Building Quality Structures
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Transcript of Building Quality Structures
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Building Quality Structures
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Different types of structures we see around
Our aim is to build a quality design with
low cost.
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What is a load?
Load is a force which applies on a structure. Any structure must withstand different types of forces or loads.There are two main types of loads:
Dead load: This is a permanent or stationary load which
can not be removed. For example: self weight of the structure
and
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Dynamic Load: WindRain PeopleLoading/Unloading
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We will study one example to understand the concept clearly. Imagine that we have to build a structure, a Tractor Shed of following dimensions.
10 m
4 m
9 m
5 m
Truss
Column
Foundation
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Main features which will carry the load are: The trusses – own weight and weight of the roofThe columns – own weight and weight of the
trusses The foundation – own weight and weight of the trusses and columns
Important rule: Always work from top to bottom
1. Truss
2. Column
3. Foundations
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1. Load on Truss10 m
4 m
Steel Sheet = 10kg/m2
Mass of 1 Truss = 100kg
Area of roof (m2) = 10 m x 4 m x 2 =80 m2
Mass of roof (kg) = 80 m2 x 10 kg/m2 = 800 kg
Weight of roof (N) = 800 kg x 10 = 8000 N
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Weight of 1 truss (N) = 100 kg x 10 = 1000 N
1. Load on Truss10m
4m
Steel Sheet = 10kg/m2
Mass of 1 Truss = 100kg
8000N
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Total weight on trusses (N) = 8000 N + 3000 N = 11000 N
1. Load on Truss 10 m
4 m
Steel Sheet = 10kg/m2
Mass of 1 Truss = 100kg
8000 N
1000 N 1000 N 1000 N
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2. Load on Column
5m
Mass of 1 Column = 10 kg/m
8000N
1000 N 1000 N 1000 N
Mass of 1 pole = 5 m x 10 kg/m = 50 kg
Weight of 1 pole = 50 kg x 10 = 500 N
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2. Load on Column
5 m
Mass of 1 Column = 10 kg/m
11000 N
500 N
500 N
500 N
500 N
500 N
500 N
Load on each column = 11000 N + 3000 N = 14000 N
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Weight of Foundations = 2000 kg x 10 = 20000 N
3. Load on Foundation
14000N
Load on Foundations = 14000 N + 20000 N = 34000 N
Mass of Foundation = 2000 kg
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Windflow over buildings
high pressure
low pressure
low pressure
The diagram illustrates how wind follows in a curved path as it flows over a building. The effect is the same as in a tornado; towards the centre of curvature, the pressure drops. The wind causes high pressure on the wall it hits, and low pressure on the wall behind the building.
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Greater the curvature, lower the pressure and greater the suction.
As can be seen, a square shaped building experiences large force, a pitched roof experiences less suction, and a domed roof experiences least force. Dome shapes have started being used in hurricane prone regions of America.
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So how do I calculate wind load?What are the things affect wind load?
Size of the building
Height of the building
Shape of the building
Area of roof
Region (some regions are more prone to wind than others)
Landscape (wind accelerates over hills, so a building on a
hill will experience higher loads than those in
valleys).
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Zone Wind speed
(m/s)
55
50
47
44
39
33
Maximum expected wind speed in various regions across India
Pabal – 39 m/s
Always check this type of map to see the max. expected wind speed in your area. You want to design a building which can survive the worst case scenario.
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Wind speed is affected by local terrain
Safety Factor
Design wind speed = 1.1 x 39 m/s = 43
m/s
If you are on a hill, increase the wind speed by multiplying it by 1.1
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Wind pressure is the force per square
metre on a surface
Wind Pressure
Pressure (N/m2) = 0.6 x windspeed2
= x x 430.6
1109 N/m2=
43
1m1m
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Wind force is the specific force on a particular
part of the building
Safety Factor: account for internal pressure changes with a safety factor of 2
Wind Force
Force (N) = Pressure (N/m2) x Area (m2) x Safety Factor
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Wind Force
Force (N) = Pressure (N/m2) x Area (m2) x Safety Factor
Force On Wall (N) = 1109 N/m2 x 45 m2 = 99810 N
Area Of Wall (m2) = 9 m x 5 m = 45 m2
9m
5m
Wind Pressure = 1325 N/m2
Safety Factor = 2Wind Force (N)
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Force (N) = Pressure (N/m2) x Area (m2) x Safety Factor
Force On Roof (N) =
1109 N/m2 x 40 m2 x 2 =
88720 N
Area Of Roof (m2) = 10 m x 4 m
= 40 m2
10m
4m
Wind Pressure = 1325 N/m2
Safety Factor = 2
Wind Force (N)
Wind Force