Engineering is the broad branch of science that investigates and analyzes the use of systems, structures, and forces; structural engineering is a subset of this discipline that focuses on the design and support capability of these structures to withstand internal and external forces (load). Axial force evaluates the internal forces that exist in a structure, often presented by the characteristics of its dimensions. For example, picture a bisectional view of a door knob fastened to a door and designate the transition of dimension as three segments: the length of the tip of the handle to its base, the length between the base of the handle and the edge of the mounting frame, and the length between the edge of the mounting frame to the intersection with the door. Each of these segments bears a load that supports the assembly when in use.

Identify the components. Axial force is determined by width, effective length, and load and is measured in kilo pounds or kips (1,000 pounds of force). Using the aforementioned door example, define the components as handle to base (ab), base to mounting frame (bc) and frame to door (cd).

Identify the formula. A general formula for axial force is Ned equals 270 times KN, where E equals 7,000 times MPA, KN equals 1,000 times Newton and d equals 640.3 times mm. Assume the segments farthest from the door interception are positive due to centrifugal force and that which is closet is negative. Use effective segment lengths of 40, 50 and 10 for segments AB, BC, and CD. Compute axial force for AB as –FAB minus (40 kips upper plus 40 kips lower) plus 50 kips plus 10, which equals -20 kips, BC as – FBC plus 50 kips plus 10 kips, which equals 60 kips, and CD as –FCD plus 10 kips, which equals 10 kips.

Use an axial load calculator. Draw the axial force diagram (free-hand) taking note of each point where a transition occurs and labeling and measuring this section in inches. Then convert the inches to meters and enter the components for diameter, coils and deflection in the calculator and solve for axial force. Websites such as Engineers Edge, Futek and Engineering Toolbox offer several options for calculating axial force in structures.

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