Formwork for concrete structures

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👉TYPES OF STAIRS @engineer03
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➡Depending upon the various arrangement of steps, stairs can be classified under following categories:
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1. STRAIGHT STAIR:
In this stair, all the steps are arranged continuously
along in one direction. One flight may be split into
one or more than one flight by interposing a
landing. This stair can be used where narrow and
long space is available for a staircase such as
entrance, porch etc.
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2. DOGGED-LEGGED STAIR: This stair consists of two straight flights of steps with direct turns between them. This stair is very useful where the total width of the stair is just twice the width of the steps.
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3. OPEN NEWEL STAIR:
This type of stair consists of two or more flights
arranging a well or opening between the backward
and forward flights. When all the steps are difficult
to arrange in two flights, a short third flight of 3 to
6 steps may be provided along the direction
perpendicular to the hall. Open newel stair is mostly
adopted in the lift.
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4. GEOMETRICAL STAIR:
This is another type of open newel stair where the
open well between the forward and the backward
flight is curved. This stair may contain different
geometrical shape. Here the change in direction is
achieved by using winders.
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5. CIRCULAR STAIR:
In this type of stair, all the steps radiate from a newel or well hole, in the form of winders.
The circular stair is adopted at the back side of a building to access its various floors.
6. SPIRAL STAIR:
Spiral stair is very similar to a circular stair. It consists of individual steps or treads, connecting to a centre column. The overall diameter of the stair may range from 1 to 2.5 m.
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7. QUARTER-TURN STAIR:
The quarter-turn stair can be defined as the stairs
that are turned at 90 degrees with the help of level landing.
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8. BIFURCATED STAIR:
This type of stair is provided in modern public
buildings as well as residential buildings. In this stair, the flight is so arranged that there is a wide flight at the start which is sub-divided into narrow flights at the mid-landing. The narrow flights start from either side of the mid landing.
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👉Mix design can be divided into following two categories
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➡ 1. Design mix concrete
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➡ 2. Nominal mix concrete.
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1. DESIGN MIX CONCRETE:
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*When the proportions of concrete ingredients are decided by adopting certain established relationships (based on assumptions from a lot
of experiments) to produce the concrete it is known as design mix concrete.
*In design mix concrete, it is assumed that compressive strength of concrete is totally
dependent on the water- cement ratio.
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2. NOMINAL MIX CONCRETE:
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*When the concrete is produced by taking standard arbitrary proportions of concrete ingredients, it is known as nominal mix concrete. *This method is generally used when the quality control requirement for design mixes are difficult to execute. As we have explained for normal work, nominal mix concrete can be designed by taking cement, fine aggregate and coarse aggregate in
the ratio of 1 : n : 2n.
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👉ኣሁን ደሞ ስለ SHEAR WALL እንንገራቹ
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➡SHEAR WALLማለት የአግዳሚ ወይም horizontal load ተፅዕኖዎችን የሚቋቋሙልን ግድግዳዎች ናቸው፡፡
⏩ሺር ዎል የተባሉበትም ምክንያት የመሬት መንቀጥቀጥ በጎን አቅጣጫ ስለሚመጣና ዎሎቹ ላይ የሺር ተፅዕኖ ስለሚያሳድር ነው ( ሺር በ Thickness ትይዩ በሆነ አቅጣጫ እንደሚመጣ ልብ ማለት ይገባል፡፡
⏩Horizontal force የሆኑት Earth Quake እና Wind Load በዎሎቹ Thickness ትይዩ በሆነ አቅጣጫ ነው የሚመጡት):፡
⏩ሺር ዎሎች በትክክል ዲዛይን ተደርገው ትክክለኛ ቦታቸው ላይ ካልተቀመጡ ከጥቅማቸው ይልቅ ጉዳታቸው እጅግ ብዙ ነው::
ህንጻውን አፍራሽ ግብረ ሃይል ናቸው - ስለዚህ እንዴት ማስቀመጥ እንዳለብን ቀጥለን እንመልከት፡👇
1) አንድ ህንፃ ላይ የሚፈቀደው ትንሹ የሺር ዎል ብዛት ሶስት ነው፡፡ ቢያንስ-ሶስት
2) ሶስት ወይም ከዛ በላይ ሺር ዎሎች ካሉን የዎሎቹ አክሲሶች አንድ ነጥብ ላይ መገናኘት የለባቸውም::
3) ትይዩ እንዲሆኑ የሚፈቀደው ቢበዛ ለሁለት ዎሎች ነው፡፡ ሺር ዎሎች ከኮለንና ቢም ይልቅ የህንፃውን ጥንካሬ ወይም Stiffness ወደ ራሳቸው የመጎተት ከፍተኛ አቅም አላቸው ፤ እንደሚታወቀው የመሬት መንቀጥቀጥ act የሚያደርገው center of Mass ላይ ነው ፤ የመሬት መንቀጥቀጥን በተሻለ ሁኔታ ለመቋቋም ደግሞ የህንፃው ጥንካሬ ወይም Center of Stiffness የሚገኝበት ነጥብና የህንጻው Center of Mass
የሚገኝበት ነጥብ በተቻለ መጠን መቀራረብ አለበት ፤ እናም ስናጠቃልለው - በትክክል ያልተቀመጡ ሺር ዎሎች የህንጻውን Center of Stiffness ወይም ጥንካሬ ወደራሳቸው ሲጎትቱት ከ Center of Mass እንዲርቅ ያደርጉታል በመራራቃቸው የተነሳ እሽክርክሪት ፎርስ ወይም Torsion ይፈጠራል፡፡ Torsion ህንፃው እንዲፈርስ ያደርገዋል፡፡
▶የኒውተን ሶስተኛ ህግ ምን ይላል... “The forces of action and reaction between interacting bodies are equal in magnitude, opposite in direction and COLLINEAR” – ሁለት ፎርሶች Collinear force የሚባሉት ደግሞ በአንድ መስመር act ሲያደርጉ ነው፡፡
የመሬት መንቀጥቀጡ CM ላይ Act ሲያደርግ CS ደግሞ በሺር
ዎሎቹ ስለተጎተተ ሌላ ቦታ React ያደርጋል፡፡ በዚህ የተነሳ
Collinear force አይደሉም ማለት ነው፡፡ ስለዚህ Newton
Third Law ውድቅ ሆነ ማለት ነው፡፡ Action እና Reaction
በመጠንም ይሁን በአቅጣጫ እኩል ስለማይሆኑ ትርፍ balance ያልተደረገ force ይፈጠራል - Newton First Lawን ታሳቢ በማድረግ ህንፃው Equilibrium ላይ አይሆንም ማለት ነው፡፡
የኒውተን ሁለተኛ ህግስ ማን አለው የሚል ሰው ካለ - በመሬት
መንቀጥቀጥ ሳቢያ የሚፈጠረው ፎርስ ማለት የህንፃው ክብደት
ሲባዛ በእንቅጥቃጤው የሚፈጠር Acceleration ነው - ይህም
Newton Second Law ነው::
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⏩ ስናጠቃልለው ከጥፋት ለመዳን ሺር ዎልን ስናስቀምጥ ከላይ ያሉትን ሶስት ነጥቦች ተግባራዊ ማድረግ አለብን፡፡
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