Consider the first challenge shown below.
You are asked to support the load (arrow shown in red) by dragging and dropping structural members between the grid points shown. Members can be no longer than 5 grid points in length. The brown regions can be used for structural supports. Members must not cross or touch the grey regions (representing for example non-structural soil). All members are assumed to be made of the same cross section. Continue adding members until you think that you have created a structure that can support the loading specified.
Suppose that your structure now looks like the one below.
Clicking on Start to test the structure.
The structure deflects at zero loading.
Looking at the deflected shape shows us that the bay to the left of the load has changed from a rectangle into a distorted parellelogram. This suggests that we add a bracing member in this bay as follows
Click on start and the loading on the structure begins to increase. Clicking on Pause at a loading of 65 units shows the situation is as follows
The numbers display represent the loadings in the individual members, a positive number indicating a member in tension. Press Continue to resume the simulation. The loading continues to increment until the first member reaches its maximum load (100 units)
This structure is now on the point of collapse and the loading cannot be increased. The maximum loading in a member is assumed to be 100 units whether it is loaded in tension or compression. This assumes that all members have a very low slenderness.
Some structures can continue to support loading after failure of one or more members (redundant structures). In this case each member is assumed to carry its maximum load of 100 units and the loading is increase until the next member reaches failure. In these case considerable extra load can sometimes be carried after failure of the first member (See the example on the opening page of this site).
For loadbearing structures the program will calculate the required structural weight. The object is (of course) to design a structure requiring the lowest possible weight. For the purpose of calculating the structural weight only the loading on the structure to the failure of the first member is considered. The required weight is then equal to the amout of material required when the loadings reach 100 units.