engineering core courses

Statics
Course homepage
Statics
Course homepage
C3: Structures
3.1 Introduction to Plane Trusses
- Theory - Two-force members
3.2 Method of Joints
- Theory - Example - Question 1 - Question 2 - Question 3
3.3 Method of Sections
- Theory - Example - Question 1 - Question 2 - Question 3
3.4 Frames and Machines
- Theory - Example - Question 1 - Question 2

C3.1 Introduction to Plane Trusses

Introduction

Ever notice those triangular network of metal frames when you drive past a bridge or walk under a roof?


Example of a roof truss and bridge truss; schematic of a truss in Statics

C3.1 Introduction to Plane Trusses

Introduction

Ever notice those triangular network of metal frames when you drive past a bridge or walk under a roof?


Example of a roof truss and bridge truss; schematic of a truss in Statics

These are what we call trusses, and they play an extremely important role in ensuring the stability of structures. As such, analysing and designing such structures is important for all you budding engineers.

Plane trusses

In this Statics course we will only be considering 2D trusses of plane-trusses. In trusses, we essentially have many individual truss members connected at joints.

Each truss member can be assumed to be two-force members, with only normal forces acting internally within each member without any bending moment. These internal forces can be treated as forces exerted by the truss members, acting from the tips:

Two-force member assumption in trusses, with forces acting from the truss member's tips

The two-force member assumption is not made randomly, but can actually be proven to be valid. We show you the proof here.

Statically determinate

If you were tasked to design a truss structure, how would you check whether the number of truss members in your design is insufficient (causing the truss to collapse) or excessive (resulting in overdesign)?

There is a simply formula to check this:

Formula to check for static determinancy of a truss

Consider the following truss configurations that illustrate the scenarios of being statically determinate or indeterminate:

Example of a statically determinate and statically indeterminate truss

Observations:

  • when m+3 > 2j, there are more members than necessary, and this represents an overdesign
  • when m+3 < 2j, there are less members than necessary, and the structure will collapse

Okay! That’s probably enough background information on trusses. Let’s move on to analysing them, starting with the method of joints.

These are what we call trusses, and they play an extremely important role in ensuring the stability of structures. As such, analysing and designing such structures is important for all you budding engineers.

Plane trusses

In this Statics course we will only be considering 2D trusses of plane-trusses. In trusses, we essentially have many individual truss members connected at joints.

Each truss member can be assumed to be two-force members, with only normal forces acting internally within each member without any bending moment. These internal forces can be treated as forces exerted by the truss members, acting from the tips:

Two-force member assumption in trusses, with forces acting from the truss member's tips

The two-force member assumption is not made randomly, but can actually be proven to be valid. We show you the proof here.

Statically determinate

If you were tasked to design a truss structure, how would you check whether the number of truss members in your design is insufficient (causing the truss to collapse) or excessive (resulting in overdesign)?

There is a simply formula to check this:

Formula to check for static determinancy of a truss

Consider the following truss configurations that illustrate the scenarios of being statically determinate or indeterminate:

Example of a statically determinate and statically indeterminate truss

Observations:

  • when m+3 > 2j, there are more members than necessary, and this represents an overdesign
  • when m+3 < 2j, there are less members than necessary, and the structure will collapse

Okay! That’s probably enough background information on trusses. Let’s move on to analysing them, starting with the method of joints.

engineering core courses

COURSES FEATURES THE STORY CONTACT US ECC facebook link
engineering core courses