Masonry Structures - Under Lateral Loads

5/28/2018 Masonry Structures - Under Lateral Loads

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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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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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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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Masonry Structures - Under Lateral Loads

Documents

lateral loads

wall connection

shear wall

etc5282018 masonry structures

wall b

wall intersection

planethe wall

flexure wall