Types of Loads on Structure

Types of Loads on Structure

Load:

The load can be defined as the applied force on structure members. Load that acts on structures can be broadly classified as horizontal loads and vertical loads.

The vertical loads are:

1. Dead load
2. Live load
3. Impact load

While the horizontal loads are:

1. Wind load
2. Earthquake load

The structure should be designed to safely bear the different types of applied loads & that structure should not face any kind of failure. For estimating the total load acting on the structure must be calculated before designing. There are different codes for calculating the total load.

• Indian standard code is: 875-1987.
• American standard code ASCE7: minimum design loads for building and other structures.

Loads have a tendency to cause stress, displacement, deformation in a structure which leads to failure in the structure or can cause structural problems.

Structural analysis means analysis of loads or to find/calculate the loads on the structure. It is a very important and major part of the designing of structure. A structure may be building, road, dam, spillway, bridge, culvert, retaining wall, etc. There are a lot of different types of loads that are applied on a structure. Some loads are permanent and some loads are temporary. Generally, the load is measured in “Newton”. Newton is represented by “N”.

Types of Loads on structure:

The load is broadly classified as vertical load and horizontal loads:

Vertical Loads

The type of load that is applied on a structure in a vertical direction is called a vertical load. The vertical load is further classified into the following types:

1. Dead Load
2. Live Load
3. Environmental Load
4. Snow Load
5. Impact Load

Dead Load

The load that is constant in magnitude and fixed in location throughout the lifetime of the structure is called Dead Load. It is a permanent load and cannot be moved from the applied surface because it is a part of the structure itself.

It can be calculated with good accuracy from the design configuration, density of the material, and dimension of structure members. For example in a house or building, slabs, beams, floor & ceiling are included as dead loads. To find the total load, the “1.2” coefficient should be multiplying with the dead load. The equation for the total load is;

W = 1.2 (D.L) + 1.6 (L.L)

• L indicates the dead load
• L indicates the live load

For culverts and bridges, the dead loads are sidewalks, girder, curbs, wearing surface, and other suspended loads. Here is the list of materials with their density.

S.No	Material	Density(Kg/m3)	S.No	Material	Density(Kg/m3)
1	Water	1000	9	P.C.C concrete	2400
2	Steel	7850	10	R.C.C concrete	2500
3	Silt	2100	11	Ash white	670
4	Cement	1440	12	Ash black	540
5	Bamboo	300-400	13	Asphalt	721
6	Clay soil	1900	14	Cement mortar	2080
7	Sandstone	2000	15	Lime	640
8	Shale	2500

Let’s look into an example of how to find the dead load. For example, there is a beam of R.C.C & the density of R.C.C is 25 KN/m³ and the volume or dimension of the beam is 10 m³.

The equation for calculation of the dead load is:

Dead Load = V x d

• V indicates the volume of the structure
• d indicates the density of the material

For calculating dead load, simply multiply density with its volume

Dead Load =10 x 25 = 250 KN/m³

Live Load

Live load is another type of vertical load. It can be defined as the load that is applied on a structure that is not fixed or permanent. It is a movable or moving load without any acceleration or impact. The live load cannot be calculated from the specific formula. Generally, it is assumed for a design. The minimum values of live loads to be assumed are given in IS 875 (part2) – 1987. It depends on the use of the structure.

The following table shows the values of live loads for the following occupancy classification:

• Apartment
• Assembly area
• Resident
• Libraries
• Hospitals
• Recreational area
• Balconies
• Corridors
• Manufacturing
• Office buildings
• Roofs
• Storage area above the ceiling
• Schools
• Stores

