Statics with Autodesk ForceEffect
The Autodesk ForceEffect app, a mobile engineering
app for simulating design concepts in the field or in
the office, brings engineering to the point of the
problem.
Unlike the traditional approach of using paper,
pencil, and a calculator to develop equations for
design options, the ForceEffect app does all the
simulation, design, and engineering calculations for
you right on your mobile device, enabling you to
quickly and easily simulate design options during the
concept phase to determine the viability of a design.
The ForceEffect app determines the forces/moments
in elements (these are called internal
forces/moments or internal loads because they are
inside of the structure) as well as the support
reactions; that is, those forces or moments exerted
by the supports on the structure.
These forces can be sent to experts to determine
whether or not the structure will be safe from the
viewpoint of stress-based failure criteria. Or, the
experts may already have given the ForceEffect app
user the maximum allowable forces/moments for
each element of the structure. In either case, the
ForceEffect app user can alter the configuration of
the structure iteratively in order to design a failureproof structure.
Exercise requirements
These exercises require the ForceEffect app to be
installed. You can use the mobile app as well as the
desktop version.
You can download the ForceEffect app for FREE from
the iTunes app store and Google Play .
In these lessons we will use the Google Chrome
version of ForceEffect. After installing FE you can find
it on the apps tab.
Lessons
 Module One: Introduction to ForceEffect
 Module Two: Manual Analysis Example
 Module Three: Mechanical Example
 Module Four: Chair Example
 Module Five: Structural Example
Module 2: Manual Analysis Example
A traditional manual analysis used to solve a basic
statics problem consists of multiple steps, as shown
in the following pages. In the following section, you
can see how using the ForceEffect app to solve this
same problem makes it much easier and faster...and
you can try it yourself.
Key Principles of Solving a Statics Problem
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The Equilibrium Conditions for a Structure, or a
Free Body Diagram, are:
1. The sum of all (component) Forces in the xdirection is zero,
2. The sum of all (component) Forces in the ydirection is zero, and
3. The sum of all Moments about a point is
zero.
For Equilibrium equations, clockwise Moment
values are positive and counter-clockwise
Moment values are negative.
For Equilibrium equations, component Force
Vector values in the x-direction are positive if
pointing right and negative if pointing left;
similarly, component Force Vector values in the
y-direction are positive if pointing up and
negative if pointing down.
In a Free Body Diagram, the unknown xdirection, y-direction and Moment Force
components are shown as positive direction
Vectors in early diagram renditions until
computations show otherwise. The negative
Force Vector solution values are then adjusted
in the correct directions (left or down or
counter-clockwise, respectively) in subsequent
diagram renditions.
Example Statics Problem
Formulation of the problem:
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Find the Support Reaction Forces at points A and
C.
Find the Internal Loads in Elements AB and BC.
Solution:
Step 1. Drawing a Free Body Diagram
Draw a Free Body Diagram of the entire Structure.
Step 2. Writing Equilibrium Equations
Apply the Equilibrium Conditions on the Free Body
Diagram of Step 1.
∑Fx=0: FCx+FAx=0
∑Fy=0: FAy+FCy+FLoad=0
FAy+FCy+(-100.0 kN)=0
∑MA=0: MLoad+MCx+MCy=0
(100.0 kN)(0.5 m)+(FCx)(1.0 m)-(FCy)(2.0 m)=0
The resulting three (blue) equations must be solved
for the unknowns: FAx, FCx, FAy and FCy.
Step 3. Try to solve the Equilibrium Equations
Evaluate the ability to solve for the four unknowns
with the resulting equations.
Since there are currently only three Equilibrium
equations, but there are four unknowns, the
unknowns cannot be found yet (the same number
of independent equations is required to solve for
the same number of unknowns, e.g., 4 for 4 needed
here).
Thus, another Free Body Diagram is required from
which more equations can be derived by applying
the Equilibrium Conditions again.
