Analysis of Statically DETERMINATE TRUSSES

1. Classify each of the trusses

in the figure below as stable,

unstable, statically determinate,

or statically indeterminate. The

trusses are subjected to

arbitrary external loadings that

are assumed to be known and

can act anywhere on the

trusses.

Problem Set 5

2. Classify each of the trusses

in the figure below as stable,

unstable, statically determinate,

or statically indeterminate. The

trusses are subjected to

arbitrary external loadings that

are assumed to be known and

can act anywhere on the

trusses.

Problem Set 5

METHOD OF JOINTS

In the method of joints, the axial forces in the members of a

statically determinate truss are determined by considering the

equilibrium of its joints.

1. Always assume the unknown member forces acting on the joint’s

free-body diagram to be in tension (i.e. pulling on the pin). If this is

done, then numerical solution of the equilibrium equations will

yield positive scalars for members in tension and negative scalars for

members in compression. Once an unknown member force is found,

use its correct magnitude and sense (T or C) on subsequent joint

free-body diagrams.

2. The correct sense of direction of an unknown member force can,

in many cases, be determined by inspection.

METHOD OF JOINTS

METHOD OF JOINTS

METHOD OF JOINTS

Identification of Zero-Force Members

1. If only two noncollinear members are connected to a joint

that has no external loads or reactions applied to it, then the

force in both members is zero.

2. If three members, two of which are collinear, are connected

to a joint that has no external loads or reactions applied to it,

then the force in the member that is not collinear is zero.

METHOD OF SECTIONS

The method of sections involves cutting the truss into two

portions by passing an imaginary section through the members

whose forces are desired. Sections should be chosen that do

not pass through more than three members with unknown

forces. The desired members forces are then determined by

considering the equilibrium of one of the two portions of the

truss.

METHOD OF SECTIONS

METHOD OF SECTIONS

1. Using the method of joints, indicate all the members of the

truss shown in the figure below that have zero force.

Problem Set 6

2. Determine all the member forces and identify zero-force

members. Use method of sections to double-check the force in

members CD, ID, and IH.

Problem Set 6

3. Determine the force in members GF and GD of the truss

shown in the figure below. State whether the members are in

tension or in compression. The reactions at the supports have

been calculated.

Problem Set 6

4. Determine the force in members BC and MC of the K-truss

shown in the figure below. State whether the members are in

tension or in compression. The reactions at the supports have

been calculated.

Problem Set 6

5. Determine the force in members HG, JC, and BC of the

compound truss shown in the figure below. The reactions at the

supports have been calculated.

Problem Set 6