S.No	Occupancy	Live Load (KN/m3)	S.No	Occupancy	Live Load (KN/m3)
1	Apartments		7	School
	Office use	2.4		Classroom	1.9
	Computer use	4.8		Corridor above First Floor	3.8
	Armories and Drill Rooms	7.2		First Floor Corridor	4.8
2	Assembly Area			Sidewalks, Vehicular Driveways, and Yards	12
	Lobbies	4.8	8	Stores
	Movable Seats	4.8		First Floor	4.8
	Platforms (Assembly)	4.8		Upper Floor	3.6
	Stage Floors	7.2		Whole Sale, All Floors	6
	Balconies	4.8		Yards and Terrace, Pedestrians	4.8
3	Corridor		9	Residential
	First Floor	4.8		One or Two Family
4	Hospitals			Uninhabitable Attics without Storage	0.5
	Operating Rooms, Laboratories	2.9		Uninhabitable Attics with Storage	1
	Patient Room	1.9		Habitable Attics and Sleeping Area	1.4
	Corridor above First Floor	3.8		Hotel and Multi Families Houses
5	Libraries			Private Rooms and Corridors Serving them	1.9
	Reading Room	2.9		Public Rooms and Corridors Serving them	4.8
	Stake Room	7.2
	Corridor above First Floor	3.8
6	Manufacturing
	Light	6
	Heavy	12
	Marquise and Canopies	3.6

• Garages having trucks and buses should be designed in accordance with an approved method that contains a provision for truck and bus loading.
• In buildings, the room’s height should not be exceeding than 2.3 meters. The nominal shelf depth should not be exceeding than 0.3 meters for each face.
• Live load for railway bridges specified by American Railway Engineering and Maintenance of Association (AREMA) has shown the manual of railway engineering.
• While for highway bridges the live loads are specified by the American Association of state highway and transportation official (AASHTO) in its LRFD bridge design specification.

In multistoried bridges, the live load is directly proportional. The code makes for the reduction of live load in designing structural members like a beam, column, shear wall, slabs, etc. The table shows the reduction of live load In percentage per floor.

No of floors	Reduction in live load in (%)
1	0
2	10
3	20
4	30
5_10	40
over 10	50

Environmental Load

It is a type of vertical load in which the load may act on a structure as a result of topographic or weather conditions. Weather condition means temperature rise at a high level or low. The sudden rise and fall of temperature can also damage the structure.

Snow Load

It is the type of vertical load. The snow which is accumulated on structural member has a tendency to fail the structure or can cause the cracks. Snow loads are present only in snowfall places where snowfall occurs. For example, in hilly areas such as in China, Russia, Europe, Asia, India, and in Pakistan. The IS 875 (part 4) – 1987 deals with snow loads on roofs of the building.

Impact Load

The load applied on structure suddenly is known as impact load. Impact load is dangerous than a uniformly distributed load because the intensity of the impact load is more than a uniformly distributed load. If the value of the impact load is very high, it will directly fail & it won’t even give a chance for the structure to crack.

Horizontal Load

The load applied on structure in a horizontal direction. Horizontal loads are on the x-axis. This load is very effectual because most of the structure is design for vertical force. In this situation, if the horizontal load is applied on structure. The structure will directly fail. The types of horizontal load are given below:

• Wind load
• Earth quick load

Wind Load

The wind load is applied in the horizontal direction on the structure & it is caused by air. Wind load is not effectual for low story building or high rise building maximum up to five stories. These low rise buildings will not get damaged by wind load.

For the designer, the wind load should be kept in mind while designing the building because, for high rise buildings, the wind load is dangerous. It can damage the structure and also can fail the structure.

For calculating the wind load the details of codes are given in IS – 875 (part3) 1987. For designing the wind velocity v₂ this equation must be used:

V₂ = k₁. k₂. k₃. V_b

Where

k₁ = risk coefficient

k₂ = coefficient based on height and structure size

k₃ = Topography factor

Above the 30m height, Wind pressure is increased. To calculating the wind load two components should be kept in mind.

• Velocity of wind
• Size or height of the building

Earthquake Load

Earthquake load is exerted on a structure in both directions i.e. vertical and horizontal direction. The vertical direction is not dangerous for the superstructure of buildings, bridges, dams but the horizontal force is very effectual since both forces are applied at the same time. The structure members can bear the vertical load safely than horizontal force.

The horizontal forces should be kept in mind while designing the structure according to IS 1893 – 2014 that gives the detail of calculating the structures against the earthquake load. There are different zones for earthquake occurrences & the structure’s design depends on these zones. Japan is located in the most dangerous zone. For seismic zone 2 and 3, the building should be less than five stories.

Nowadays every building is design to bear the earthquake loads safely. The design of the earthquake load is totally different from wind loads and gravity. The earthquake has a relatively greater sensitivity to the geometry of structure than wind load and gravity.

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