Step 4. Drawing a Second Free Body Diagram
Of the two Elements of this Structure, draw a Free
Body Diagram of Element BC, the Element with the
smaller number of Forces (Both elements AB and BC
each have a force at each end. However, element
AB also has Fload. Thus, element BC has fewer forces
acting upon it).
Step 5. Writibg New Equilibrium Equations
Apply the Equilibrium Conditions again on the new
Free Body Diagram of Element BC.
∑Fx=0: FCx+FBx=0
∑Fy=0: FCy+FBy=0
∑MB=0: MCx+MCy=0
(FCx)(1.0 m)-(FCy)(1.0 m)=0
Thus: FCx=-FBx, FCy=-FBy and FCx=FCy.
The last of these three above resulting equations
(blue) can be combined with the previous three
equations (blue) in Step 2 to solve the four
unknowns: FAx, FCx, FAy and FCy.
Step 6. Solving the Combined Set of Equations
Now solve the set of four Equilibrium equations
(blue) simultaneously for the unknown Forces: FAx,
FAy, FCx and FCy.
FCx+FAx=0
FAy+FCy+(-100.0 kN)=0
(100.0 kN)(0.5 m)+(FCx)(1.0 m)-(FCy)(2.0 m)=0
FCx=FCy
Solving for these four Forces:
FAx=-50.0 kN, FAy=50.0 kN, FCx=50.0 kN, FCy=50.0 kN
Step 7. Showing Support Reaction Components
These four Forces (FAx, FAy, FCx and FCy) are the x and
y components respectively of the single Support
Reaction Forces at the Fixed Pin Support points A and
C.
Step 8. Finding Single-Force Support Reactions
Compute the single Support Reactions at points A
and C from the x and y component Forces: FAx, FAy,
FCx and FCy.
Solving for these two Forces:
FRA = (FAx)(cos135˚)+(FAy)(sin135˚)
= (-50.0 kN)(cos135˚)+(50.0 kN)(sin135˚)
= 70.7 kN @ 135˚
FRC = (FCx)(cos45˚)+(FCy)(sin45˚)
= (50.0 kN)(cos45˚)+(50.0 kN)(sin45˚) =
=70.7 kN @ 45˚
Step 9. Showing Single-Force Support Reactions
Show the resulting Support Reactions on the Free
Body Diagram of the entire Structure.
Step 10. Showing Internal Loads in Element BC
Show the Internal Loads on the Element BC in a
Free Body Diagram.
Step 11. Showing Internal Loads in Element AB
Show the Internal Loads on the Element AB in a
Free Body Diagram.
The previous statics problem was solved manually.
The next section shows the method for solving the
same problem by using the ForceEffect app.
Solving the same problem with ForceEffect
As you will see, after simply diagramming the
problem properly, the ForceEffect app automatically
performs much of tedious, laborious manual
computation work.
1. Start New Diagram at Home Page.
2. Drop the image of exercise from DataSet to
canvas.
3. Use
(the Element icon) to create elements
AB and BC.
4. Use
(the Construction Line icon) to create
construction lines between points B and C.
5. Open Settings and select Metric units.
6.
Use
(the Scale icon) from AB element
context menu to set the scale of your diagram
(enter 1 m). Make sure that the AB element is 1
m in length.
7. Set the length of both Construction Lines to 1 m.
8. Use
(the Force icon) to specify a force in
your diagram (element AB). Set the Magnitude
of force to 100 kN.
9. Use
(the Select icon) to select the force and
edit its dimensions to 0.5 m as on the screen.
10. Use
(the Fixed Pin icon) to create a fixed
pin supports at points A and C. The reactions will
be shown automatically. If you have another
reaction, check the angles and length of the
diagram elements.
11. Click the Report button to look at the results
report.
Through the ForceEffect app’s Report function,
you can also see that the background equations,
diagrams, and computations are still visible as
they would be if the work were done manually.
12. Try to iterate free body diagrams to find
construction options with reaction forces less
than 55 kN (the distance between points A and C
should be fixed – 2 m, the Force should be
applied at the middle of the AB-element).