In building construction and structural engineering, understanding the loads acting on buildings is important. A load refers to any force or weight acting on a building, and recognizing these loads is crucial for designing safe and resilient structures.
Various types of loads, such as dead loads, live loads, wind loads, and seismic loads, exert different pressures on buildings and influence their structural integrity. This introduction provides an overview of the loads encountered in building design, their characteristics, and the importance of considering them in the construction process to ensure the durability and safety of buildings.
What Is Structural Load?
Structural loads in buildings produce various types of activities such as deformations, stresses, or displacements. Structural loads are an important factor in the design of buildings.
Different load act on a structure such as vertical load (dead load, Live load), horizontal load (earthquake load, wind load), longitudinal load, etc.
The main reason behind the failure of any structure is that load-carrying capacity is low as compared to the actual load applied to the structure. The structural load may be Compression, Tension, and Shear in nature.
Types of Load
The following are different types of loads,
1. Dead load
(Note: IS CODE 875- 1987 (PART 1) code covers unit weight or mass of the various types of materials and various components in a building and that apply to the determination of dead loads in the design of buildings or Structures.
What Is a Dead Load?
A dead load is a stationary or permanent load. This dead load transferred the load to the structure throughout the life span of the structure. Dead load is acting due to the self-weight of structural members, fixed permanent equipment or Furniture, permanent unit.
Unit Weight of Building Materials:
| Sr. No | Name of material | Weight of material |
| 1. | Brick Masonry | 18.8 KN/m^3 |
| 2. | Timber | 5.8 KN/m^3 |
| 3. | Stone Masonry | 20.4 – 26.5 KN/m^3 |
| 4. | Plain Cement Concrete (PCC) | 24 KN/m^3 |
| 5. | Reinforced Cement Concrete (RCC) | 24 KN/m^3 |
Assessment of Dead Load
The following factors affect the calculation of dead load on the structure,
- Self-weight of the member or structure.
- Weight of various materials in the construction.
- Weight of permanent Member or Structure.
- Weight of fixed service equipment and furniture.
- The net effect of pre-stressing.
2. Imposed loads or Live Load
(Note: IS CODE 875- 1987 (PART 2) code covers imposed loads or live loads to be assumed in the design of buildings. Generally imposed loads are minimum loads that should be taken into consideration for the purpose of structural safety of buildings.)
What Is Imposed Load?
The live load is assumed to be produced by the occupancy of a building, which includes the weight of movable members, concentrated loads, distributed loads, vibration, load due to impact, and dust load.
But it does not include the earthquake load, seismic load, wind load, snow load, and other loads due to changes in temperature, differential settlement, shrinkage, etc.
Occupancy or Grouping
The main aim of occupancy is building used for various purposes. That group is described below,
- Assembly Buildings – An assembly building shall include any building or part of a building where groups of people gather for recreation, amusement, social programming, religious function, travel land many more, for example, assembly halls, theatres, city halls, etc.
- Business Buildings – Business buildings shall include any building or part of a building, which is used for the transaction of business for the keeping records of accounts and similar purposes; offices, banks, courthouses, and library, etc.
- Educational Buildings – These shall include any building used for school, college, classic for education or recreation, etc.
- Industrial Buildings – These shall include any building or a part of a building like factories, plants, power plants, refineries, gas plants, etc.
- Institutional Buildings – These shall include any building or a part thereof, which is used for purposes, such as medical or other treatment in case of persons suffering from physical and mental illness, disease, or infirmity; care of infants, It includes hospitals.
- Mercantile Buildings -These shall include any building or a part of a building that is used as shops, superstores, markets either wholesale or retail, etc.
- Residential Buildings – These shall include any buildings in which cooking, bathing, and dining facilities include .for example dwellings, apartments, Rowhouse, etc.
- Imposed loads are acting on the floors due to occupancy and use
Floors shall be investigated for both the concentrated load and uniformly distributed load specified in Table.
NOTE 1–In case no values are given in the tables for concentrated load or point load it means assumed distributed load is sufficient for analysis purposes.
NOTE 2 – The loads are given in the table uniformly distributed loads on the plan area and they do not take into consideration special concentrated loads and other loads.
NOTE 3 – Where the use of floor area is not provided in Table the imposed load due to the use and occupancy of such an area shall be determined from the analysis of loads resulting from:
1. Assumed Weight of persons in the assembly
2. Approx weight of the equipment and furnishing;
3. Approx weight of storage materials
4. Impact factor
Imposed Floor Load For Different Occupancies
| Sr.No. | Occupancy Classification | Uniformly Distributed Load | Concentrated Load / Point Load |
| 1. | Residential Building | ||
| All Room and Kitchen | 2 KN/m3 | 1.8 kN | |
| Toilet and Bathroom | 2KN/m3 | – | |
| Passage, Staircase, and Store Room | 3 KN/m3 | 4.5 KN | |
| Balconies | 3 KN/m3 | 1.5 / m PL at the outer edge | |
| Living Room, BedRoom | 2 KN/m3 | 1.8 KN | |
| Kitchen and Laundries | 3 KN/m3 | 4.5 KN | |
| Public Lounges | 3 KN/m3 | 2.7 KN | |
| Store Room | 5 KN/m3 | 4.5 KN | |
| Dining Room | 4 KN/m3 | 2.7 KN | |
| Office Room | 2.5KN/m3 | 2.7KN | |
| Room for Indoor Game | 3 KN/m3 | 1.8 KN | |
| Bath and Toilet | 2 KN/m3 | – | |
| 2. | Educational Building | ||
| Offices and Staff Room | 2.5KN/m3 | 2.7KN | |
| Projection Room | 5 KN/m3 | – | |
| Kitchen | 3KN/m3 | 4.5KN | |
| Toilet and Bath Room | 2KN/m3 | – | |
| Store Room | 5 KN/m3 | 4.5KN | |
| Reading Room | 3KN/m3 | 4.5 KN |
Load Application
The uniformly distributed loads given in the above table shall be used as static load over the entire area of the floor under consideration and the portion of the floor area whichever produces a critical effect on the structural members which is provided in design codes.
