# What Is Truss Analysis?

Andrew Kirmayer
Andrew Kirmayer

Often used in bridges, electrical towers, and certain types of roofs, trusses generally consist of bars connected together in a framework. The bar components are typically connected by pins. Truss analysis can be used to determine the compression and tension forces that act throughout the structure. The truss’ structural integrity can be calculated using mathematical formulas and scientific evaluation. In truss engineering, the main methods for analysis often focus on the joints, the sections, or through graphical representation of the structure.

For truss analysis, the rules usually dictate that the bars are connected by pins, and that there is no friction at the joints. It is typically assumed that each component undergoes the same amount of stress along its entire length, while structural loads affect only the joints of the truss. Analysts usually look at the reactions of different forces on the various parts. Truss analysis is typically performed by applying equations of equilibrium.

The method of joints is one way to analyze a truss structure. Generally assuming each piece is in tension, meaning both ends of a bar are subjected to pulling forces, the analysis is performed on a portion of the truss represented on a Free Body Diagram. Two equations are often used for each joint; the number of calculations is double how many joints there are in the structure. Various steps lead to a determination of whether each member is in tension or compression. This approach to truss analysis often involves the use of trigonometric functions for angle measurements as well.

Using the method of sections, the part of the truss design with the most force acting on it is typically needed. Calculations are performed on either side of a dividing line through the truss, relying on equilibrium to guide the calculations. This line can pass through up to three bars on the truss. The tension and compression of each joint is also calculated by this method of truss analysis. Components such as members that do not carry load, ones that transmit forces to the opposite side, and curved parts sometimes need to be considered differently to get the most accurate analysis.

Graphical truss analysis often uses a minimal number of lines by using force polygons. The result can be a simplified drawing called Maxwell’s Diagram, which looks like a triangle on which the forces and angles can be measured. Calculations are usually performed in a clockwise direction around the drawing. Truss analysis is often used to measure the mechanics of such systems before they are built. Complexity of the structure is sometimes a limitation, in which case accounting for the joints in the computations is typically more effective.

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