Structure Repairs & Rehabilitation

Report
Structure Repairs &
Rehabilitation In Low Strength
Masonry Buildings
Presentation From TSG
Structure Repairs & Rehabilitation
Low Strength Masonry Building is Laid in
• Fired brick work in clay & mud mortar
• Random rubble ; Uncoursed, Undressed stone
masonry in weak mortars made of cementsand , lime-sand & clay-mud.
Structure Repairs & Rehabilitation
Component Of Low Strength Masonry Building:
• Foundation
• Flooring
• Brick/ Stone Columns
• Brick Work
• Stone Masonry
• Wood Work
• Slab
• Slopping Wooden frame Roof
• Plaster
Structure Repairs & Rehabilitation
Life Of Structure Depend Upon:
A. Geography Of Location
B. Building Material
C. Technology
D. Workmanship
Structure Repairs & Rehabilitation
A . Geography Of Location:
• Type of Strata
• Water Table
• Earth Quack, Wind, Cyclone, Flood, Snow
• Pollutant
• Land Slide
• Tree location w.r.t. building
Structure Repairs & Rehabilitation
B . Building Materials
• Cement
• Lime
• Fine Sand
• Coarse Sand
• Coarse Aggregate
• Quality of Water
• Bamboo/Wood
• Brick
Structure Repairs & Rehabilitation
C. Technology
• Architectural Design
• Structural Design Based On Load Bearing Wall
• Construction Methods
• Quality Practices
• Construction Management
Structure Repairs & Rehabilitation
D
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Workmanship
Structural Work
Finishing Work
Water Proofing Work
Development of Drainage (Internal &
External)
• Maintenance Of Building
Structure Repairs & Rehabilitation
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Building Needs Repairs & Retrofitting
Crack & Spalling In Structural Members
Crack & Settlement In Flooring
Crack & Spalling in Non Structural Members
Leakage In Water Supply & Drainage System
Redesigning existing structure for nature
forces
Changed functional requirements
Structure Repairs & Rehabilitation
Crack & Spalling In Structural Members
• Cracks Occur Due To Settlement In Foundation
• Cracks Due To Earth Quack ,Wind
• Crack Due To Overloading Of Structure
• Crack Due To Reduction in Load Carrying
Capacity of Structure Due To Weathering
• Crack Due To Improper Design Of Structure
• Crack due to Poor connection Of Structural
Members Resulted From Poor Workmanship
Structure Repairs & Rehabilitation
Crack & Settlement In Flooring
• Due To Improper Plinth Filling
• In case of black cotton soil in foundation not
replaced up to sufficient depth by Good Soil under
plinth (For generating enough Counter weight upon
black cotton soil)
• Water Table vary within the Plinth Sub base (this
occur in frequent flooding area & near sea soar)
• Improper curing, Improper laying, Poor Quality of
workmanship.
• Improper design for loading i.e. thickness & type of
flooring.
Structure Repairs & Rehabilitation
Crack & Spalling in Non Structural Members
• Crack In Plaster
• Crack In Finishing
• Crack In Water Proofing Work
• Vertical cracks in long boundary wall due to
thermal movement Or Shrinkage.
• Crack Induced due to thermal changes,
change in moisture content in building
material, Chemical Reactions
Structure Repairs & Rehabilitation
Leakage In Water Supply & Drainage
• It may result from structural cracks & settlement
• Improper selection of pipe thickness
• Improper selection of Supports & its spacing to
Pipe
• Improper making Of joints
• Non Provision for contraction & expansion
(Particularly when pipe is passing over different
type of long structures)
• Non Testing of Pipe before & after laying
• Insufficient soil cover over pipe
Structure Repairs & Rehabilitation
Redesigning existing structure to meet functional
requirement as well as forces generated by Nature
It is a comprehensive task & require planning which
include following Information gathering.
• Field investigations including details of sub strata,
foundation details
• Type of Existing structure & its members stability
• Design Data Collection
• Identification of components required to be
strengthened, replaced.
• Cost Estimates (it is feasible up to 60% of new
construction)
• Method or Procedure to be fallowed.
