cracks in buildings
TRANSCRIPT
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الشروخ الخرسانية أسبابها وعالجها -
وقد تكون هذه الشروخ. الشروخ الخرسانية ألسباب عديدة ومختلفة تحدث
المبنى وديمومة قد تؤثر في عمر على درجة من الخطورة
تصنيف الشروخ -
:ونميز منها( ألسباب غير إنشائية ) شروخ غير إنشائية -1
:شروخ االنكماش الحراري-
II. -شروخ االنكماش اللدن:
DRYING SHRINKAGE CRACKINGشروخ انكماش الجفاف -
NSDEFFERENTIAL THERMAL STRAI :فروق اإلجهاد الحرارية شروخ --
شروخ نتيجة التآكل -
:هناك نوعان يساعدان على تزايد تأثير عوامل التعرية على المنشأ الخرساني -
: تآكل حديد التسليح -1
نحر الخرسانة -2
الشروخ اإلنشائية- تتعرض الخرسانة المسلحة الجتهادات الشد عند تحميل المنشأ
. ، ولذلك تحدث شروخ في الكمرات في الجانب المعرض للشد تحت تأثير عزم االنحناء
التآكل والصدأ يتزايدان بسرعةحيث أم م2.2هذه الشروخ مقبولة إذا كان سمكها
.مم2.0عندما يزيد سمك الشرخ عن
هادات القصالشروخ نتيجة اجت -
وتحدث( التكسيح ) في اتجاه أسياخ التسليح (مائلة) وتكون شروخاً قطرية
بسبب عيوب في ترابط أسياخ الحديد ذات القطر الكبير مع الخرسانة ،
: قليل تكون هذه الشروخ ظاهرة بدرجة تشكل خطرًا مثل التسليحخاصة إذا كان غطاء
.يزداد اتساعها بصفة مستمرةشروخ عزوم االنحناء أو القص التي .1
شروخ تحدث في أجزاء الخرسانة المعروضة للضغط .2
. في المنشأ يعملوهذا ينبه إلى أن هناك سلوكاً غير عادي
تفتت الخرسانة في مناطق الضغط .3
(األعمدة أو الكمرات أو البالطات في الجانب المعرض للضغط )
.وهذه الحالة من أقصى درجات الخطورة على المنشأ
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a) Temperature and drying shrinkage cracks.
With few exceptions, newly placed concrete has the largest volume
that it will ever have. Shrinkage tendency is increased by excessive
drying and/or a significant drop in temperature that can lead to random
cracking if steps are not taken to control the location of the cracks
by providing control joints.
When the footing and wall are placed at different times, the shrinkage
rates differ and the footing restrains the shrinkage in the wall causing
cracking. Lack of adequate curing practices can also result in cracking.
b) Settlement cracks.
These occur from non-uniform support of footings or occasionally from
expansive soils.
c) Other structural cracks.
In basements these cracks generally occur during backfilling,
particularly when heavy equipment gets too close to the walls
d) Cracks due to lack of joints
or improper jointing practices.
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The bottoms of beams are most often affected by the intrusion of salts and by
water that flows through expansion or construction joints. Heavily reinforced with large
diameter reinforcing steel, successful repairs should fully expose the rebar and adjacent
stirrups. After coating the reinforcing steel, forms are constructed to pump in concrete under
pressure and leaking joints are repaired to prevent future deterioration.
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االنشائية والتصدعات التشققات
:يوجد انواع عديدة من التصدعات والتشققات التي تظهر في بالطات االسقف وهي تصنف كاالتيتشققات سطحية صغيرة توجد اعلى البالطات ولها انواع عديدة اما انها تشققات نتيجة االنكماش الناتج من التبخر او -1
.التشققات الحرارية عطاف وغالبا ما تكون من االحمال الزائدة أو سو في التنفيذ او ف مقاومة القص واالنعالتشققات الناتجة من ض -2
.التصميم .تشقات نتيجة الهبوط في العناصر االنشائية التي تحمل البالطات -3
تشققات تسرب المياه
: تسرب المياه من بالطات االسقف له اسباب عديدة ومنها
اعلى البالطاتعدم وجود صبة ميالن مما يسمح بتجمع المياه - 1
(عمل البالطة على مرحلتين دون معالجة ذلك) وجود فواصل صب -2
تسرب المياه من خالل الفواصل بين االسقف والجدران -3
عدم وجود نظام عزل مائي ، او وجود اضرار في نظام العزل -4
سوء تركيب االنابيب وعدم وجود موانع تسرب -5
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لوكالتشققات الظاهرة في الجدران الب
الناتجة من بناء الطوب قبل صب الجسورواالسقف
للتصلبوعدم انتظار الفترة الكافية لتأخذ خرسانة الجسور واالسقف وقتها الكافي
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Various Reasons of Cracks in Buildings
- Cracks can occur due to chemical reactions
in construction materials,
changes in temperature and climate,
foundation movements and settling of buildings,
environmental stresses like nearby trains, earth quakes etc.
Faulty design, bad quality materials,
wrong method of construction,
weather effects and lots of wear and tear can create cracks in
walls, floors and ceilings.
Here are given various reasons of cracks and their
prevention techniques.
-Elastic Deformation
When the walls are unevenly loaded, due to variation in stresses
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in different parts of wall the cracks are formed in walls. When two
materials having wide different elastic properties are built
together under the effect of load, different shear stresses in these materials create cracks at the junction. Dead and live loads cause
elastic deformation in structural components of a building.
