👉Prestressed Concrete

🌟A member where the concrete is prestressed by the longitudinal reinforcing steel(tendons) before being subject to external loading is described as prestressed concrete. The tendons are of high strength steel (1000 to 2000MPa) and the concrete, a also at high strength (50 to 90MPa).

🌟There are two methods of manufacturing

1⃣Pretensioning the tendons before casting the concrete
2⃣Post tensioning the tendons after casting the concrete

🌟A pretensioned member is manufactured by, first, pretensioning the steel tendons over the length of the casting bed, and anchoring the steel to rigid anchor blocks at either end. The tendons are generally in the form of straight high tensile steel wires varying in diameter from 2 to 7 mm. The concrete is then cast around the tendons using shuttering to form the required shape of cross section of the member. Generally within 3 days, using accelerated curing techniques, the concrete has gained sufficient strength to be able to transfer the prestressing force to the concrete by releasing the anchorages. The shuttering is then removed and the casting bed can be used again.

🌟Post tensioned member is manufactured by first preparing the shuttering which supports sheaths or ducts. The ducts contain unstressed tendons in the form of straight or curved cables, or bars, which are free to move in the direction of their length but are restrained to prevent movement transversely. The concrete is then poured into the mould and allowed to gain strength. There is less urgency in this methods of manufacture and the shuttering is removed after a few days. Later, when the concrete has matured the steel is stressed by jacking against the ends of the beam and anchored using wedges for cables, or nuts on threaded rods for bars. The method is suitable for members of different cross section and for members which are cast in place on the construction sites where road access us difficult.

🌟The advantages of prestressed concrete as compared with ordinary reinforced concrete are

✅Reduced self weight of members
✅No cracks at service load and consequently better durability
✅Increased shear resistance

🌟The disadvantage of prestressed concrete as compared with ordinary reinforced concrete are

❎Increased cost of materials and shuttering
❎Greater supervision required to ensure concrete strength and magnitude of prestress forces,
❎Design calculations are more extensive.  
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👉The Role of estimating in the construction industry

🌟Estimates serve a number of different functions in the construction process.once the design of the project is underway,budget amounts can be established for the various elements of the project using procedures for a preliminary estimate.these cost budgets are compiled in a cost plan are verified from time to time during the design phase using more accurate estimating methods based on the specific design details that emerge in this phase of the project.

📌PROJECT PHASES

》program phase...owner considers the feasibility of the purposed project.

》schematic phase...designers prepare preliminary sketches of the project.

》Design development phase...the scope of work of the project is developed.

》contract documents phase...drawings and specifications are finalized these define the scope of work that forms the basis of the  contractor's bid.

》contractor selection phase...contractor's compete for the job and the successful contractor is awarded the contract.

》construction phase...construction work is executed.              

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👉Dynamic compaction is a method that is used to increase the density of the soil.

🌟The process involves dropping a heavy weight repeatedly on the ground at regularly spaced intervals.

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1⃣Smooth wheel rollers (or smooth drum rollers)

🌟Smooth wheel rollers that can also create vertical vibration during compaction. Smooth wheel rollers are suitable for proof rolling subgrades and for finishing the construction of fills with sandy or clayey soils. They provide 100% coverage under the wheels, and the contact pressure can be as high as 300 to 400 kN/m2. However, they do not produce a uniform unit weight of compaction when used on thick layers.

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2⃣Pneumatic rubber tired rollers

🌟Pneumatic rubber tired rollers are better in many respects than smooth wheel rollers. Pneumatic rollers, which may weigh as much as 2000kN, consist of a heavily loaded wagon with several rows of tires. The tires are closely spaced four to six in a row. The contact pressure under the tires may range up to 600 to 700 kN/m2, and they give about 70 to 80% coverage. Pneumatic rollers, which can be used for sandy and clayey soil compaction, produce a communication of pressure and kneading action.

