Introduction of Structural Loads:
Structural analysis is a salient feature of a designÂ of buildings as structural loads can typically cause stress, deformation, and displacement which might result in structural failure.
What Are Structural Loads?
Loads are generally the forces that can cause stresses, deformations, or accelerations. There are an ample range of distinct kinds of structural loads that can act upon a structure. Itâ€™s nature will be discrete according to the design, utilization, location, and materials.
Types of Loads on Structures:
There are two types of Loads on Structures.
Which is as follows.
- Vertical Load.
- Horizontal Load.
1. Vertical Load.-
A load applied in a vertical direction is called a vertical load. They are categorized into the subsequent types:
- Dead Load.
- Live Load.
- Environmental Load.
- Snow Load.
- Impact Load.
1.1. Dead Loads-
Dead loads, also known as static loads, historically referred to a structure’s self-weight or own weight & historically remain constant overtime throughout the structure’s life-span. These loads are additionally termed permanent loads.
Dead loads are additionally referred to as stationary loads. Dead loads may consist of the poundage of any structural components, permanent non-structural segregations, moored attachments like plasterboard, built-in cupboards, etc.
These loads can be enumerated by finding the weights of cubical contents of the miscellaneous materials which are typically being utilized for constructing the structure. Dead loads can be enumerated by estimating the poundage of materials & by additionally estimating their volume.
Material |
Unit Weight of Material |
Plain Cement Concrete [PCC] | 24 kN/m^{3} |
Reinforced Cement Concrete [RCC] | 25 kN/m^{3} |
Steel | 78.5 KN/m^{3} |
Brick Masonry, cement plaster | 20 kN/m^{3} |
Stone Masonry | 24 kN/m^{3} |
Wood | 8 kN/m^{3} |
Floor Finish | 0.6-1.2 kN/m^{3} |
Dead Load Calculation:
Dead loads are usually ascertained by considering the quantity of each & every material and then multiplying it with the unit weight of that particular material. For instance, a column is created of reinforced cement concrete and having a length, breadth, and depth, then the dead load of the column is.
Dead Load = V x d
- V = Indicates the volume of the structure
- dÂ = Indicates the density of the material
Dead Load Calculation Example: Dimension of Column
- Length = 0.4 m (400 mm)
- Breadth = 0.4 m (400 mm)
- Height = 3 m (3000 mm)
Volume of Column Structure = 3.0 mÂ x 0.4 mÂ x 0.4 m = 0.48m^{3}
Here, RCC Strucher Density = 25 kN/m^{3}
Dead Load of ColumnDerived = 0.48 m^{3} x 25 kN/m^{3} >
Dead Load of ColumnDerivedÂ = 12 kn
Dead Load Examples
- Dead Loads on Beam.
- Dead Loads on Slab.
- Dead Loads on Column.
- Walls & Flooring Cover.
1.2. Live Loads-
Live loads, also called super–imposed loads or sudden loads, such as occupants, furniture, or traffic loads, may fluctuate. Live loads changes with respect to time as they depend on usage & capacity.
This type of loading may come and go, hence this is dynamic. An office building may experience surged live loads during week-day work hours but many bijou loads during the night or at weekends. Weight of person. Weight of movable furniture.