Structure Repairs & Rehabilitation
Crack Investigation
• Location
• Profile (vertical, Horizontal, Diagonal)
• Crack Size throughout length (Width,Depth & length)
Thin crack< 1mm
Medium Crack >1 to 2 mm
Wide Crack > 2 mm
Crack may be non-uniform width. i.e. Tapper in
width(narrow at one end & wider at other end. )
• Static or Live cracks
Structure Repairs & Rehabilitation
• Cracks are static or live, is monitored & recorded
by “Tell-Tale” method
Widening Of Crack
Crack
in wall
Quick setting
mortar or
Adhesive
Marking
Crack in
in Glass
Glass strips
Glass strips of 2 to 3
C.M. in width & 10 to
12 C.M.in length
Structure Repairs & Rehabilitation
These Crack occur
around opening due
to drying shrinkage &
thermal movement in
a building resulting
weakening in the wall.
Structure Repairs & Rehabilitation
Expansion & thickening of
roots creating
concentration of stress at
joints & weak locations such
as openings
Structure Repairs & Rehabilitation
The long horizontal crack resulted due to
deflection of slab and lifting up of edge of the slab,
combined with horizontal movement in the slab
due to shrinkage.
Structure Repairs & Rehabilitation
This Cracks are due to pull exerted on the wall by the slab because of
drying shrinkage and thermal contraction this pull results in bending of
the wall which causes cracking at a weak section, that is, at the lintel or
sill level of the window openings. Such cracks generally occurs when
windows and room spans are very large. This cracks can be avoided by
providing slip joints at slab supports on the walls.
Structure Repairs & Rehabilitation
Construction Details Of Bearing Of R.C.C. Roof Slab
Over a Masonry Wall
12 mm Gap
,3/4 filled
with Mastic
Compound
Concrete Fillet
Brick tiles or Cement mortar
with chequer grove finish
First Course Of
parapet masonry is
thicker than the wall
By half Brick
12 mm wide groove in plaster
Slip Joint(two or three layer of
tarred paper are placed over
plastered surface)
Structure Repairs & Rehabilitation
Thickness of plaster is
to much high & silt
content is also Very
High
Structure Repairs & Rehabilitation
Longer opening &
less bearing &
deteriorated lintel
load capacity
exposes diagonal
crack which is
widened towards
corner wall edge.
Structure Repairs & Rehabilitation
Vertical crack under
window occur when
wall have large window
opening & little wall
space on both side of
opening. Difference in
stress due to more
stress in wall portion
adjoining to window &
less stressed portion
under sill of window
results in crack.
Structure Repairs & Rehabilitation
Cantilever Chajja
not having main
bars on upper face
Structure Repairs & Rehabilitation
When two adjacent walls shake in different
directions, their joint at corners comes under a lot of
stress. This causes crack at the junction of two walls.
In Normal conditions, cracks
in this location comes when
one of wall expand more
than short wall.
Structure Repairs & Rehabilitation
When the long wall bends outward or inwards
vertically in the middle of its length, this stretching
causes tension and causes vertical cracks in the
walls.
Structure Repairs & Rehabilitation
Similarly when the walls bends outward or inwards
horizontally in the middle of its height, this stretching causes
tension and causes horizontal cracks in the walls. This happens
at the base of gable wall.
Structure Repairs & Rehabilitation
Many times the wall gets pulled from its corners. This results in
to tearing of wall in diagonal direction. In the wall if there is a
window or a door, then the diagonal crack occur at their
corners.
Structure Repairs & Rehabilitation
Flexural Tension Cracks At Lintel Level Due to Shrinkage &
contraction of R.C.C. Slab
Structure Repairs & Rehabilitation
If the window is very large or if there are many
doors and windows in a wall, then it tears even
more easily in an earthquake.
Structure Repairs & Rehabilitation
Many times the roof slides on top
of the walls on which it is sitting on
Structure Repairs & Rehabilitation
Structural Repairs
Load Bearing Walls: PROCEDURE IN NEXT SLIDE
CRACK IN BRICK
PLACING OF RCC
BLOCK AFTER
CUTTING HOLE IN
B.W.
Structure Repairs & Rehabilitation
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•
•
•
Repairing Of Crack Due To Structural Cause
Replace all cracked bricks
Use R.C.C. Stitching Block In Vertical Spacing In
Every 5th or 6th Course ( 0.5 meter apart ).