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3⃣Sheeps foot rollers

🌟Sheepsfoot rollers consist basically of drums with large numbers of projections. The area of each of the projections may be 25 to 90 cm2. These rollers are most effective in compacting cohesive soils. The contact pressure under the projections may range from 1500 to 7500kN/m2. During compaction in the field, the initial passes compact the lower portion of a lift.

During compaction in the field, the initial passes compact the lower portion of a lift. Later, the middle and top of the lift are compacted.

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4⃣Vibratory rollers

4⃣Vibratory rollers are efficient in compacting granular soils. Vibrators can be attached to smooth wheel, pneumatic rubber tired or sheepsfoot rollers to send vibrations into the soil being compacted.

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💫የነባር እና የአዳዲስ ስራ ተቋራጮች እና ማህበራት  ምዘገባ ለ 5 የስራ ቀናት መራዘሙን የሚገልፅ ማስታወቂያ፡-

🚧የአዲስ አበባ ቤቶች ልማትና አስተዳደር ቢሮ የቤቶች ልማት ኮርፖሬሽን ከቤት ልማቱ ጎን ለጎን ለበርካታ ዜጎች የስራ ዕድል በመፍጠር በኢኮኖሚው ተጠቃሚ ሲያደርግ የቆየና እያደረገም ይገኛል፡፡

🚧በዚህም መሠረት ኮርፖሬሽኑ በቀጣይ በሚኖረው የግንባታ ፕሮጀክቶች በዘርፉ የተሠማሩ ስራ ተቋራጮችንና ማህበራትን አሳታፊ አድርጎ ለመስራት ያሰበና ለዚህም ይረዳው ዘንድ በከተማችን ያሉትን የስራ ተቋራጮችንና ማህበራትን በመመዝገብ መረጃዎችን አደራጅቶ መያዝ እና መመልመል አስፈላጊ ሆኖ በማግኘቱን በቅርቡ በተቋሙ ማህበራዊ ድረ-ገጽ ምዝገባ ማካሄዱ ይታወቃል፡፡

🚧ይሁንና ምዝገባው በተለያየ ምክንያት ያለፋቸው እና ያልሰሙ በመኖራቸው እና ባቀረቡት ቅሬታ መሰረት ለነባር እና አዳዲስ ተመዝጋቢዎች ከቀን 06/11/2015 - 11/11/2015 ዓ.ም ከቀኑ 12:00 ሰአት ድረስ ለለተከታታይ አምስት የስራ ቀናት online ምዝገባው መራዘሙን እየገለጽን ከዚህ በታች የተቀመጠውን ማስፈንጠሪያ (Link)

http://aahdc.gov.et በመጫን እና የሚጠይቀውን መረጃ በአግባቡ በማስገባት መመዝገብ የምትችሉ መሆኑን እናሳውቃለን፡-

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🚧በተቋማችንና በተለያዩ ቅርንጫፍ ፅ/ቤቶቻችን ስር ከ2006 ዓ.ም ጀምሮ የስራ ትስስር ተደርጎላችሁ ስትሠሩ የነበራችሁ ስራ ተቋራጮችና ማህበራት ነባር በሚለው ስር ምዝገባችሁን ማድረግ ያለባችሁ ሲሆን፤

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🚧ከዚህ በፊት በተቋማችንም ሆነ በቅርንጫፍ ፅ/ቤቶቻችን ስር ምንም ዓይነት የስራ ትስስር ያልተደረገላችሁ አዲስ በሚለው ስር ምዝገባችሁን ማካሄድ ትችላላችሁ፡፡

👉ለምዝገባ አስፈላጊ ማስረጃዎችን በድጋሚ ለማስታወስ ያህል፡-

- የታደሰ ንግድ ፍቃድ
- የግበር መክፈያ መለያ ቁጥር( Tax    
   Identification Number- TIN.)
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- የብቃት ማረጋገጫ ሰርተፍኬት
- የስራ ልምድ ከ1-2 ገፅ በማይበልጥ
  በዝርዝር ይጠቀስ
- የስራ ልምድ ክብደት በገንዘብ ሲቀየር 
   የሚያሳዩ መረጃዎች
-  እና ሌሎች ስራ ተቋራጩን እና
   ማህበራቱን የሚገልጹ ሰነዶችን   ናቸው

