CE 201 - Statics

Chapter 6 – Lecture 19

STRUCTURAL ANALYSIS

The main objective of chapter 6 is to use the equilibrium equations to analyze structures which are composed of pin-connected members.

This is a simple structure composed of three pin-connected members AB, BC and AC.

It is assumed that as long as the structure is in equilibrium, then all members are in equilibrium.

Forces at the joints (A, B, and C) can be found by applying equilibrium equations at different parts of the structure.

�A

C

B

Simple Trusses

E D

CB

A

Joint B

Members are joined together by bolting or welding to a common plate (called guset plate)

Planar Trusses

Planar trusses lie in one plane ( i.e x-y plane). Forces acting on the joints and they lie in the same plane as the truss. That is why this type of trusses is considered as a two-dimensional truss.

Assumptions for Design

To design a truss, it is necessary to find the force that will develop in each member at certain loading conditions. To do that, the following two assumptions are made:

All loadings are applied at the joints Weight of members is neglected If weight is to be considered, then it has to be divided

equally at both ends The members are joined together by smooth pins If welding or bolting to a common plate was used, then the

center lines of connecting members must be concurrent

Assumptions for Design

Assumptions for Design

Each truss member acts as a two-force member If the force tends to elongate the member, then it is a tensile force (T) If the force tends to shorten the member, then it is a compressive

force (C)

Compression

Tension

Simple Truss

Simple truss is constructed by starting with a basic triangular element such as the ABC truss below.

C

B

A