Stitching block
Width=equal to wall width,
Length = 1.5 to 2 bricks,
Thick =1 or 2 bricks as per severity of cracks
Mortar For Repairs 1:1:6 (1 Cement :1 lime: 6
sand)
Structure Repairs & Rehabilitation
load bearing walls(May be Brick or Stone) have
inbuilt deficiency.
• Each Brick have different strength
• Thickness of Mortar Joints are not also uniform.
• Bricks are not perfectly laid horizontally &
vertically
• Opening in walls
• Improper staggered joints
• Use of unwanted Brick bats
1. These resulted in cumulative effect &
concentration of stress in particular section of
wall is more than other section.
Structure Repairs & Rehabilitation
Corrective Measures For Load Bearing Wall
Building
• Therefore Shifting of Window, Door ,Inbuilt
construction of Almirah should be carried out
with due consideration to IS code 13828:1993
• Proper Bearing to lintel over brick work to avoid
diagonal cracks & it can be done in retrofitting
work.
• It is advisable to keep window width as less as
feasible while height can be increased with fixed
glass pans on top portion as per slide 41.
Structure Repairs & Rehabilitation
Importance Factor(I) Depend Upon
• Functional Use Of Structures
• Hazardous Consequences Of Its Failure
• Post Earthquake Personal needs
• Historical Value
• Economic Importance
• School Building Have “I” value=1.5
“I” value
1.5
Zone
Building Retrofitting need
II
III
IV
V
C
D
E
E
Structure Repairs & Rehabilitation
Elevation : Distance b1 to b8 changes as per Building
Retrofitting l Need
l
1
2
b8
t
3
h3
b2
b1
2
1
b5
b3
h2
h1
b4
b4
2
b4
b6
b7
1
2
b4
h2
b5
Structure Repairs & Rehabilitation
Table :Size, Position Of Opening In Above Figure
Description
Building Retrofitting Need/Category
A,B,C
230 mm
`b6 (Minimum)
(b1+b2+b3)/l1
; (b6+b7)/l2 =
D
600 mm
0.46 ( For one Storeyed
0.42 ( For one Storeyed
Building )
Building )
0.37 ( 2 & 3 storeyed
Building)
0.33 (2 & 3 storeyed
Building)
`b4
450 mm
500 mm
`h3
(minimum)
`b8
600 mm
600 mm
900 mm
900 mm
Structure Repairs & Rehabilitation
• Strengthening Of Window When Its Position Is
Not As Per Table Above Slide No 42.
60
30
75
6 Ø @ 150
150
X
Window
Two Nos
HYSD Bars
Section X-X
X
Structure Repairs & Rehabilitation
Strengthening Arrangements Recommended For
low Strength Masonry Building
b = Lintel Bend
C = Roof Bend, Gable bend
d = Vertical steel at corners & junctions of wall
f = Bracing in plan at tie level of Pitched Roofs
g = Plinth band
For Building of Category ‘B’ in two storey
constructed with stone masonry in weak mortar,
provide vertical steel of 10 mm dia in both storey.
Structure Repairs & Rehabilitation
Strengthening Arrangements Recommended For
Elements of low Strength Masonry Building
Building
Category
A
B
C
D
Number Of Storey
Allowed
One, Two, Three
storey
One & Two Storey
Three Storey
One storey
Two & three storey
One & Two Storey
Strengthening
To Be Provided
`b, c ,f ,g
`b, c ,f ,g
`b, c, d, f, g
`b, c ,f , g
`b, c, d, f, g
`b, c, d, f, g
Structure Repairs & Rehabilitation
• Seismic wave propagation increases as height
of wall/structure increases.
• Seismic wave expansion pushes bricks of
corner of wall out of building.
• Movement of Seismic wave through joints of
similar or dissimilar component of building
,makes joint open, resulting in falling of
component of the building.
Structure Repairs & Rehabilitation
Possibility For Old Masonry Structures Strength
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Plinth Belt in lieu of plinth band
Lintel level belt in lieu of band
Roof level/ gable level band
Corner steel
Shape, Size & location of Window In Wall
Wall length to Height Ratio
Cross wall/ Brick Pillar/counter fort
Structure Repairs & Rehabilitation
Reinforced band on top of gable wall
It will reduce bending of gable wall
Structure Repairs & Rehabilitation
In long walls introduce buttress
to strengthen it.
Structure Repairs & Rehabilitation
Low Strength Masonry Building Retrofitting
For Brick Masonry Structure
• Height of the building in B.W. shall be restricted to
the following.
