Rigid Sim RnD - Reinforced Building Destruction

[SanJuan]

Hello all! I was hoping to get some help with a personal project of mine.

TLDR: How to break solid geometry intersected by bending geometry?

It's a relatively simple sim of a building destruction that I've done before - I'm using Steven Knipping's Applied Houdini Rigids II and III as a starting point. That said, I want the structure as a whole to be networked by rebar to reinforce it all so that the pieces keep together as the building collapses, rather than crumbling into a pile of rubble.

The building is fairly simple itself: it's a floor, four walls with windows, columns and a center spine, and I can control the amount of floors I want.

The rebar structure is a lot more complicated, but it's essentially a series of tubes and circles swept onto splines procedurally scaled and copied into place.

So here was my intention: boolean the building to fit the rebar inside it, prefracture the building into voronoi pieces, apply a glue constraint onto the concrete and a bend constraint on the metal, then have whatever force destroy the object. The boolean method is proving to be pretty taxing on my machine, and it's turning up mistakes in the pieces. If I use a boolean before fracturing my object, I get random polygons intersecting the "holes" that should fit the rebar. If I boolean the object after it's been fractured, I somehow end up losing several pieces (on top of the fact that it'll take several minutes for the operation to apply. Either way, sometimes the boolean will subtract the wrong piece by mistake.

I'm not entirely sold on using the boolean or the prefracture method, I just went for those because they're the most familiar to me. Essentially, I just want the pieces to keep together realistically as they break. Here's an example of what I'm going for: https://vimeo.com/105993048#t=10s

To recap, here are the questions I'm left with at the moment:

• If I use the prefrac + boolean method, how do I go about having a clean boolean with the network of thin tubes I'm working with?
• If I don't use this method, is there a more efficient way to have the pieces stick to the rebar network?

I'm also concerned that the way I've built the rebar out of instanced cylinders might be inefficient, or unnecessarily heavy. Therefore:

• Is there an alternative method of weaving this reinforcement (perhaps using splines) that'll still look like rebar and still interact with the broken pieces properly?

I appreciate any and all feedback. I'm relatively new to Houdini, so this whole project'll serve as a substantial learning experience.If you know of any tutorials out there or any reference videos that are similar to what I'm trying to do, please feel free to point me to them.

[Solitude]

Typically you wouldn't actually attempt to simulate the actual rebar -- you would use the existing constraint types AS rebar. You want to make it look like it's being held together by rebar by using a combo of friction - springs - conetwist - whatever... then add rebar geometry in later, as a visual, by just attaching it to the rbds.  Getting the geometry clean enough to be all convex hulls would be incredibly hard to do automatically, and likley very slow with some kind of convex decomposition tool. Also, simming as concave geo is likely to be extremely slow and unstable. 

[SanJuan]

That's true, I hadn't considered the awkward sim hulls I would get from the boolean. So that way's probably out.

I think I'll be able to get the pieces to break and stick right through trial and error, but I'm gonna have to do some research on constraint types first. As it stands, I've mostly been using glue and hard constraints so far.

Now what about the rebar geometry then? I'm not too sure about how to attach it to the rbds. If I start with tubes, how should I make them flex and break with the pieces? If they're independent of the actual simulation, my concern is that they'll look like straight bars clipping through the geometry.

Edited October 16, 2017 by SanJuan