Introduction:
A truss is a structural framework consisting of straight members connected at their ends by joints. Trusses are commonly used in engineering and construction to support roofs, bridges, and other structures. There are different types of trusses based on their configuration and how they are formed. One type of truss is formed by joining two or more simple trusses, and this type is called a compound truss.

Explanation:
A compound truss is formed by combining two or more simple trusses. It is created by connecting the joints of the simple trusses together. The members of the simple trusses become the members of the compound truss. The purpose of joining these simple trusses is to create a larger and more complex structure that can support greater loads and spans.

Key Points:
Here are some key points to understand the concept of a compound truss:

1. Simple Trusses: Simple trusses are basic truss structures consisting of triangular elements. They are made up of straight members connected at their ends by joints. Simple trusses are statically determinate, meaning the forces in all the members can be calculated using equilibrium equations.

2. Compound Trusses: A compound truss is formed by combining two or more simple trusses. The joints of the simple trusses are connected together to form the compound truss. The members of the simple trusses become the members of the compound truss. Compound trusses are used when the span or load requirements exceed the capabilities of a single simple truss.

3. Increased Strength and Stability: By joining simple trusses together, a compound truss provides increased strength and stability compared to a single simple truss. The additional members and connections in the compound truss distribute the loads more effectively, reducing the stress on individual members.

4. Versatility: Compound trusses can be designed in various configurations to suit different structural requirements. The arrangement and combination of simple trusses can be customized based on factors such as span length, load capacity, and aesthetic considerations.

5. Structural Analysis: The analysis of a compound truss involves determining the internal forces in each member, such as axial forces and bending moments. This analysis is usually performed using structural analysis software or by applying the principles of statics and equilibrium.

Conclusion:
A compound truss is formed by joining two or more simple trusses together. It provides increased strength, stability, and versatility compared to a single simple truss. Compound trusses are commonly used in engineering and construction to support larger spans and heavier loads.