1. For retrofitting category of building A,B,C up to3
storey with flat roof or 2 storey plus Attic for
pitched roof.
2. For category D up to 2 storey with flat roof or one
storey plus Attic for pitched roof.
where each storey height shall not exceed 3.0 m.
Cross wall spacing should not be more than 16
times the wall thickness
CONTD.
Structure Repairs & Rehabilitation
3. Minimum wall thickness in brick masonry shall
be one brick for one & two storey construction,
while in case of three storey, the bottom storey
wall thickness is one & half brick.
4. Use brick from kiln only after 2 weeks when
work is in summer & 3 week when work in
winter.
5. Use leaner mortar preferably also adding lime
for repairing cracks in particular& in masonry in
general. It can be 1:1:6,1:2:9,1:3:12 as per need.
Structure Repairs & Rehabilitation
For Stone Masonry
• Height of the building in Stone Masonry shall
be restricted to the following
1. For retrofitting category of building A,B,—2
storey with flat roof or 1 storey plus Attic for
pitched roof .In case cement sand mortar 1:6,
the building up to 2 storey plus Attic for
pitched roof.
2. 2. For category C,D– 2 storey with flat roof or
2 storey plus Attic for pitched roof with
Cement sand mortar or 1 storey plus Attic for
pitched roof with lime- sand or mud mortar.
CONTD.
Structure Repairs & Rehabilitation
3. Maximum wall thickness in
stone masonry shall be 450 mm
& preferably 350 mm. ,
• Each storey height shall not
exceed 3.0 m and span of walls
between cross wall is limited to
5.0m
Structure Repairs & Rehabilitation
• Cross wall connection In steps
SECOND LIFT
600 mm
600 mm
FIRST LIFT
Structure Repairs & Rehabilitation
Wall to wall joints are to be made
by building wall ends in steps form
Structure Repairs & Rehabilitation
Vertical reinforcement within the masonry in
corners increases wall’s capacity to withstand
Horizontal cracks due to bending.
Structure Repairs & Rehabilitation
In Each Layer Staggered Toothed Joint
Y A
X
PLAN
115 mm
230 mm
A
B
Elevation Showing
Vertical Joints In
Staggered Layer
450 mm
230 mm
View-X At A-A
B
View- Y At B-B
Structure Repairs & Rehabilitation
Recommended Longitudinal steel in
Reinforcement Concrete Bends
Span of Band
Between
Cross Wall
Building
Category
“B”
In MM
No. Of Dia.
Bars
Φ
MM
5 or Less
6
7
8
2
2
2
2
8
8
8
10
Building
Category
“C”
No. Of Dia.
Bars
Φ
MM
2
2
2
2
8
8
10
12
Building
Category
“D”
No. Of
Bars
2
2
2
4
Dia.
Φ
MM
8
10
12
10
Building
Category
“E”
No. Of
Bars
Dia.
Φ
MM
2
2
4
4
10
12
10
12
Spacing Of Tor Ring/Links 6 mm @ 150 mm Or 8 mm @ 200 mm
Bands Thickness vary 75 mm for 2 bars & 150 mm for 4 bars
Structure Repairs & Rehabilitation
• Steel Profile In Band At Corner & Junction
Lap= 50 ф
Staggered
Structure Repairs & Rehabilitation
≤ 450
Pair of stone
with length= ¾
of wall
thickness
≤ 1200
≤ 1200
≤ 1200
Bonding Elements
A. Wood Plank
( 38x38x450 mm)
B. R.C.C. Block
(50x50x450 & 8 mm)
C. 8 or 10 mm Hook
or “S” shape bent Bar
Plan showing Through Stone
Through stone = Bonding Element
900 mm For Second Height
600 mm For First Height
Structure Repairs & Rehabilitation
“S” shaped steel rod placed in a through hole in
random rubble wall and fully
encased in concrete
Structure Repairs & Rehabilitation
Pair of stone
with length= ¾
of wall
thickness
≤ 450
≤ 1200
≤ 1200
≤ 1200
CL
Plan showing Center bar in Casing
Casing in every 0.6 m is lifted & M15 or
Mortar 1:3 is Compacted around bar.