Â Types of Floors | Â Minimum Live Loads kN/m^{2} |
Houses, Hospital Wards, Dormitory Floors, Office Floors | 2.0 kN/m^{2} 2.5 kN/m^{2 }& 4.0 kN/m^{2} 2.5 kN/m^{2 }when separate storage facility provided, otherwise 4.0kN/m^{2} |
Shops, Educational Buildings, Assembly Buildings, Restaurants | 4.0 kN/m^{2} |
Banking Halls, Office Entrance Halls | 3.0 kN/m^{2} |
Office Floors for Storage, Assembly Floor Space, Without Seating, Public Rooms in Hotels, Dance Halls, Waiting Halls | 5.0 kN/m^{2} |
Warehouses, Workshops, Factories | Light Wt. Loads- 5.0 kN/m^{2} Medium – 7.5 kN/m^{2} Heavy – 10.0 kN/m^{2} |
Garages | 4.0 kN/m^{2 }to 7.5 kN/m^{2} |
Stairs, Landings, Balconies, and Floor Corridors(not Liable to Over-Crowding) | 3.0kN/m^{2} |
Stairs, Landings, Balconies, and Floor Corridors(not Liable to Over-Crowding) | 5.0 kN/m^{2} |
Flat slabs, sloped roofs | Access Provided – 1.5 kN/m^{2} Access not Provided – 0.75 kN/m^{2} |
1.3. Snow Loads-
This is the vertical load which is generally affected by the deposition of snow and happens more in geographic regions where snowfall is ponderous and frequent.
Consequential or huge quantities of snow can accumulate, adding a considerable load to a structure & that generally has a tendency to fail the structure or cause significant cracks.
The intensity snow load is due to various factors:
- Roof geometry
- Size of the structure
- Insulation of the structure
- Wind frequency
- Snow duration
- Geographical location of the structure
Snow loads are enumerated by the projections made by snow at distinct parts of the structure, e.g., In hilly areas like in China, Russia, Europe, Asia, India, and Pakistan, this kind of load is observed.
Enumeration of Snow Loads on a Structure
The minimum snow load on any area is obtained by the expression:-
S= ÎĽS_{0}
Where,
- S = Design snow load
- ÎĽ = Shape coefficient
- S_{0}Â = Ground snow load.
1.4. Impact Load-
Load applied on a structure abruptly is known as impact load. Impact load is treacherous than a uniformly disseminated load because of the intensity.
The intensity of the impact load is always greater than a homogeneously disseminated load. If the value of the impact load is extremely high, it will directly fail & it wonâ€™t even provide a chance for the structure to crack.
1.5. Environmental Loads-
It is a kind of vertical load in which the load may be affected on a structure as a result of topographic disturbance or tyrannical weather conditions such as temperature rise at a high or low level leading to mutilation.
2. Horizontal Load-
It is typically the load applied on structure in a horizontal direction. Horizontal loads are basically on the x-axis. Usually, when a horizontal load is applied on the structure, the structure will tend to fail or develop some significant cracks.
The categories of horizontal load are given below:
- Wind Load.
- Earthquake Load.
- Thermal Load.
- Settlement Load.
- Imposed Load.
2.1. Wind Loads-
Wind loads are often applied by the drift of air relative to a structure (when the wind is obstructed), & analysis draws upon an understanding of meteorology & aerodynamics.
Wind load usually might not be a major concern for bijou, colossal, low-level buildings, where the dead weight of a structure is insufficient to resist wind loads, but it often procures momentousness with greater apogee, the utilization of lighter materials & also the use of shapes that will affect the flow of air.
Main effects are
- Corner streams or jets often arise around the corners of buildings.
- Vortex shedding frequently arises within the wake of a building.
- Through-flow, or passage-jets, that frequently arise in a passage through a building or bijou gap betwixt two buildings.
Enumeration of Wind Loads on a Structure
- The intensity of wind load depends upon the rate of wind, expansion & aggregate elevation of the building.
- To calculate the aggregate wind load, the subsequent equation is required:-
P_{z}= 0.6 V_{z}^{2}
Where,
P_{z} Is in N/m^{2} at loftiness Z
V_{z} is in m/sec
- Up to the pinnacle of 30 m, the wind pressure is taken into account to act homogeneously. Above 30 m the wind pressure increases notably.
- To enumerate V_{z}Â the subsequent expression is required:-
V_{z} = k_{1}k_{2}k_{3}V_{b}
Where,
- k_{1} = Risk coefficient.
- k_{2} = Coefficient based on height and structure size.
- k_{3} = Topography factor.
