My tower rips itself to pieces?

[Entroper]

It seems if you build lots of cross-pieces in a tower, the entire tower will break instantly upon starting the simulation.  The tower is constructed like this:

At the beginning of the simulation (note that "pause" is activated), the tower looks like this:

Immediately after unpausing, the tower looks like this:

Now, it occured to me, as I'm sure it will occur to many of you, that perhaps the tower is too heavy to support its own weight.  But you would think it would have to "settle" first, and then only the bottom links would be destroyed.  I further studied this by creating a simple box in midair, so that it would freefall toward the ground, and should have no stress whatsoever.  Results:

Perhaps this is some sort of quirk in the physics?  If I were to take a stab in the dark, I'd say that floating point errors are accumulating... I had the same problem in a 3D program I wrote, where a series of rotations screwed up a model's orientation, and really funky things happened to it on the screen.  Maybe if too many beams are putting pressure on each other at once, the same sort of thing happens, and instead of putting insane stretches on a model, it puts those stretches on the beams, causing them to snap almost immediately.

[Gray]

Make screenshots with F8. They are saved in the 'screen' folder. I suggest converting them to jpg before posting. Please also remember to crop it to size so we just see the interesting part (use a graphics program such as Paintshop Pro for this). Resizing to 50% is also good if you're using 800x600 or 1024x768.
Posting only works if you upload the images to some website and link them using IkonCode tags (see the Help pages of this board on how to do this).

(Edited by Gray at 9:34 pm on Oct. 29, 2001)

[baggio]

That's interesting. I hadn't though to build it in the air like that to see what happens. I'm confused now. We've established that short links are weaker. We've also established that you can build a very high, and very strudy tower, built by Calastigro and modified by me.

There are two differences as I see it. Our design doesn't use two long diagnal beams. It features four short beams with a crossbeam joining the front and back -- I added the same pattern to the sides.  Our design also uses a cable to join the top and bottom of the box.

It seems to me, that maybe because the cable allows more stretch, that the cross beams in our design won't break. Check it out:
http://ftp://chronic:logic@24.20.221.2:100/-%20ori....ist.pxb
if you haven't already.

Anyway, I'm late for a review, so I can't delve into this further right now, but if I get the chance, I'll do some more testing.

(Edited by baggio at 8:55 pm on Oct. 28, 2001)

[mikaiser]

I ran into the "exploding sections" problem, too. I could solve it most times by simply changing one "heavy" link against a "light" one. That´s exactly the reason why my tower crane (see "New Levels" thread) is made of mixed heavy and light beams.
The idea of using this effect for "explosive charges" is fun, but without collision detection it would just blow up some air, wouldn´t it?

Ummm, Baggio, just curious....why did you quote his entire post? :-D

[mendel]

You can see Mika's tower (and some exploding discussion) in the General - Tower Building; the New Levels - No Bridges thread he refers to doesn't discuss exploding.

The idea about "explosive charges" is to add some beams to an existing structure to take out some structural supports. If you've ever seen a high-rise demolished (e.g. on TV), you'll notice that the charges doesn't pulverize it all, but rather take out some structural elements so the thing falls down in a controlled manner.

[mendel]

I really like this thread. Although I think the pics entroper uses could've been cropped and he could've put 3 into one (like so and so), that thread is novel, thought-provoking and surprising, and after all, that is what really counts. Thank you! :-)

I have used the slowness of my system to advantage, and have, on low detail so you can see the members betters, made shots of the frames immediately preceeding the collapse for the box and two towers of 80 and 120 meters in height, constructed like entroper's 160m tower.
Xplobox (68kB gif) shows the box right before and after the explosion
XploTwr2 (87kB gif) shows the 4 frames that encompass the demise of the 80m tower
XploTwr3 (84kB gif) shows 4 frames leading up to the downfall of the 120m tower

[Entroper]

If you put in the longest diagonals, it's even funnier looking to watch.  I built a simple 1-unit wide box, putting in every possible diagonal beam everywhere.  When the sim starts, the box is floating in mid-air... and it just pops immediately, throwing the remaining pieces of it in random directions, some up, some down.  It actually had my two roommates and I falling over laughing when we watched it explode on the "fast" setting.  

Anyway, beaujob has created a level with varying tower designs, and it basically verifies that the more beams that intersect at a single point, the worse the 'exploding factor' of the tower.  I'll have him upload it to the Serious Fortress server so you guys can all see what's going on firsthand without having to reconstruct our designs.

[Entroper]

Er, I see his bridge is already uploaded, see the "short-link physics bugs" thread for a link.

[mendel]

Hmmm.... I wonder if these exploding boxes could serve as "demolition chrges" demanded as a new feature for Pontifex on another thread?

Pfx demolition
--------------
Take a given bridge, add members to it (at the least additional cost) so it self-destructs instead of settling :-) The task is completed if all deck pieces are on the ground afterwards; those connected directly to anchors may still be, but must drop down as far as they can go.

Are the explosions the same if you use heavy steel?

[baggio]

As I had theorized in an earlier post, I suspected that the tower I had designed was staying together because of the use of cables holding the tower together. I was wrong.

Subsequent testing has shown that the reason my tower doesn't blowup is because of the "short" diagonal joists. The long ones break. This seems to be in direct contradiction with previous observations.

Additionally, I have been able to increase the number of joints on a story without causing it to blow up, but I have to use short diagonals to do it. Longer diagonals cause stress failure.

Perhaps this is why the small joint boxes don't automatically explode. If they did, it wouldn't make for much of a game.

I'm working on a new tower level right now, to see what other factors are at play, but I have sucessfully built a single column in the entire vertical space without causing any broken links. That is 640m high. It is also the most computationally complex level I've seen yet.  My computer is uncharacteristically slow when testing. I'll make it available when I'm done.

Update: At about ũ.6 million, I ran into the same problem as someone else about their bridge disappearing. I hit the links limit, and consequently wasn't able to build beyond the 5th story. I will try and cut back on some building materials and the design. I know you all are counting on me, but it is late, and I'm going to give up for the evening.

Good luck to everyone who submitted a bridge for the contest, the results come out in T-7:48:23.624...

(Edited by baggio at 5:14 am on Oct. 29, 2001)

[oldie]

Inspired by this tower problem I made my own trials. After several tests I found at least one tower constuction, that behaves nearly like in reality, when it collapses. It destoys itself completly and the biggest remains are only some 1x1 cubes. More than 90 % of the material disappears. If anybody could tell me, how to make a screenshot in pontifex and how to get it posted, I would do it.