📌ማሳሰቢያ፡-

👉 ከስራ ዕድል ፈጠራ ጋር በተያያዘ ከሚመለከተው አካል በሚላከው መረጃ መሠረትና በተቋማችን ባለው መረጃ መሠረት ወደ ስራ ሲገባ በነባር መመዝገብ እያለባችሁ በአዲስ ተመዝግባችሁ የተገኛችሁት ላይ እንዲሁም በሁለቱም (በነባርም፣በአዲስም) ተመዝግቦ የሚገኝ ስራ ተቋራጭም ሆነ ማህበራት ላይ እርምጃ የሚወሰድ መሆኑን ከወዲሁ ለማሳወቅ እንወዳለን፡፡

👉ከዚህ በፊት በነበረው ምዝገባ ማለትም እስከሰኔ 27/2015 ለተከታታይ 15 ቀን ሲደረግ በነበረው ምዝገባ የተመዘገባችሁ በዚህ ምዝገባ ማድረግ የማይጠበቅባችሁ መሆኑን እንዲሁም

👉አንድ ተቋራጭ ወይም ማህበር ከአንድ ጊዜ በላይ መመዝገብ የሌለበት መሆኑን እያሳወቅን ማንኛውም ይህንን ማሳሰቢያ ተላልፎ የተገኘ ተመዝጋቢ ከምዝገባው የሚሠረዝ መሆኑን ከወዲሁ እናሳውቃለን።

📍የአዲስ አበባ ቤቶች ልማት እና አስተዳደር ቢሮ የቤቶች ልማት ኮርፖሬሽን ነው

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👉Commonly asked questions in interviews

1⃣What is civil/Construction engineering?

Ans: It is a professional engineering discipline that deals with the construction, design and maintenance of the built environment, including public works for example roads, dams, bridges, buildings, canals, airports, sewerage systems, pipes and railways etc.

2⃣What are the different departments of civil engineering?

Ans: The departments of civil engineering are given:
🔸Structural engineering
🔸Geotechnical engineering
🔸Environmental engineering
🔸Water resource engineering
🔸Material science engineering
🔸Coastal engineering
🔸Transportation engineering
🔸Urban infrastructure
🔸Construction management
🔸Architectural engineering
🔸Railway engineering
🔸Fluid Mechanical

ETCONp

3⃣Which softwares are used in civil engineering?
Ans: The software used in civil engineering are:
🖥AutoCAD
🖥3DS max
🖥Prime Vera
🖥SAP 2000
🖥Microsoft project (word,
     Excel, PowerPoint etc.)
🖥Storm CAD
🖥Revit
🖥Eagle point
🖥ETABS
🖥MX Road

4⃣Please tell us the formula for calculating the unit weight of steel?
Ans: D2 / 162.162

5⃣What is slump test?
Ans: On construction site the slump test is used to measure the workability of concrete & it is measured by using a slump cone. On site, for high slump value, the water-cement ratio must be high. While for low slump value, the water-cement ratio is low.

6⃣Please tell us about workability of concrete?
Ans: Workability means the ease of placing and compacting concrete. Water cement ratio is directly proportional to the workability and inversely proportional to their strength.

7⃣What is the density of steel?
Ans: The density of steel is 7850 Kg / m3.

8⃣What is unit weight of cement? ETCONp
Ans: The unit weight of cement is 145 lb / ft3.

9⃣Please tell us about beam?
Ans: Beam is a structural member used to resist the applied load. Generally, beam is used to resist the shear force, vertical load and bending moment. Beam is horizontal element which is imposed on end points between walls, columns, pillars, foundations etc. In the past, beams were square, timber, metals, stone combination of timber and metal for example filth beam. Beams are used to carry vertical load. Beam is a flexible member which can resist the compression and tension force.

