confined masonry training pakistan

8/9/2019 Confined Masonry Training Pakistan

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Confined masonry

Confined masonrySDC

Lesson prepared by the Swiss Agency for Development and Cooperation for thetrainings at the Housing Reconstruction Centres Ballakot and Battagram

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Confined masonry

DefinitionConfined Masonry is a construction system

where the walls are built first, and the

columns and beams are poured inafterwards to enclose (confine) the wall.


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Confined masonry

Concept

The walls are tieddown to the foundation.

The ties work like a string around a parcel.

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Confined masonry

Difference with RC frames

Confined Masonry

Walls first

Concrete later

Reinforced Concrete Frame

Concrete first

Walls later


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Confined masonry


Confined Masonry

Walls ensure rigidity


Column beam connectionsensure rigidity

Straightforwardtransmission of efforts

Complicatedtransmission of efforts

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Confined masonry


Confined Masonry

Walls are anchored to theframes through indentation.

(Additional re-bars willimprove anchoring)


Walls are usually notanchored to the frames and

will fall out.

Later anchoring of walls canbe difficult


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Confined masonry


Confined Masonry Reinforced Concrete Frame

All efforts go through thebeam-column connection.

If they are badly done,they break.

Concrete goes intothe indentation of

the brick wall

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Confined masonry

Summing up

Confined Masonry

Its the walls that do the work.

Thats why they are calledload bearing walls.


Its the columns and beams that

do the work.

Walls are only infills.

From here on well talk about

load bearing walls made withthe confined masonry system.


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Confined masonry

(the walls shown here are not confined)

Walls

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Confined masonry

Walls: why do we need them

A building needs walls for

1. Protection against climate, view, intruders, etc.

+When we talk about load bearing walls, they will

2. Carry the roof and/or upper floor (vertical loads)

+

When we talk about earthquakes, they will also3. Carry the lateral pushes (horizontal loads)


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Confined masonry

Load bearing walls

They can be made out of:

Bricks Stone

Cement blocks

Most importantly, they must be strong. Water the bricks or blocks before use

Fill all joints (horizontal and vertical with mortar) Use the right mixture for the mortar (1 bucket of

cement for 5 buckets of clean and rough sand)

+ cement or cement/lime mortar

+ reinforced concrete confinements

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Confined masonry

Load bearing walls

All load bearing walls must be confined.

or

All confined walls are load bearing.


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Confined masonry

Earthquake resistance

When we talk earthquake resistance, we areparticularly interested in the capacity of a wall towithstand horizontal loads.

Confined walls work also for horizontal loads.

Horizontal load

Horizontal load

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Confined masonry

Horizontal loads

In an earthquake the groundmoves sideward. Thats likepushing the roof. The walls musthelp to resist this horizontal load.

A serious earthquake (0.35 g) hasthe same effect on a house astilting it at an angle of 20.5degrees. Thats why walls mustbe strong.

20.5


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Confined masonry

Distribution of wallsThe earthquake resistance of ahouse is much better, if least two

strong walls without openings(called shear walls) are placed ineach direction.

These shear wallsmust beplaced as far away from each

other as possible.

Special casewith walls inthe centre

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Confined masonry

Distribution of walls

The shear wallsmust be placed

symmetrically and as far awayfrom each other as possible toavoid rotation.


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Confined masonry

Shear walls

Shear walls cannot have any openings and no slits forpipes!

Shear walls should ideally be as long as they are high.

Minimum length should be 2/3 of their height.

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Confined masonry

Shear walls

Shear walls should not be higher than 8 feet.

If the wall is higher, an intermediate bond beam must beintroduced at 8 feet.


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Confined masonry

Shear walls

The total surface on the ground of

all shear walls (L x B) in the samedirection must be between 1.0%and 1.4% of the roof surface (with2 floors, add up each floor),according to the soil.

