Input to Program Truss 2D

Some examples

Presently the program is configured to analyze trusses which have less than 80 members, less than 40 joints , and less than 20 different support forces.

Do NOT calculate support forces and enter them as known forces, the program will (and must) do that for you.

In order to make changes or to enter additional data into a particular box move the mouse cursor to the desired spot and click. A blinking vertical bar will appear which you can move within an existing line with the arrow keys. Data are entered or deleted (Del key) where the blinking vertical bar appears.
Changes to all Fill-In Boxes can be made in arbitrary order until of course the "Calculate Forces .." button is hit.

You may use the "Back" button of your browser to return to this document and will find all entries in the boxes still intact. You may then apply changes to the entries for another round .....

Joints and Members
For each joint use a single line to enter :
The label of the joint followed by the x- , and y-coordinate of its location.

You also have to provide the units in which you measure the coordinates if you like to have this program determine the weight of the members of your structure.
Choose from the menu :

For each member use a single line to enter :
The labels of the two joints at either end of the member separated by at least one blank.

External Forces
Select your units for the forces from the menu :
Distribute your external forces between the two options below whichever way is easiest for you, but you can list it only once and there can be only a single external force per joint.

For each external (load or support) force which will not be specified elsewhere but for which you have some knowledge about its components give on a single line the following information :
a) the label of the joint on which the force is acting
b) an indicator for each of the two components of the force in the order x y. If a particular component is unknown, type the corresponding axis label. If a component is known, type the value including sign (+ -).
Example 1 : A x y is a force acting on joint A. Its x- and y-component are unknown.
Example 2 : K 0 y is a force acting on joint K. The force is pointing along the y-axis with unknown value.
Example 3 : B x 0 is a force acting on joint B with unknown x-, and 0 y-component
Example 4 : C 100 200 is a force acting on joint C having the values 100, 200 for its x-, y--component, respectively.

For each external force ( load or support) which will not be specified elsewhere but for which you have knowledge about a line along which it is acting enter a single line containing the following information :
a) the label of the joint the force is acting on
b) a vector (all three components separated by blanks) pointing along the direction the force is pointing. The magnitude of the vector is arbitrary.
Example 1 : A 0 1 is a force acting on joint A whose line of action is parallel to a line pointing from the origin of your coordinate system 0 units in the +x direction, 1 unit in the +y direction.

The following entries are optional. If the box "Tensile stress limit" is empty, all other boxes below will be ignored and the determination of cross-sections and mass of truss members will be suppressed.

Enter the Tensile stress limit in your members :

Enter the Compressive stress limit in your members :

and choose units :

Actually, nobody wants to live on the verge of breakage , so we need a certain safety factor :
This safety factor will be applied towards buckling as well as compression and tension.

As you may know, members under compression can also fail due to buckling, see Chapter 9.2. In addition to the length of a member this phenomena is also governed by details of its cross-section and a certain property, the modulus of Elasticity E, characteristic for the material the members are made out of.

Give modulus of Elasticity : and choose units :

In order to calculate the mass , we need the density of material : and choose units :

For each member the program will determine the characteristics of its cross-section. For members under tension this simply means to determine the diameter assuming circular cross-section. For members under compression the compressive stress limit as well as buckling are taken into account.

Zig Herzog,
Last revised: 02/21/07