauge can also be inserted in the
space.
Push Shear Test
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The brick is then loaded with the ram until the
first indication of cracking or movement of
the brick.
The ram force and associated deflection on
the dial gauge are recorded to develop a force-
deflection plot on which the first cracking or
movement should be indicated. A dial gaugecan be used to calculate a rough estimate of
shear stiffness
Push Shear Test
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