👉Borrow material and Selected material

🚧In construction, borrow material is a naturally occurring material used to create fill and structural elements, while selected material is a material chosen to meet specific project requirements:

💫Borrow material

🏷A naturally occurring material that's excavated from a borrow pit and used to create fill and structural elements like embankments.

⏺Borrow material is selected to meet the project's grading, stability, and load-bearing capacity requirements.

💫Selected material

🏷A material chosen to meet specific project requirements. When selecting construction materials, factors to consider include strength, durability, cost, availability, and climate.

⭐️When selecting a borrow area, it's important to consider the quantity and quality of the fill, as well as the type of equipment that will be used.

@etconp

👉Bleeding & Segregation in Concrete

🚧Bleeding

➡️Bleeding is a form of segregation in which water present in the concrete mix is pushed upwards due to the settlement of cement and aggregate.

➡️The specific gravity of water is low, due to this water tends to move upwards.

➡️Bleeding ordinarily occurs in the wet mix of concrete.

➡️The Prime factor for bleeding in concrete is the high dosage of Water cement ratio.

➡️Higher water-cement ratio weakens concrete and leads to excessive bleeding.

➡️The bleeding in concrete is not harmful if the rate of evaporation of water is equal to the rate of bleeding.

➡️Normal bleeding is quite good, and it enhances the workability of concrete.

➡️When the concrete is fully plastic, bleeding may not cause much harm. However, concrete is still in the plastic stage later it is subsidized and compacted.

🚧Segregation

▶️Segregation is the “Separation of constituent materials in concrete"

➡️In concrete technology segregation is of three types

⏺1. Separation of Coarse aggregate from the concrete mixture.

⏺2. Separation of Cement pastes from the concrete during its plastic stage.

⏺3. Separation of water from the concrete mix (Bleeding in concrete)

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👉ስለ STAIRS ትንሽ ጠቃሚ ሃሳብ እንማማር 👇

🚧Calculations for the construction of stairs, ramps and guards are set out in various national building regulations.

💫The guidelines here are based on German standards.

▶️Dwellings with no more than two flats must have an effective stair width of at least 0.80 m and 17/29 rise-to-tread ratio. Stairs which are not strictly covered by building regulations may be as little as 0.50m wide and have a 21/21 ratio.

⏺Stairs governed by building regulations must have a width of 1.00m and a ratio of 17/28.

⏺In high rise flats they must be 1.25 m wide

⏺The length of stair runs from 23 steps up to 18 steps --> @ Landing length = n times the length of stride + 1 depth of step (e.g. with a rise-to-tread ratio of 17/29 = 1 x 63 + 29 = 92 cm or 2 x 63 + 29 = 1.55 m).

⏺Doors opening into the stairwell must not restrict the effective width.

▶️The time required for complete evacuation must be calculated for stair widths in public buildings or theatres. Such staircases or front entrance steps are climbed slowly, so they can have a more gradual ascent.

▶️A staircase at a side entrance or emergency stairs should make a rapid descent easy.

▶️The experiences one has of ascending and descending stairs varies greatly with the stair design, for example there is a significant difference between an interior domestic design and a grand flight of entrance steps.

⏺Climbing stairs takes on average seven times as much energy as walking on the flat.

⏺From the physiological point of view, the best use of 'climbing effort' is with an angle of incline of 30° and a ratio of rise of:  rise of step/going of step; r/g= 17/29.

▶️The angle of rise is determined by the length of an adult's stride (about 61-64cm). To arrive at the optimum rise, which takes the least energy, the following formula can be applied: 2r+ g= 63cm (1 stride)

▶️In the dimensioning and design of flights of stairs, the function and purpose of the staircase is of primary importance, taking in the factors mentioned above.

▶️Not only is the gaining of height important, but also the way that the height is gained. For front door steps in frequent use, low steps of 16 x 30cm are preferable.

⏹However, stairs in a workplace, or emergency stairs, should enable height to be gained rapidly.

⏺Every main staircase must be set in its own continuous stairwell, which together with its access routes and exit to the open air, should be designed and arranged so as to ensure its safe use as an emergency exit. The width of the exit should be  greater than or equal tothe width of the staircase.

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👉እስቲ ኣሁን ደሞ ስለ lap length , Development length,Anchorage length ትንሽ እንንገራቹ።

🏷1. ላፕ ሌንግዝ (lap length) - ተፈላጊ የብረት (ፌሮ) ርዝመት
ውጥረትን (stresses) ከአንድ ብረት ወደሌላ የሚተላለፍበት ነዉ

⏺The lap length varies from member to member. Lap length for tension members = 40d

⏺Lap length for compression members = 50d Where, d = Diameter of bars.

🏷2. ደቨሎፕመንት ሌንግዝ (Development length) -ተፈላጊ
የብረት ርዝመት ውጥረትን (stresses) ከብረቱ ወደ ኮንክሪቱ የሚተላለፍበት ነው።

🏷3. አንኮሬጅ ሌንግዝ (Anchorage length) - ይህ ርዝመት አይነት በቂ የሆነ ደቨሎፕመንት ሌንግዝ (development
length ) በሌለባቸው በ Support / fixed ends ላይ provide የምናረገው ርዝመት ነው።

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👉High strength concrete

➡High strength concrete (HSC) may be defined as concrete with a specified characteristic cube
strength between 60 and 100 N/mm , although higher strengths have been achieved and used.

▶Strength levels of 80 to 100 N/mm and even higher are being used for both precast and in-situ work in All over the world.

▶The main applications for HSC in-situ concrete construction are in offshore structures, columns for tall buildings, long-span bridges and other highway structures

▶The main advantage is the reduction in size of compression elements and/or the amount of longitudinal reinforcement required.

▶The methods and technology for producing high strength concrete are not substantially different from those required for normal strength concrete.
The target water/cement ratio should be in the range 0.30–0.35 or even lower.

⭐️HSC can be produced with all of the cements and cement
replacements (additions).
A wide range of aggregates can be used though crushed rock aggregates (of suitably high crushing value) are preferable.
Superplasticisers / high range water reducers should be used to achieve maximum water reduction, although plasticisers may be adequate for lower strength HSC (C-60 to C-70)

⏺Silica fume (microsilica) or metakaoline can be used to enhance the strength at high levels (C80 and above), but is not needed generally at the lower end (C60 to C80).

💫The terms "High performance concrete" and "High strength concrete" are often taken to mean the same thing.

⏺However, as indicated, "High performance" strictly relates to a concrete that has been designed to have good specific characteristics, such as high resistance to chloride ingress or high abrasion resistance.

▶️As a result it may also have a high strength, but this is not the main consideration.

@etconp

👉Why don't we use circular beams in construction or in structures?

💫Before we look at the reasons, please have a look at the framed structure where the conventional Rectangular section has been adapted :                                                                                               
🚧1.Formwork

Very difficult It has to be made out of either MS sheets or Aluminum sections.

Fixing it horizontally is more challenging since the base of the beam form work shall be semi circular.

The conventional methods of supporting with wooden CHABI is not suitable.

The Formwork shall need to have a provision on the top for pouring concrete.

🚧2.The casting

Imagine that a conventional letter box is laid Horizontality and you have to pour concrete through the opening at the top.

The concrete has to be high slump concrete so that it moves to all crevices of the section.

Finishing the top portion of the beam shall be a highly skilled job.

🚧3. The de -shuttering :

It shall not be possible to first strike off the sides and then the beam bottom .

The form work shall have to be removed in two halves after the concrete attains the strength.

⭐️Hope you’re clear with certain difficulties associated with the circular sections.

@etconp