Building Quality Structures

Different types of structures we see around

Our aim is to build a quality design with

low cost.

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

Dynamic Load: WindRain PeopleLoading/Unloading

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

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

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

Weight of 1 truss (N) = 100 kg x 10 = 1000 N

1. Load on Truss10m

4m



8000N

Total weight on trusses (N) = 8000 N + 3000 N = 11000 N

1. Load on Truss 10 m

4 m



8000 N

1000 N 1000 N 1000 N

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

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

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

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.

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.

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).

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.

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

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

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

Wind Force


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)


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

Building Quality Structures

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