This menu is related to processes requiring a numerical calculation:
- Form finding
This opens the window of iterative process for nonlinear calculation of the structure.
The tensile structures analyzed with WinTess3 accept loads on the nodes and on the surface of the membrane. To be able to enter loads on the surface of the membrane, it is necessary that there are elements. If there is no any element, the program will warn us if we select surface loads and we generate them through the menu Elements | Automatic generation. There are different types of surface loads:
- wind loads
- snow loads
- internal pressure (only pneumatic structures).
- prestress loads
From version 3,117 , WinTess introduces a new way to apply the safety factors to the structures.
NOTE: Although this method is much more versatile and is better suited to the modern normative, if preferred, the user can ignore it and continue to calculate as it was before the version 3,117.
Window of safety factors is seen above. The coefficients are grouped in two columns:
It is an escalating coefficient. That is to say that the loads are multiplied by this value. By default the value is 1, so that if you do not change, the calculation is done as always.
On the other hand, if this value is changed, it must be borne in mind that results (reactions, displacements, etc. ) will be affected by this value.
If you are analyzing what standards or codes define as SLS (Serviceability Limit State), these coefficients tend to be all equal to 1.
It’s a reduction coefficient., i.e. the resistance of the materials are divided by this value. By default, these values are the same as, what WinTess3, until version 3.117, regarded as typical values (membrane = 5, tube = 1.65, cables = 3).
Apply default values
By this button, all the boxes of the safety factors are filled with the default values entered in the options window.
If you are analyzing what the standards or codes define as ULS (Ultimate Limit State), the program multiplies the values of the safety factors of the loads and materials by obtaining a Global Safety factor for that object, and uses this value for the calculation of the ratio of all the objects in the structure: membrane, cables, pipes, …
Update unbalanced forces
The program always evaluates the unbalanced forces of the structure during the calculation process. In fact it does not stop the iterative process until the imbalance is practically non-existent. Now, at a given moment, if we want to know the state of balance of the structure, especially if we have made some kind of edit, we can use this menu to force an update of these unbalanced forces.
Cp manual (Wind)
The program prepares itself to assign wind coefficient Cp to different elements.
If we select an element or group of elements (through a window) and then click the right button of the mouse, we get:
In this window, we assign Cp value to the selected elements. We must be careful to give a positive value for suction and a negative value for pressure loads.
The program prepares itselt to assign snow coefficient Cn to different elements. The default value of Cn is 1.
This value is used to multiply the snow load in certain areas of the membrane, which may be different:
1) In areas that are highly exposed to wind, Cn may be < 1 2) In low areas where it is possible to accumulate snow, Cn can be > 1
We select an element or a group of elements (through a window) and then press the right mouse button, we get:
In this window, we assign the Cn value to the selected elements.
We can visualize Cn values of each element at any time by using the Cn button on the right column.
Form finding (global)
This menu initiates the process of form finding by the Force Density Method. This method is a linear process of solving a system of equations where the coordinates of the nodes are unknown. For the balance it is assumed that each bar has a tension equal to its length multiplied by a factor or “density“.
If we touch the button in the Form Finding state, this menu is run. If the number of nodes is not very high, this process is very fast. However, if the number of nodes exceed certain values, the process slows down quite a bit, and if the number of nodes is too high, it could even crash the program. For this reason, there is another method to find the form what we call “step by step” and discussed below.
Form finding (step by step)
This menu initiates the process of form finding by the Step by Step method. This method is an iterative process in which a node is resolved each time. Its coordinates take the value obtained by the Force Density method applied only on this node.
Once all the nodes are modified, it returns to the start of the process. This repetition is done as many times as needed until the maximum displacement of any node in the iteration is very small.
This process is much slower than the method of global or Force Density, but it has the advantage that the program doesn’t lock even if the number of nodes is very high.
Form finding (automatic)
This menu does not execute any action but it activates or deactivates a change sensor. During the state of Form finding, if this change sensor is activated, whenever you modify the data of a node or a bar, the program automatically finds the new form.
This is very comfortable for structures of few nodes, since we now don’t have to click on button on the menu to find new forms. However, for structures with many nodes, this can be annoying since finding the process could take a long time, and we don’t always want to find a new form on having modified data. Usually we modify various data and then find the form.
If the sensor is activated, the menu presents check mark to the side of the menu.
Especially in the state of Analysis, it is good to know the results obtained. WinTess3 can display a large number of tables with the results in nodes, bars, cables, tubes, etc. However these tables can be very long and of little interest.
This is why the most interesting results are grouped in a combined table of results. We can get this table using this menu, and also using the button on the left called “Output”.