👉እስቲ ዛሬ ደሞ ስለ Cohesion ትንሽ እንበል.... @engineer03
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▶Cohesion – soil ፓርቲክሎች አንድ ላይ እንዲጣበቁ የሚያደርግ ፎርስ ነው የሚገለፀውም በ Kilo Newton ነው::
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Angle of Internal friction - አንድ soil ፓርቲክልን ብንወስድ
በራሱ ክብደት ወይም በሌሎች ፓርቲክሎች ምክንያት በሚፈጠር
ፍትጊያ (friction) ምክንያት Horizontal (H) እና Vertical
(V) ሎድ ተፅእኖ ውስጥ ይወድቃል - እነዚህን ሎዶች የሚቋቋመው በአካባቢው ያሉት ፓርቲክሎች Normal እና Shear (T) react ስለሚያደርጉ ነው… የነዚህ ፎርሶች Resultant (R) ከ ‘N’ ጋር የሚሰራው አንግል ነው Angle of internal friction.
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Angle of Wall friction – እንደ angle of internal friction ሆኖ ነገር ግን soil ፓርቲክሉና Slip ፕሌኑ ከተለያዩ ማቴሪያሎች ከተሰሩ angle of wall friction ይባላል፡፡ Lateral Earth Pressure ላይ Coulomb Method ይህንን የአንግል አይነት ይጠቀማል::
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Cohesion እና Angle of internal friction ትልቅ ነው ማለት Bearing capacity ትልቅ ነው ማለት ነው::
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👉 አሁን ደግሞ ስለ Foundation (መሠረት) ትንሽ እንበል... @engineer03
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▶Shallow Foundation-እነዚህን ፋውንዴሽኖች የምንጠቀመው አፈሩ ብዙም ሳይቆፈር በቅርብ ጥልቀት ጠንካራ የአፈር ሁኔታ ካለ ነው፡፡ ለመገንባት ትልልቅ ማሺኖች አያስፈልጉም ብዙ ችሎታም አይጠይቁም::
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Spread/ Pad/ Isolated Footing - አንድ ኮለን ብቻ ነው
support የሚያደርጉት- የሚመጣውን ፎርስ eccentricity መሰረት በማድረግ circular/ rectangular or square የሆነ ቅርፅ ሊኖራቸው ይችላል፡፡ ያለፌሮ ሊገነቡ ይችላሉ ለምሳሌ ፓዱን slopped በማድረግ::
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Combined Footing - ሁለትና ከዛ በላይ ኮለኖችን በአንድ ፓድ
support ለማድረግ ነው የምንጠቀምባቸው፡፡ እነዚህን
የምንጠቀመው ሁለት ተቀራራቢ Isolated Footing ካሉ ሁለቱን
አንድ ላይ combine በማድረግ ኮንክሪትም ፌሮም ሴቭ ማድረግ
እንችላለን፡፡ በተጨማሪም isolated ለመጠቀም property
limit ካለ እነዚህን መጠቀም እንችላለን:: 2 አይነት Combined
Footing አሉ- እነርሱም ፡-
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1. Rectangular Combined Footing – ይህንን የምንጠቀመው ሁለቱም ኮለኖች የሚሸከሙት ሎድ ተቀራራቢ
ወይም እኩል ከሆነ ወይም ትራፖዞይዳል ለመጠቀም የስፋት
ገደብ ካለ ነው።
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2. Trapezoidal Combined Footing - ሁለቱ ኮለኖች የሚሸከሙት ሎድ ልዩነት የተጋነነ ከሆነ ነው።
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Strap/ Cantilever Footing - ሁለት ፓዶችን በቢም በማያያዝ
ሎድ ከአንዱ ፓድ ወደሌላው እንዲተላለፍ ማድረግ እንችላለን፡፡
ቢሙ በራሱ ሎድ አይሸከምም ሎድ ያስተላልፋል
እንጂ…….እነዚህን የምንጠቀመው ኮለኖቹ ከ7 ሜትር በላይ ከተራራቁ combined footing ብንጠቀም ኢኮኖሚካል ስለማንሆን ፓዶቹን በቢም በማያያዝ እንደ combined footing
ልንጠቀምባቸው እንችላለን፡፡
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Mat/ Raft foundation - እነዚህን የምንጠቀመው መሬቱ
የመሸከም አቅሙ ትንሽ ከሆነና spread footing ስንጠቀም
የህንጸውን ስፋት ከ50 ፐርሰንት በላይ ከሸፈኑት ነው ….. አንዳንዴ
ግን spread footing ከ50 ፐርሰንት በላይ ቢሸፍኑትም ለ
spread footing negative reinforcement ስለማንጠቀም ከ Mat ይልቅ ኢኮኖሚካል ሊሆኑ ይችላሉ - ምክንያቱም Mat
negative & positive reinforcement ይጠቀማሉ፡፡ ማን ኢኮኖሚካል እንደሆነ ቼክ ማድረግ የኢንጅነሩ ድርሻ ነው፡፡
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♻️ ADMIXTURES ~~~~~~~~~~~~~~~~
➡Admixtures are the special ingredients added during concrete mixing to enhance the properties and performance of fresh concrete. Various types of
admixtures are available in the market which is
used in construction work.
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➡FUNCTION OF ADMIXTURES:
1. To accelerate or retard the setting time of fresh
concrete.
2. To improve the workability or flowability of
concrete.
3. To increase the strength and durability of
concrete.
4. To reduce the heat of hydration.
5. To reduce the segregation and bleeding.
6. To decrease the permeability.
7. To achieve other desired properties.
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➡TYPES OF ADMIXTURES:
1. ACCELERATING ADMIXTURES:
This admixture is added in concrete or mortar for
increasing the rate of hydration of hydraulic cement and for shortening the setting time. Calcium
chloride (CaCl2) is the most widely used
accelerating admixture.
2. RETARDING ADMIXTURES:
Retarding admixtures delay the initial rate of
hydration of cement and extend the setting time of
cement paste. This admixture can be used in high temperature and where the concrete has to be transported to a long distance. It is also suitable for using in grouting oil wells.
3. AIR-ENTRAINING ADMIXTURES:
Air entraining admixtures help to produce a certain
amount of air bubbles in the concrete mixture. The
main goal of this admixture is to increase the resistance against freeze-thaw degradation and cohesion. It also improves the workability of fresh concrete without changing the setting or the rate of hardening.
4. WATER REDUCING ADMIXTURES:
As the name suggest, water reducers are added to a concrete mixture, mortar or grout to increase the flow ability without increasing the water content.
▶Advantages Of Water Reducing Admixtures:
1. The rate of concrete placement is faster.
2. Strength, durability, density etc. are significantly improved.
3. Segregation, permeability, and cracking are reduced.
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➡SPECIAL ADMIXTURES:
1. Superplasticizing admixtures.
2. Corrosion-inhibiting admixtures.
3. Grouting admixtures.
4. Coloring admixtures etc.
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