Example:

If you roof surface is 400 sqft, thetotal shear wall surface touchingthe ground must be 4 to 5.6 sqft(i.e. all shear walls added up)

1.4%Loose sandsoft clay

Soft of loose

1.2%Hard clayishsand

Intermediate

1.0%RockGravel

Hard

Min. wallsurface onground

DescriptionType of soil

Blondet 2005

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Confined masonry

Shear wallsExample: Total surface of shear walls on the ground =

1.0 to 1.4% of roof surface in this direction.

The same calculation must be repeated for the otherdirection.

Blondet 2005


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Confined masonry

Construction details

Foundation

Plinth beam

Walls

Columns

Bond beam

Roof slab

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Confined masonry

Construction details

Step by step 1. Column reinforcements

2. Foundations

3. Plinth beam4. Walls

5. Doors and windows

6. Bond beam

7. Roof slab8. Extensions


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Confined masonry

Column reinforcements

General rules

1

3

Alternateposition of hooks

Bend hooks at45 degrees

All rebars must becovered by at least1 inch of concrete

Always use steel barswith ridges (smoothrebars may only beused for stirrups)

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Confined masonry

ColumnreinforcementsPrepare columns

reinforcements:

Through plinth and bondbeams place stirrups at 4intervals.

Keep this interval for 2

feet in the lower and upperpart of the column.


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Confined masonry

Plinth beam

Prepare the reinforcement of the plinth beam

Dont forget:stirrup ends bentat 45 degrees!

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Confined masonry

1 1

1

1 Distance blocks(height 1 )

Plinth beamPlace plinth beam reinforcementon foundation using distanceblocks or spacers.

The distance blocks must also beput on both sides to keep thedistance to the formwork.


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Confined masonry

Plinth beamConnect beams to columns usingstraight rebars and pins

Overlapping 50 cm

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Confined masonry

Brick wallsUse only bricks with frogs orvertical holes

Water the bricks before use


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Confined masonry

Brick wallsUse the Flamish rather than the English bond. It has an equalnumber of joints in each layer, thus ensures more regular mortar

joints (i.e. all of the same thickness).

Flamish Bond English Bond

6 joints

3 joints

6 joints

3 joints

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Confined masonry

Brick wallsEnd walls in zig-zag towardscolumns

Avoid continuous joints


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Confined masonry

Brick wallsAll joints (horizontal and vertical)must be between 3/8 and .

Join walls carefully by alternatingbrick connection.

1st layer

2nd layer

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Confined masonry

Brick wallsDont build higher than 4 feet perday!

Protect fresh walls in hot climatesagainst drying out.


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Confined masonry

Improved wall anchoringTo improve connection betweencolumns and walls, use stitches

made of rebar anchors ( 1/3 or8mm).

Place anchors every 1 foot.

Place the anchor bars in a bed ofconcrete the height of a brick layer.

Anchors must end with a hook.

Link anchors with small stirrups.Stitches

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Confined masonry

Improved wall anchoring Add horizontal through bands at sill and lintel level, even if youdont have a window. These bands will secure the wall against beingknocked out during an earthquake.

Seismic bandat lintel level

Seismic bandat sill level

Seismic bandrebars 3/8,

h = brick course

Stitches


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Confined masonry

Bond beam

Prepare the reinforcement of the bond beam

Dont forget:stirrup ends bentat 45 degrees!

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Confined masonry

Bond beam

Connect bond beams to columns with straight rebars andpins.


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Confined masonry

Roof slab

For spans up to 11 feet

@ 10

3/8 @ 8 3/8 @ 8

6

2

Distanceblocks 1

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Confined masonry

Roof slab

Example of reinforcement bar distribution for a span of 11 feet.


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Confined masonry

Roof slab

A roof pulled over the wall

edge is another good method(protects the walls againstrain).

But you still have to place abond beam over the walls asshown on the previouspicture.

Make sure that the slabrebars go correctly throughthe bond beam.

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Confined masonry

Roof slab

Water the slab and keep it wet for one week.


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Confined masonry

Column roof slab connection

If you want the column rebarsto stick out of your roof for

future extensions, they mustbe:

Long enough (at least 2feet).

Cast in concrete (toensure correctanchoring).