🔟What is column?
Ans: Column is a structural member which transmits the load of structure to the footing and soil. In other words, column is a compressive member that is constructed from concrete, reinforcement concrete, bricks and blocks etc. It is used to support beam or arches where the slab or ceiling rest.  It can be of many shapes such as rectangular, square, circular, hexagonal, octagonal etc. The column is arising from the base and rest on the foundation. It can be constructed of masonry or steel. It is design to resist the lateral force and for the purpose of wind or earth quack. A column might be used for decorative purpose.

🔟What is minimum number of bars used in circular column?
Ans: There can be a minimum of six 6 bars used in circular column. ETCONp

1⃣1⃣Please tell what is absorption of brick?
Ans: Bricks should not absorb more than 20 % of water, when it is immersed in water for at least one day or 24 hours.

1⃣2⃣Can water damage concrete?
Ans: Yes! Water can damage concrete. The defects that water induced in concrete are given below:
⚠️Water reduces the strength
     of concrete.
⚠️Water reduces the
     permeability for further
     water seepage.
⚠️It reduces the durability.

1⃣3⃣Difference between QA and QC?
Ans: QA stands for quality assurance, the activities designed to confirm that the development process and maintenance process is good to confirm a system will meet its objective.
QC stands for quality control, the activities designed to evaluate a developed work product.

1⃣4⃣Does brick grow every year?
Ans: No! the bricks do not grow every year. It grows because of the stuff that gets all over the bricks. that’s why its look like it grows every year.

...cont'd 👇

...cont'd
1⃣5⃣What is honey comb in concrete?* ETCONp
Ans: Honey comb is actually the voids or air pocks in concrete.

1⃣6⃣What is the distance between railway tracks?
Ans: The distance between railway track is 4 feet.

1⃣7⃣Why the pressure increases under soil?
Ans: Soil pressure increases because of its self–weight. The pressure of soil is directly proportional to the depth of soil. 

1⃣8⃣Name the structures which is subjected to the fatigue?
Ans: The structures which is subjected to the fatigue are:
🚩Bridges
🚩Hydraulic presses
🚩Burner trains

1⃣9⃣What is gravity flow?
Ans: When the fluid is flowing due to the force gravity but not on applied pressure is known as gravity flow.

2⃣0⃣What is Kip?
Ans: 1 Kip is equal to 1000 ponds.

2⃣1⃣What is aggregate?
Ans: The composite material used to resist the compressive stress. Aggregates are classified in two main types:
🔨Fine Aggregate
🔨Coarse Aggregate

2⃣2⃣Please tell us about soil reinforcement?
Ans: Soil reinforcement are used to improve soil strength and have ability to support more load.

2⃣3⃣Please tell the tallest man made structure?
Ans: The tallest man made structure is Burj ul khalifa. The height of burj ul khalifa is 828 meter. ETCONp

2⃣4⃣Which units are used for the measurement of concrete?
Ans: Cubic meter (m3), cubic foot (ft3), cubic yard (y3).

2⃣5⃣What are the causes of building collapse?
Ans: The causes of building collapse are:
🔸Weak foundation
🔸Passage of time
🔸Demolition
🔸Bombing
🔸Natural disaster

2⃣6⃣What is the final setting time of concrete? ETCONp
Ans: The final setting time of ordinary concrete is 10 hours.

2⃣7⃣What is initial setting rime of concrete?
Ans: The initial setting time of ordinary concrete is 30 minutes.

2⃣8⃣Please tell us about the types of beam?
Ans: The types of beam base on supports are:
〽️Simply supported beam
〽️Continuous beam
〽️Over hanging beam
〽️Double over hanging
〽️Cantilever beam
〽️Fixed beam
〽️Trussed beam

2⃣9⃣Please tell us about the types of load?
Ans: The types of load are:
🚼dead load
🚼live load
🚼snow load
🚼impact load
🚼Wind load
🚼Earth quacke
🚼Environmental load

3⃣0⃣What is minimum number of bars used in rectangular or square column?
Ans: 8 Eight minimum number of bars can be used in rectangular or square column.

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