# What is a structure ?

A structure means a system of connected parts used to support a load. An elastic body is called a structure when a set of loads are applied the elastic body deforms and also the system is set up against the deformation. If no resistance is set up in the structure in return to the applied loads it is known as an unstable structure or mechanism.

## Classification of structure

### Skeletal structure

Structures that can be idealized to a series of straight or curved lines. Ex: Roof trusses, building frames.

### Surface structures

We can idealize structures which to plane or curved surfaces. Ex: Slabs and shells.

### Solid structures

It is not possible to idealize structures to a skeleton nor to a plane or curved surface. Ex: Massive foundation.

## Classification of skeletal structures

### Based on type of joint

• Pin jointed frames: Members connect by means of pin joints. These frames support the loads by developing only axial forces if the external loads’ act at the joints and members are straight.
• Rigid jointed frames: These frames resist external forces by developing bending moments, shear forces, axial forces and twisting moments in the members of the frame.

### Based on dimensions

• Plane frames: All members of the plane frame, as well as the external loads, is to be in one plane.
• Space frames: All members do not lie in one plane. Very often, it is also a combination of a series of frames.