Loads-Analysis of Structures-Part-1

I will explain what the loads are and how they are used in the structural analysis. In this article you will find answers to questions like what do you mean by structural loads, what are the different types of structural loads, etc. People with limited engineering knowledge and engineering students will get most benefit from this article.

Depending on type of loads applied on a support structure and arrangement of its structural support, a set of internal forces develops inside the support structure. In order to find these internal forces and support reactions at its supports a structural analysis of a structure is required.

Point Load: Point load is a concentrated load that acts on a particular place. Point loads are denoted with an arrow and its magnitude. If a beam supports other small beams the total loads coming from the small beams are point loads. Similarly, if a beam supports a column, the total load coming from the column is a point load.

Uniformly Distributed Load (UDL): Uniformly distributed load has a constant magnitude of load per unit length along the support. For example, weight of a rod which is 1 kg per metre run (1 kg/m). Similarly, weight of a beam per meter run, etc. UDL is calculated for a certain cross sectional area of a support structure such as a beam. If a brick wall is supported by a beam, the weight of the wall is a UDL.

Area Load: Area loads are similar to UDL but spreads in two directions. For example, number of people on a floor standing close to each other. Area loads are expressed as force per unit area. For example 250 kg per square meter, i.e. 250 kg/m2.

During structural analysis a structure is simplified and represented by a line. Self weight of the support structure is added to its overall loading. For example, the beam is represented by a line. Weight of the beam is added separately to the point load.

Following figures show an actual and simplified beam structure. The simplified structure contains UDL to represent the self weight of the beam.

In order to represent a slab a similar structure like beam is used but area load is converted to a UDL by considering a certain strip of width.

Other uniformly distributed loads are also represented by a UDL, for example, imposed live load, such as, human and its belongings, weight of flooring, etc. Similarly, other common loads include series of point loads, varying loads, etc. Following figures show some examples of different types of common loads. Determination of total loads and centre of gravity are dealt in the article Determination of Support Reactions. 

In addition to these loads various other loads are also possible such as Moments, and Torsions, etc. In some places instead of direct loads we also load the structures with indirect loads such as deformation, temperature, etc. 

Related reading: Terminology of Structural Analysis, Centre of gravity of triangularly varying force

In the next article I will be discussing about Structural Supports