Structure Repairs & Rehabilitation
Cross bracings
at ends of room
X
Three Nails 5Ø
•drilled in
member
made by
splitting
bamboo in
two part
• Half Split Bamboo Ties To Rafter
• Brace the Rafter to 50 mm Dia Bamboo (B)
• Seismic Bend & Rafter should be tied Properly
B
Structure Repairs & Rehabilitation
Diagonal tying on the upper or underside of the
roof Prevents roof from getting distorted and
damaged
Structure Repairs & Rehabilitation
Installing multiple strands of galvanized iron wires
pulled and twisted to pretension
Structure Repairs & Rehabilitation
Vertical steel at corners and junction of walls up
to 350 mm thick should be embedded in plinth
masonry of foundations, bands, roof slab as per
table
Nos Of Storey Storey
One
Diameter Of H & D Single HYSD Bar in mm at each critical
Section (for above 350 mm, increase bar dia proportionally
Category C
Category D
--------
Nil
10
Top
10
10
Bottom
10
12
Top
10
10
Middle
10
12
Bottom
12
12
Two
Three
Structure Repairs & Rehabilitation
3/4B
One Brick Thick
One & Half Brick Thick
-------- Contain One Bar At Centre
Structure Repairs & Rehabilitation
Seismic Belts & closing a opining with pockets made
in jams of masonry.
Pockets
Structure Repairs & Rehabilitation
Encasing masonry column in cage of steel rods and
encased in micro concrete.
Structure Repairs & Rehabilitation
Anchoring the roof rafters and trusses with steel
angles or other means
Structure Repairs & Rehabilitation
Weld mesh belt approximately 220mm wide all
around the openings and anchored to masonry wall
and encased in cement mortar
Structure Repairs & Rehabilitation
Vertical deformed steel encased in concrete bar from
foundation to roof, anchored to both masonry walls
at wall junctions with special connectors.
Structure Repairs & Rehabilitation
Seismic belt in lieu of Seismic Band is made of weld
mesh approximately 220mm wide anchored to
masonry wall and encased in cement mortar.
Structure Repairs & Rehabilitation
Use smaller glass panes for windows Prevents the
shattering of glass in earthquake and cyclone
Structure Repairs & Rehabilitation
Anchoring roof to wall &, reducing roof
overhangs,
prevent the roof from getting blown off
Structure Repairs & Rehabilitation
Prolonged flooding can weaken the mortar,
especially if it is mud mortar, and hence,
the wall, causing cracking in walls or collapse.
Structure Repairs & Rehabilitation
If the ground is sandy in which the foundation is sitting, then
high speed flood/surge water can scour the land around and
under the foundation of your school, leading to settlement
and/or cracking of the wall.
Structure Repairs & Rehabilitation
Simple erosion of wall near its bottom, or cracking,
plaster peeling off and settlement
in floor.
Structure Repairs & Rehabilitation
Too small Projection
Leaking Roof
Deficient bearing length of
More Than One
lintels
Story Building
Door &
Window
Opening to
large
Openings
to closer to
corner
Lack Of foundation
& plinth
Wall to high & too Long
Exposed walls without
plaster or Pointing
Vertical
Joint Without
Mortar
Unbroken joint at corner
Structure Repairs & Rehabilitation
Extensive cracking of walls caused by
differential settlement due to flood
Structure Repairs & Rehabilitation
High plinth level to avoid entering flood
Structure Repairs & Rehabilitation
Use of pilasters
strengthens
walls against
flowing water
If thatch is used, cover with waterproof
mud plaster
Use band
Projected Roof
below roof
m
Max 0.5 m
truss/rafter
Opening 1.2 m
From Corner
Buttress in
long wall
Waterproof
Damp proof
mud plaster
at Plinth
or cement
Foundation & plinth
plaster
Low height wall Maximum 8
Good bonding Mortar
times thickness
Structure Repairs & Rehabilitation
• This Presentation was focused on Low Strength Masonry
Buildings therefore for framed structures & rich cement
mortar building ,certain slides are in-valid. In next
Presentation this balance portion will be highlighted.
• This Presentation was aiming to provide some technical
input to site peoples so that we could point out any
doubtful detailing in drawings to Structural/Architectural
Designer.
• It is possible that features of Flood, Heavy Rain fall,
Cyclone, earth quack may collide but We have to look
priority of our geographical requirement.
Thank You

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