Otherwise its better to bendthem into the bond beambefore casting the slab!

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Confined masonry

Roof terrace

If you want to make a roof terrace, theterrace walls must be anchored like allother walls.


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Confined masonry

Roof terrace

Avoid putting your terrace wall on acantilevered cornice, as it will fall onyour head during an earthquake.

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Confined masonry

Slope roof

You can use the column reinforcement bars sticking out of the roofslab to anchor the beams of a slope roof.


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Confined masonry

Retaining walls

If you build against aslope, you must makeretaining walls at least2.5 feet away from thebuilding.

Retaining walls keepaway the pressure of theslope and of the water.

If you make retainingwalls in dry stonemasonry or situ theymust have an inclinationof 1 to 5.

The walls of your house must not be in direct contact with the ground!

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Confined masonry

Retaining walls

To lead away rain water(including all water thathas rained on the slopeabove your house), makea drainage canal aroundthe house.


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Confined masonry

Gaps between buildingsTo avoid damage among twobuildings, or an extension to the

original building, a gap of 1/100thof the height is compulsory.

This gap must be absolutelyempty and clean (no mortarrests).

Example: Height of the building

12 feet (3.6m), the gap must be1 (36mm).

Take into account any futuresecond floor!

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Confined masonry

They will brake away during anearthquake, thats all.

Gaps between buildingsClose gaps with bricks placed infront of them.


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Confined masonry

Find the error

No distance blocks

or spacers in theroof slab.

These rebarsexposed on thesurface will rustquickly andbecome

ineffective.

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Confined masonry

Find the error

Stirrups are notbent at a 45

degree angle.


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Confined masonry

Find the error

The overlapping

length isinsufficient

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Confined masonry

Find the error

Bond beam mustbe cast together

with the roof slab.


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Confined masonry

Find the error

Bond beam must

be cast togetherwith the roof slab.

Depending on thedirection (i.e. in thedirection of theshorter span), thehorizontal

reinforcement barsmust end in ahook.

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Confined masonry

Find the error

Slab is castagainst another

house. There is nomovement joint toprotect your houseagainst thehammering of yourneighbours houseduring a quake.


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Confined masonry

Find the error

These distance blocks orspacers dont have a wire toattach them to the rebars. Theycan move while pouring theconcrete.

You should prepare them asshown below, each block with awire:

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Confined masonry

Find the error

Concrete has not been vibratedcorrectly to fill every gap.

You should use a vibrator when

casting concrete, or at leasthammer against formwork tomake sure that the concrete fillsevery hole.

Dont add more water to theconcrete to make it more fluent.It will become weaker.


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Confined masonry

Find the error

Wall is to highwithoutintermediateseismic band.

An opportunityhas been missed:for little moremoney a muchstronger wallcould have been

made.

SDC

Confined masonry

Further reading Blondet M. (2005), Construction and Maintenance of Masonry Houses, Pontifica

Universidad Catolica del Peru, Lima,www.eeri.org/lfe/clearinghouse/kashmir/resources.html

City (year n/a), Confined Masonry Construction, City University London,

www.staff.city.ac.uk/earthquakes/MasonryBrick/ConfinedBrickMasonryP.htm Earthquake Hazard Centre, Newsletter, Victoria University of Wellington, New

Zealand, www.vuw.ac.nz/architecture/research/ehc/

AIS 2001), Manual de construccion, evaluacion y rehabilitacion sismoresistente en viviendas e mamposteria, Asociation Colombiana de IngenieriaSismica, www.desenredando.org/public/libros/2001/cersrvm/index.html

NICEE (2004), Guidelines for Earthquake Resistant Non-EngineeredConstruction, Chapter IV: Buildings in Fired-Brick and other Masonry Units,National Information Centre of Earthquake Engineering, IIT Kanput,www.iitk.ac.in/nicee/iaee_english/Chapter4.pdf

IITK-BMTPC, Earthquake tips 1-24, Indian Institute of Technology Kanpur (IITK) andB ildi M t i l d T h l P ti C il (BMTPC)

confined masonry training pakistan

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