[Jai Khullar]

I'm using ansys v14.5 to simulate the progressive collapse of a 3 storey structure with 2 bays in x direction and 2 bays in y direction(if seen along z direction).

Materials: Conc-35Mpa(RHT strength model) and steel with piece wise JC model.

My model consists of line bodies and solid bodies of which line bodies are used to model 12 mm circular diameter reinforcements for columns and beams of with assignment of steel whereas solid bodies are used to model .5m x .5m columns with height of 4m and beams .5m x .5m spanning 6m(in both x and y directions). Slab thickness is .3m and stirrups in columns and beams are at 300 mm spaced apart with reinforcement contact function.

I have used design modeler to create the model and exported it to the ansys explicit dynamics solver module. There I have defined the following conditions:

1. Fixed support : to the bottom of the column faces.
2. Standard acceleration due to gravity.

To model progressive collapse I have removed the central column from the ground storey by suppressing the bodies and transported my model from explicit dynamics to autodyn.

I have given the run time of 10ms.

The problem I now face is the analysis taking never ending time.

Can someone suggest me a way out? Will parallel processing help in this case? Also any additional info for this will be highly appreciated.

Please feel free to ask if any info is needed.

Below is the image of my model in mechanical(explicit dynamics) for the reference.

[siw]

The timestep in explicit dynamics simulations is determined from the size of smallest cell, so you may need to improve your mesh for this type of simulation. Using 1-D or 2-D bodies can help simplify things. Meshing requirements are stricter in explicit dynamics than implicit FEA, e.g. use hexahedral cells rather than tetrahedral cells. You must have full control over the mesh, do not use any automatic meshing.

Alternatively, you can use mass scaling to increase the mass of said smallest elements to increase the solver timestep. You set a minimum timestep and the solver adds the mass to the cells to reach the timestep. Run for a few timesteps and check on the locations and quantity of added mass. But it is better to improve the mesh than add mass.

You are using v17.1 so read the dedicated explicit dynamics analysis guide in the Help as it covers this.

[Jai Khullar]

Thank You Siw, I'm really sorry for my late reply I will try what you have suggested.

I will incorporate the changes of solid elements into line bodies and surface bodies.

Are you implying that the generation of mesh in ansys should be avoided and I should manually give the element size for each of my components?

One more thing, I conducted a simple analysis of a 4 pillar frame (sub unit of the building) with beams and removed one of the columns for a time run of 1000ms with mass scaling. This run took almost a day.

I noticed in my analysis -

the eroded bodies which are detached from the parent body should fall in under the influence of the gravity(boundary condition for whole model in -ve Z direction) while the structure should deform slowly during the time run. But this is not so as the eroded appears to fall at the same rate at which the structure is distorted. The image below is a reference to what I am trying to convey. I don't know where I'm going wrong?

I've also heard that LS dyna will be feasible for such type of analysis. Is it so? I'm bit of confused right now. Any suggestion would help. Should I stick to Autodyn or shift my focus to LS Dyna?

Thanks!!!

[siw]

With regards to the first point, I am saying you should have full control over the mesh rather than let ANSYS make any auto meshing. So it is recommended to set your own element sizings and avoid letting ANSYS make any auto meshing. Again I refer you to the Help Guide and Training Material.

I do not use LD-DYNA or AUTODYN, instead I use the Explicit Dynamics analysis system in Workbench; which uses the AUTODYN Lagrangian solver, so I cannot comment on LS-DYNA.