---
title: "Axial Force Diagrams | Intro to Civil Engineering"
description: "Axial force diagrams show how axial force changes along a beam, column, or frame member, helping you spot tension, compression, and load effects."
canonical: "https://fiveable.me/introduction-civil-engineering/key-terms/axial-force-diagrams"
type: "key-term"
subject: "Intro to Civil Engineering"
unit: "Unit 7"
---

# Axial Force Diagrams | Intro to Civil Engineering

## Definition

Axial force diagrams graph the internal axial force along a structural member in Intro to Civil Engineering. They show where a member is in tension or compression and how that force changes from point to point.

## What It Is

Axial force diagrams are graphs that show the internal force acting along the length of a structural member in Intro to Civil Engineering. The force is measured along the member’s axis, so the diagram tells you whether the member is being stretched in tension or squeezed in compression.

In practice, you build the diagram after finding the support reactions and then cutting the member at different locations to see the internal axial force. That means the diagram is not a load drawing, it is a force response drawing. If the member carries only end loads, the axial force diagram may stay constant over long sections. If loads are applied at several points, the diagram changes in steps at those load locations.

The sign convention matters. Many classes use positive axial force for tension and negative axial force for compression, but you should always follow the convention given in your notes or textbook. A positive value means the member is being pulled apart along its axis, while a negative value means it is being shortened by axial compression.

These diagrams show up most clearly in beams, columns, and frames. A beam under mostly vertical loading may have little axial force, while a column in a frame often carries strong compression. In a truss or a braced frame, some members may switch between tension and compression depending on the load path.

To read one well, look for jumps, flat regions, and sign changes. A jump usually means a point load or concentrated axial force was added or removed. A flat segment means the axial force stays the same between those points. If the diagram crosses zero, the member changes from tension to compression or the other way around.

## Why It Matters

Axial force diagrams are one of the quickest ways to see how a structure is carrying load before you size a member or check for failure. In Intro to Civil Engineering, they connect equilibrium equations to real structural behavior, so you can trace how an external load turns into internal tension or compression.

That matters because different members fail in different ways. A steel tie may be fine in tension but unsafe in compression. A column can carry compression, but too much of it can lead to buckling. When you read the diagram correctly, you can match the internal force pattern to the right design check.

They also help you compare load paths in beams, columns, and frames. A beam might mainly show bending and shear, while a column in a frame may show a strong axial force pattern. In a frame analysis problem, the axial force diagram can reveal which members are taking the direct push or pull from the applied loads.

The skill is useful on problem sets, lab reports, and sketch-based questions because you often need to explain not just the number, but where it comes from. If you can point to the region of tension or compression on the diagram, you are already describing the structure the way an engineer does.

## Connections

### Equilibrium

You use equilibrium equations first to find the support reactions and internal forces that feed the axial force diagram. Without balancing forces in the free-body diagram, the diagram is just a guess. In class problems, equilibrium is usually the step that turns a structure picture into numbers you can plot.

### [Beam](/introduction-civil-engineering/key-terms/beam)

Beams often carry mostly transverse loads, so their main diagrams are usually shear force and bending moment, not axial force. Still, a beam can have axial force if it is part of a frame or if the load acts along its length. That makes the axial force diagram a useful check for combined behavior.

### Shear Force Diagram

A shear force diagram tracks internal force perpendicular to the member, while an axial force diagram tracks force along the member. They are often read together because they describe different parts of the same loading problem. If you mix them up, you can assign the wrong stress state to a section.

### Bending Moment

Bending moment measures the tendency of a member to curve, while axial force measures push or pull along its axis. A member can have one, the other, or both at the same time. Comparing the two diagrams helps you see whether the structure is acting more like a stretched or compressed member, or a flexing one.

## On the AP Exam

A quiz or problem-set question may give you a loaded beam or frame and ask you to sketch the axial force diagram from the support reactions. You will usually set a sign convention, make section cuts, and mark where the force changes because of point loads or member connections. If the structure is part of a frame, you may also need to identify which members are in tension and which are in compression. Another common move is interpreting a finished diagram and explaining what the flat sections, jumps, or zero crossings mean physically.

## axial force diagrams vs Shear Force Diagram

Shear force diagrams show internal force perpendicular to the member’s axis, while axial force diagrams show internal force along the axis. If the load is vertical on a beam, the shear diagram is often the first one you look at, but an axial force diagram tells you whether the member is also being pulled or pushed lengthwise. They answer different structural questions.

## Key Takeaways

- Axial force diagrams show internal force along a member, so they tell you where a beam, column, or frame element is in tension or compression.
- You usually build the diagram after solving reactions and making section cuts, because the plot comes from equilibrium, not from the original load sketch.
- Flat segments mean the axial force stays constant, and jumps usually happen where a point load or concentrated force is applied.
- The sign convention matters, but the physical idea is simple: positive often means tension and negative often means compression.
- In civil engineering, the diagram helps you decide whether a member is likely to fail by stretching, crushing, or buckling.

## FAQs

### What is axial force diagrams in Intro to Civil Engineering?

Axial force diagrams are graphs that show how the internal force along a structural member changes from one point to another. In Intro to Civil Engineering, they are used to see whether a beam, column, or frame member is in tension or compression. The diagram comes from equilibrium and section analysis, not from the external load picture alone.

### How do you draw an axial force diagram?

Start by finding the support reactions, then cut the member at the points where the axial loading changes. Solve the internal force in each segment using equilibrium, and plot the result with your sign convention. Point loads create jumps, while segments with no added axial load stay flat.

### How is an axial force diagram different from a shear force diagram?

An axial force diagram tracks force along the axis of the member, while a shear force diagram tracks force perpendicular to it. For a beam under vertical loading, shear is usually more obvious, but a frame member may have both. The two diagrams describe different internal effects and should not be swapped.

### What do tension and compression mean on an axial force diagram?

Tension means the member is being pulled apart along its length, and compression means it is being pushed together. Many classes label tension as positive and compression as negative, but you should follow the convention your instructor uses. The sign tells you the type of internal stress the member is carrying.

## Related Study Guides

- [7.3 Beams, Columns, and Frames](/introduction-civil-engineering/unit-7/beams-columns-frames/study-guide/RFGM1pXOVVZNAItW)

## About This Document

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