Prevention
Create slip joints under the support of RCC slab on walls. Masonry
work on RCC slabs and beams should not be started before drying
RCC slab and beam. Provide horizontal movement joints between
the top of brick panel and RCC beam/slab.
- Thermal Movement
All materials expand on heat and contract on cool. Thermal
movement in components of structure creates cracks due to tensile
of shear stresses. It is one of the most potent causes of cracking in
buildings and needs attention.
Prevention
Construct joints such as construction joints, expansion joints,
control joints and slip joints. The joints should be planned at the time of design and be constructed carefully.
- Chemical Reaction
Chemical reactions in building materials increase their volume and
internal stress causes cracks. The components of structure also
weaken due to chemical reactions. Some common instances of
chemical reactions are following.
Sulphate attack on cement products
Carbonation in cement based materials
Corrosion of reinforcement in concrete
Alkali aggregate reaction
Prevention
Use dense and good quality concrete i.e. richer mix of cement concrete 1:1.5:3 to prevent cracks. Repair corrosive cement
concrete surface by ‘guniting’/ injecting technique after removing
all loose and damaged concrete and cleaning reinforcement from
all rust also.
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- Shrinkage
Most building materials expend when they absorb moisture from
atmosphere and shrink when they are dry. Cement made materials
shrink due to drying up of the moisture used in their construction. The factors causing shrinkage in cement concrete and cement
mortar and their preventions are following.
1. Excessive Water
The quantity of water used in the mortar mix can cause
shrinkage. Vibrated concrete has less quantity of water and
lesser shrinkage than manually compacted concrete.
Prevention
Use minimum quantity of water required for mixing cement
concrete or cements mortar according to water cement ratio. Never allow cement concrete work without mechanical mix and
vibrator.
- Quantity of Cement
As a general rule, the richer the mix is, the greater the
shrinkage/drying will be.
Prevention
Do not use excessive cement in the mortar mix.
- Un-graded Aggregate
Aggregate can cause shrinkage also. If un-graded and fine
material/aggregate is used in cement concrete and cement mortar
which requires more water and can cause greater shrinkage. Prevention
Use largest possible aggregate and ensure good grading of
materials. The use of water according to required workability has
less shrinkage because of reduction in the porosity of hardened concrete.
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.
- Excessive Fine materials
Fine materials take more surface area and require more water for
mix. The use of excessive fine materials i.e. silts; clay and dust in
aggregate create more shrinkage.
Prevention
Do not use fine materials containing silt, clay and dust. Use coarse
sand/fine aggregate in cement concrete and cement mortar mix which has silt and clay less than 4%. Use coarse aggregate and
fine aggregate after washing to reduce silt contents.
- Foundation Movement and Settlement of Soil
Shear cracks occur in buildings when there is large differential
settlement of foundation due to any of following causes.
Unequal bearing pressure under different parts of the structure Bearing pressure being in excess of safe bearing strength of the
soil
Low factor of safety in the design of foundations
Local variation in the nature of supporting soil
Prevention
The design of foundation must be based on sound engineering
principles and good practice.
- Vegetation
The roots of trees located in the vicinity of a wall can create cracks
in walls due to growth of roots under foundation. The cracks occur
in clay soil due to moisture contained by roots.
Prevention
Do not let trees grow too close to the buildings, compound walls etc. Remove any saplings of trees as soon as possible if they start
growing in or near of walls etc.
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A crack of this nature definitely warrants further investigation. While the
crack itself is vertical there is movement along the horizontal plane, which
indicates a shifting of the foundation or ground beneath.
I have cracks in the drywall on some of my interior walls. What
caused this?
Cracks in your interior drywall are a sign of a settling foundation.
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Structural cracks
Cracks in concrete beams due to increased shear stress
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Cracks in concrete beams due to corrosion or insufficient concrete cover
Cracks parallel to main steel in case of corrosion in beams
Cracks due to increased bending stress in beams
Cracks due to compression failure in beams
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TYPES OF CRACKS IN CONCRETE COLUMNS
TYPES OF CRACKS IN REINFORCED CONCRETE COLUMNS
1. Cracks due to eccentricity in concrete columns
2. Cracks due to corrosion of reinforcement in concrete columns
3. Cracks due to increased column load
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TYPES OF CRACKS IN REINFORCED CONCRETE SLABS
TYPES OF CRACKS IN REINFORCED CONCRETE SLABS
1. Cracks in reinforced concrete slabs due to Steel Corrosion (cracks parallel to steel bars)
2. Cracks in reinforced concrete due to shrinkage of concrete
3. Cracks in reinforced concrete due to increased load on the slab
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4. Cracks in reinforced concrete due to sulphate attack
5. Cracks in reinforced concrete due to alkaline aggregates
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The figure shows the concrete deformations and cracks. They are presented in a very
large scale to provide a thorough understanding of the way the members behave. In
reality they are so small that they are not visible to the human eye.
The tensile stresses generated in some areas of concrete cause the formation of
cracks; therefore in those areas the necessary reinforcement is placed. When the
cracks are perpendicular to the axis of the member, longitudinal reinforcement is
placed i.e. rebars that prevent the expansion of the hairline cracking.
When the cracks are diagonal, transverse reinforcement i.e. stirrups is placed to
control them.