2.2. Earthquake Loads-
Significant horizontal loads may be foisted on a structure during an earthquake. Buildings in areas of seismic activity are required to be attentively scanned and designed to corroborate they do not fail if an earthquake occurs.
Earthquake load is exerted on a structure in 2 directions i.e., vertical and horizontal direction. Of late, every building is designed to bear the seismic loads safely.
The design of the earthquake load is in complete contrast from wind loads and gravity. The earthquake features a relatively greater sensitivity to the geometry of structure than wind load and gravity.
2.3. Thermal Loads-
All materials expand or contract with respect to temperature variation, and this may deploy a considerable amount of loads on a structure leading to cracks.
Expansion joints can be provided at points on long sections of structures (wall or floor) in a particular order that elements are physically segregated and may enlarge without any structural defacement.
2.4. Settlement Loads-
Stresses can happen in buildings when one part settles slightly more in comparison to the other. A pliable structure can accommodate bijou stresses, whereas a stiff structure will significantly require careful designs.
2.5. Imposed Loads-
The loads which change continuously are called imposed loads. Few common samples of such loads are the weight of a human, weights of the movable partition, dust loads & weight of the furniture.
These loads were formerly referred to as live loads. In a specific building, the imposed load may be discrete from one room to another room.
Loads may additionally be categorized as:
- Concentrated loads (or point loads): Single loads that act over a comparatively bijou area, such as column loads.
- Line loads: Line loads deploy a load along a line, like a partition’s weight on the floor.
- Distributed (or surface) loads: These exert a load over a surface area, like the weight of floors and roofing materials.
Some other Types of Loads
Some other types of forces or loads are:
- Foundation Movement (IS 1904)
- Erection Load (IS 875- Part2)
- Vibration, Fatigue
- Soil and Fluid Pressures (IS 875- Part5)
- Stress Concentration Effect Due to Point of Application of Load
FAQ: Structural Loads
What are structural loads?
Structural loads refer to forces that cause stress, deformation, or acceleration on a building or structure. These include vertical and horizontal forces that buildings must withstand during their lifespan.
What are the types of vertical loads?
Vertical loads include dead loads (permanent static loads like the weight of the structure itself), live loads (variable loads like occupants and furniture), snow loads (loads from accumulated snow), impact loads (sudden loads like collisions), and environmental loads (loads due to extreme weather or geological factors).
How are dead loads calculated?
Dead loads are calculated by determining the volume of each structural component and multiplying it by the density of the material. For example, for a reinforced concrete column, the volume is multiplied by the density of concrete to obtain the dead load.
What are live loads?
Live loads are transient loads imposed on a structure, such as occupants, movable furniture, or temporary equipment. These loads can vary in magnitude and are not constant over time.
What factors affect snow loads on a structure?
Snow loads depend on factors like roof geometry, insulation, wind frequency, and the geographical location of the structure. Areas with heavy and frequent snowfall experience higher snow loads.
How are wind loads determined?
Wind loads are determined based on factors such as wind speed, building height, shape, and the surrounding terrain. They are calculated using equations that consider these variables to assess the pressure exerted by wind on the structure.
What are earthquake loads?
Earthquake loads are horizontal forces exerted on a structure during seismic events. Buildings in earthquake-prone areas are designed to withstand these loads through specific structural configurations and materials.
How do thermal loads affect structures?
Thermal loads result from expansion and contraction of materials due to temperature changes. These loads can lead to stress and cracking in structures, which is mitigated through the use of expansion joints and appropriate material selection.
What are imposed loads?
Imposed loads are dynamic loads that vary over time, such as the weight of people, movable partitions, or furniture. These loads are considered in structural design to ensure the building can safely support them.
What are the common methods to mitigate settlement loads?
Settlement loads occur when parts of a structure settle unevenly. To mitigate these loads, flexible structural designs or methods such as using pile foundations can be employed to ensure uniform settlement and minimize stress on the structure.