The design of floor-At which place point loads are applied is a critical portion of the floor because we need to calculate the shear and bending moment for avoiding deflection.
Where the calculation of punching and crushing at that time is assumed to be over an actual area of the analysis is 0.3 X 0.3.
Imposed Loads on Various Types of Roofs
On sloping roofs, flat roofs, and curved roofs where imposed loads are applied on the floor level due to the use of the buildings and the geometry of the roofs. Which is given below
| Sr.No. | Types of Roof | UDL Imposed load on Plan area |
| 1. | Flat, sloping, or curved roof with slopes up to and including 10 degrees | |
| A. | Access provided | 1.5 kN/m^2 |
| B | Access not provided | 0.75 kN/m2 |
| 2 | sloping roof with slopes greater than 10 degrees | purlins-0.75 kN/m^2less 0.02 kN/m’ |
Point Load or Concentrated Load acting on the Roof
All roof covering materials other than glass or transparent made of fiberglass shall be capable of carrying a load of 0.90 kN concentrated on an area of 12.5 cm2.
Loads Due to Rain
In the rainy season, the accumulation of rainwater in the drainage system affects the imposed load on the roof. Dust Load – In prone areas such as steel plants and cement plants, dust spreads everywhere on the surface of the roof. Find out the accumulation of dust for the used dust load equivalent.
3. Snow loads
The amount of snow load on a roof structure is dependent on various factors
- Geometry of roof
- Shape and size of the structure
- Insulation of the structure
- Frequency of wind
- Duration of snow
- The geographical location of the structure.
4. Impact Load
Impact load is produced by the vibration or impact or acceleration in the structure. So imposed loads or live loads are equal to the impact loads. Imposed load incrementing with the percentage is known as impact or impact factor. The impact factor depends on the impact intensity.
5. Earthquake Load (Seismic load)
DIFFERENT IS CODE USED FOR EARTHQUAKE LOAD
IS CODE 1893-2002 ( PART-1 ) General provision for building
IS CODE 4326- 1993
General Principal for construction of the earthquake-resisting building
1. Lightness:
Since the earthquake force is a function of mass, the building shall be as light as possible consistent with structural safety and functional requirements. Roofs and upper stories of buildings, in particular, should be designed as light as possible.
2. Building Configuration:
The building should have a simple rectangular plan and be symmetrical both with respect to mass and rigidity so that the centers of mass and rigidity of the building coincide with each other in which case no separation sections other than expansion joints are necessary.
Buildings having plans with shapes like L, T, E, and Y shall preferably be separated into rectangular parts by providing separation sections at appropriate places.
3. Strength in Various Directions:
The structure shall be designed to have adequate strength against earthquake effects along both horizontal axes. The design shall also be safe considering the reversible nature of Earthquake forces.
4. Ductility:
The main structural elements and their connection shall be designed to have a ductile failure. This will enable the structure to absorb energy during earthquakes to avoid the sudden collapse of the structure. Providing reinforcing steel in masonry at critical sections, as provided in this standard will not only increase strength and stability but also ductility.
5. Damage to Non-structural Parts:
Details shall be worked out to connect the non-structural parts with the structural framing so that the deformation of the structural frame leads to minimizing damage to the non-structural elements.
6. Scope: Earthquake-resistant design of buildings. Its basic provisions are applicable to buildings such as elevated structures, industrial, stack structures, bridges, concrete masonry, earth dams, embankments, retaining walls, and other structures.
A temporary component like scaffolding and temporary excavation does not need to design with earthquake forces.
The seismic zone 2, and 3 without more than 5 stories are made up of monolithic reinforced concrete.
5. Wind loads
(Note: IS CODE 875 – 1987 (Part -3) code gives wind forces and their effects in nature of static and dynamic that are used in designing the buildings, structures, and components of their Buildings.)
In wind load, the main consideration is the comfort of people inside and outside of the buildings.
Wind loads are initially horizontal in nature because of the movement of air relative to the earth. Wind load is required to be considered in design especially when the building exceeds two times the transverse dimensions to the exposed wind surface.
The following steps are used for wind load design.
Design Wind Speed ( Vz ) – The basic wind speed ( Vz) for any site shall be obtained from the map.
a) Risk level
b) Terrain roughness, height, and size of the structure; and
c) Local topography.
Basic wind speed is expressed as follows
Vz = Vb XK1 X K2 X K3
Vb = design wind speed at any height
K1 = Probability Factor
K2 = Height, Terrain category, and Structure size
K3 = Topography Factor
Basic wind speed is expressed as follows
Design wind pressure
Pz = 0.6 X Vz^2
Pz = Design wind pressure in N/m^2 at height z
Vz – Design wind velocity in m/S at height Z
Wind Load on Individual Member
F = ( Cpe – Cpi) X A X Pd
Cpe = external pressure coefficient,
Cpi = internal pressure- coefficient,
A = surface area of a structural or cladding unit
Pd = design wind pressure.
The amount of wind load depends upon the following factors
- Geographical location
- Size of the building or structure
- Type of surrounding environment
- The shape of the structure
- Height of the structure
6. Accidental Load
General -The occurrence of accidental load with significant value is unlikely on a given structure over the period of time under consideration and also in most cases is of short duration.
The accidental loads are generated out of human action which is given below,
- Collision impacts
- Fire
- Explosion
The above loads are not easy to avoid. They required extensive effort.
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