A stable, resistant and rigid structure

Structural analysis and conditions

From time to time something goes wrong with a design and a structure collapses to do its job. There are many causes of structural failure and these can include: poor design, fatigue and the failure of a material, an component  or a joint. Failure occurs because of loads acting on the structure.

A structure which will not topple over easily when acted upon by a load is said to be stable. To gain a better understanding of stability, it's necessary to understand center of gravity.

The position of a structure's center of gravity has a lot to do with stability. When a stable structure is tilted, its center of gravity rises. This is very important because when the tilting force is removed, gravity pulls the structure back to its original position. When an unstable structure is tilted however, its center of gravity moves downwards. If the center of gravity moves outside the base area, gravity will make the structure topple over.

Some general rules about structural stability: the lowest the center of gravity, the more difficult it is to make a structure topple over, therefore the more stable is the structure. It is more difficult to make a structure with a wide base topple over so, the wider the base therefore, the more stable the structure.

The shape and the material used to built a structure determine its resistance. Resistance is the capacity of a structure to bear the tensions that it is subjected to without breaking. It depends on material used to build the structure, and the shape of the structure. All materials have a breaking stress, which is the maximum force per unit of surface area that they can bear without breaking.

The shape of the structure determine its rigidity. Rigidity also comes from triangulation and welding joints. To design a polygon-shape structure that can be deformed we use triangulation. This means that all polygons formed by the bars must be based on the triangle. This is called bracing and it prevents square frames from being deformed.

Watch and check out this video about what makes bridges so strong with Triangulation as an important condition, click on the image below: