Product(s):	SACS
Version(s):	ALL
Area:	Collapse

 

Community Question:

Hello Bentley, I'm working on an in-place analysis and I have two scenarios:

• 1.-How is the plasticity ratio defined in SACS? Is it (Von Mises Stress−Fy)/Fy?

Plastic ratio is the ratio of number plastic sub-areas (or integration points) to the total number of the subareas (or integration points) within a given cross-section. 

• 2.-Can we access the following outputs in COLLAPSE for beam members: plastic deformation (or plastic strain), Von Mises stress (or any sort of “equivalent” stress used for the plasticity calculation)?

For plastic deformation (strain), SACS has options that you can select in the card CLPRP inner of your collapse control file; using column 58-59 you can access the different reports of stresses on elements. 

 

• 3.-In the manual, a figure illustrates the definition of “sub areas” for two types of cross sections, stating that “other cross sections are similar”. Could you show the subdivision used for the “Jack up Leg” type of cross section?

We don't have the graphics sub-areas in Standard Collapse. But for Collapse Advanced please see figure 2 in Collapse Advanced user guide for the location of the integration points.

You can activate the report of stresses on integration areas by activating the field shown below.

• 4.-When I run a collapse analysis, no troubleshooting file is generated. How can this be activated?

The troubleshooting file is active only when you run using collapse advance 

• 5.-What does NSLV mean in the collapse history file (first column)?

NSLV is number of solves of linearized system. In a nonlinear analysis, at each iteration, the stiffness matrix is updated and then the program solves the linear system.

• 6.-The collapse simulation takes a long time to run. Do you have any recommendations regarding output writing options that could improve the analysis time?

Sometimes it is a tricky task to improve the time of solving analysis, but in theory you can reduce the time depending on your model. A good recommendation is to set two or three segmentations in all tertiary and secondary elements, while for the interested elements, specify a higher number of segmentations. Normally, SACS considers all modeled beams divided into 8 subsegments along the length for analyzing. You can change these criteria using the next commands, MEMSEG and MEMSEG.

When you face this issue,

It's recommended reviewing the E and Fy on the element with this joint, and if this belongs to a reference structure (dummy) or tertiary structure, and if the result of these doesn't influence the structure collapse, so increase the rigidity on them (diameter and thickness). This is going to avoid the joint will displace and will help us to reach the convergency fast. When we have flexible structures, whit nodes who displace much, usually SACS takes time to reach convergency Most of the cases are linked to the difficulty of reaching the convergence of elements during this type of analysis. We recommend checking this wiki for troubleshooting. 

Reaching convergence In Collapse Analysis

• 7.-I have a very strange geometry in the collapse result animation when using the Jack up Leg section (during the whole simulation, not only at collapse). As shown in the image below, the visualization is correct in “deflected shape”, but very strange during the animation. Is this just a visualization bug? Is there a way to fix it?

If you feel some outcomes from any module of SACS are wrong or could be calculated wrong, please don’t hesitate to send your model for our test and investigation. This way, we can share the files with the developers for their test and clarification. 

here you can find one of the probably reason to have a wrong behavior in Collapse module

Inconsistencies using members with the same joint at the start and end in Collapse Module

• 8.-In the seismic analysis file, in the THLOAD command line, it is possible to select an option to include gap elements in the analysis. This is a dynamic analysis run—how is a nonlinear feature such as a gap element considered in the analysis?

SACS Dynamic Response is a linear time-history solver so we can't directly add nonlinear elements like nonlinear springs into analysis. The way is done is through creating Collapse input and incremental loads using Dynamic Response and then run Collapse (Standard or Advanced) to include any nonlinearity including nonlinear springs