Live loads: examples, concept and characteristics
We explain Live loads with concept, characteristics and examples. The live loads that act on a construction are those of a temporary nature and that also change in magnitude and location. They originate according to the use that is given to the structure and include people who come and go, cars, elevators, machinery of all kinds, furniture and even natural events such as the pushing of water and land, among others. live load examples
In civil engineering and construction, the set of forces acting on a certain structure is called “load”. They are specified in units of force, such as kilogram-force (kg), newton (N), or pound-force (lb), but are more often expressed in terms of force per unit length or area: kg / m , kg / m 2 .
In the latter case, they are used for large structures such as slabs, while force / length units are preferable when length is the most relevant magnitude, such is the case of handrails.
Live load concept
The concept of live load becomes clear when we think about the number of people who circulate through a large shopping center and compare it with those who circulate through a low-rise residential building. live load examples
The mall is expected to host many more people than a residential building, so its live load is higher.
This is one of the main factors that builders must take into account, since everyone inside the structure must be safe.
For this reason, when designing the construction, engineers consider these events and thus estimate the load that the building must withstand. Loads are the forces received by the structure, consequently, builders select the type of construction and the most appropriate materials to carry it out. live load examples
The load produced by people, vehicles and others is due to their weight , since the Earth’s gravitational field exerts its influence on all objects near its surface and is translated into a force directed vertically downwards.
Live load characteristics
-They arise from the use of the building.
-They are not permanent.
-They originate in people, who are in constant movement, and in objects.
-Your location can be changed.
-Its magnitude is variable, even going so far as to cancel out.
-They do not include environmental loads, that is, those due to wind and weather. live load examples
Uniform and concentrated live loads
To facilitate calculations, many building codes consider live loads to be divided into:
Building floors are subject to uniform loads , specified in kilograms per square meter or other appropriate unit of force per square meter. In the next section you will find numerical examples of the most frequent ones. live load examples
On the other hand, the concentrated loads are, for example, automobiles or other types of machinery. Uniform, concentrated live loads are found in construction such as parking lots.
How to calculate live loads?
Builders do not know the exact number of people who will go to a mall on a given day, so they use statistical methods to estimate how many are circulating at most on a busy day, say just before Christmas.
They also judge that a sudden overload occurs, because the probability of it happening, even if it is small, must be taken into account. This gives a margin of protection.
There are building codes in each country, which indicate the minimum live loads for a certain structure, according to the use to which it is intended. These values are determined by statistical studies carried out on existing structures.
For safety, the engineers check that the structure supports loads greater than the minimum, since there are other loads that can act unexpectedly, caused by factors such as the action of nature, for example. live load examples
Once all loads are considered, including dead or permanent loads, live loads, and loads due to other factors, such as wind, snow, and ground and water pressure, the engineer uses software to set the parameters. design.
Live load reduction in large areas
In some structures a reduction of the minimum live loads is allowed, as long as the surface is large. This is because the estimated live load is unlikely to occur simultaneously throughout the building.
Live loads during construction live load examples
During the construction of a work it is also necessary to consider live loads, which include machinery, such as cranes, construction materials, tools and personnel working.
Minimum values of live loads
As we have said, the estimate of the live load depends on the purpose of the construction. In addition, in the same building, the live load can vary according to the environment. For example, in an office building, the live load is expected to be higher in common areas than in a given room.
There are tables with the most frequent live loads and their minimum values. The examples mentioned below allow the reader to get an idea of the forces per unit area that are handled in each case: live load examples
Homes, hotels and residences
In general, the live load that is handled in private residences is, on average, 180 kg / m 2 or 1.92 kN / m 2 . Hotels have slightly higher loads of up to 200 kg / m 2 (1.96 kN / m 2 ).
Corridors and common areas have even higher loads: 4.79 kN / m 2 . live load examples
Schools, universities and reading rooms
The loads are similar to those in hotels: 200 kg / m 2 (1.96 kN / m 2 ), but the corridors above the ground floor carry loads of 3.83 kN / m 2 (391 kg / m 2 ).
Book deposits live load examples
They are subjected to higher loads than the previous structures, since they are estimated at 5 kN / m 2 (510 kg / m 2 ).
Hospitals live load examples
Rooms are calculated like hotels: up to 200 kg / m 2 (1.96 kN / m 2 ), but the minimum live load in operating rooms is double: 400 kg / m 2 (3.92 kN / m 2 ).
Railings and handrails
In this case, they are designed to resist 0.75 kN for each linear meter.
Stadiums live load examples
Stairs must be built to withstand 400 kg / m 2 (3.92 kN / m 2 ), while ladders support 5 kN / m 2 (510 kg / m 2 ).
Car parks also carry 5 kN / m 2 (510 kg / m 2 ) as estimated live load. live load examples