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Old 01-15-2018, 06:52 AM   #1
wmervine4
 
Join Date: Dec 2013
Location: Noblesville, Indiana, USA
Default [Magic] Earth to Air in a stone tower

This past weekend I ran another session of my home brew fantasy campaign (inspired by and including material from DF and ToG 3e). During a battle in a stone tower, the timely use of the Earth to Air spell (standard Magic) has left me with some questions about the consequences of this action.

For a slight bit of background, the adventurers are currently in an old one-story fort that is mostly rectangular in shape, but features a three story tower in one corner. The fort is constructed entirely of gray stone and is built with quality masonry that has survived for several centuries.

Before entering the tower, the group employed Sense Life to detect that there were 9 adversaries inside. They all went in and one of the group charged up the ladder to the second floor encountering 8 foes waiting for her (the 9th is presently unaccounted for). For a time during the rest of the battle, there was some concern about how to get the rest of the party up to the second floor to assist her. Several people used the ladder which took a few seconds, but one guy had a different idea. Rather than waiting his turn to ascend the ladder, the martial artist/ritual air mage of the group decided to use Earth to Air to punch a hole in the ceiling (the floor for those on the second story).

This is where I'm wondering what could/should "realistically" happen. The tower is 30' (10 yards) in diameter with thick stone walls and stone floors. The only natural opening in the floor on each level is a 3' x 3' square against the wall where an iron ladder is attached leading up to the next floor. This new opening is on the floor of the second floor (ceiling of the first floor) one hex (3') away towards the center of the room from the natural opening for the ladder that leads up from the first floor to the second. Stated another way, there is an open hex against the wall where the ladder comes up, then moving towards the center of the room, there is a hex of stone floor that is still intact, and then the open hex that was Earth to Aired.

We were substantially over our allotted time for the game, so I ended the session at the end of the battle during which the spell was cast, so a few seconds have passed since the actual casting. Using some rough math, I figure the 8 adversaries on the second floor and 5 PCs/NPCs with all their equipment total about 3,500 lbs.

My main question is, would this use of Earth to Air compromise the structural integrity of the tower causing a collapse? If so, how long would this take? Seconds? Minutes? Would there be a way to avert this disaster?

I recognize that from a story perspective I could just hand wave this issue entirely and let the group move on as though nothing had happened, but I would like to impose even a smidgen of a reality check on this scenario rather than blatantly ignoring something that seems to me like a potential catastrophe.

Last edited by wmervine4; 01-15-2018 at 06:54 AM. Reason: Updating title to put book reference in brackets per "standards" (in other words, what I've seen other people typically do).
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Old 01-15-2018, 07:08 AM   #2
VariousRen
 
Join Date: Apr 2015
Default Re: [Magic] Earth to Air in a stone tower

So the actual math for figuring out what's going to happen is beyond me, but I can give a few insights from low level structural engineering classes I took early in my degree.

Stone is strong in compression, but it's hard to find mortar that's any good under tension. If you just had a floor made of stone bricks with mortar between them, it would almost certainly fall apart under it's own weight with any serious span. More likely, the stone tower either had:

1) a shallow dome (arch in rotation) that supported the 2nd story floor, which would be visible from the 1st story. This turns the tensile stress on the mortar into compression stress on the actual stone. Removing part of the dome would be a bad idea, the floor should be heavily compromised. Note that even if the floor collapses the walls of the tower will remain standing, and the upper floors will be fine.

2) A wooden framework that supported the floors on each floor. Looking up from floor 1 you would probably see a grid of wooden beams (maybe covered in iron, if you were worried about people taking the bottom of the tower and hacking at them from below). When stone to air was cast the stone would have been removed but the wooden supports would remain. The floor should be fine, as long as no fool goes around and hacks up these support beams too.
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Old 01-15-2018, 08:37 AM   #3
malloyd
 
Join Date: Jun 2006
Default Re: [Magic] Earth to Air in a stone tower

Quote:
Originally Posted by wmervine4 View Post
My main question is, would this use of Earth to Air compromise the structural integrity of the tower causing a collapse? If so, how long would this take? Seconds? Minutes? Would there be a way to avert this disaster?
The tower itself should be fine, the stresses causing it to stand up should be carried in the walls, not the intermediate floors. This is generally true, putting holes big enough for humans to fit through in the wall of anything really ought to require an Architecture roll to not bring part of the structure down and fill said hole and the surrounding area with rubble.

The ceiling/floor that has been compromised might come down - timescale on that could be seconds (or less) - but since that amounts to the party mostly dies (and the enemies on the upper floor may have a reasonable shot at survival even if they are in a self sacrificing mood) you probably don't want to do that.

If you want to discourage this sort of exploit in the future, you can go with some local weakening - have just a bit of the surrounding structure collapse on the caster immediately, inflicting a die or two of damage, and the floor give way under anybody who enters a hex adjacent to the hole (dropping them out of the fight for a while and inflicting the 1 story falling damage, and widening the danger zone) from there on out.
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Old 01-15-2018, 09:41 AM   #4
wmervine4
 
Join Date: Dec 2013
Location: Noblesville, Indiana, USA
Default Re: [Magic] Earth to Air in a stone tower

Quote:
Originally Posted by VariousRen View Post
1) a shallow dome (arch in rotation) that supported the 2nd story floor, which would be visible from the 1st story. This turns the tensile stress on the mortar into compression stress on the actual stone. Removing part of the dome would be a bad idea, the floor should be heavily compromised. Note that even if the floor collapses the walls of the tower will remain standing, and the upper floors will be fine.
I like this answer. Having the floor collapse while the rest of the structure remains standing is a good narrative consequence, and will inject a bit of fear to both halves of the party (those on the first floor from the stones falling towards their heads and those on the second floor from the stones suddenly failing to support them). Thank you for this!

Quote:
Originally Posted by malloyd View Post
The tower itself should be fine, the stresses causing it to stand up should be carried in the walls, not the intermediate floors. This is generally true, putting holes big enough for humans to fit through in the wall of anything really ought to require an Architecture roll to not bring part of the structure down and fill said hole and the surrounding area with rubble.
Funny story, the half-elf leading the charge up the ladder to the second floor has Architecture, but she failed her roll when asked by the ritual air mage if disintegrating part of the floor/ceiling would be okay, to which I responded, "You're quite sure it will be fine." I feel like proceeding with this course of action was appropriate given the failed roll to discern that something might go amiss.

Quote:
Originally Posted by malloyd View Post
The ceiling/floor that has been compromised might come down - timescale on that could be seconds (or less) - but since that amounts to the party mostly dies (and the enemies on the upper floor may have a reasonable shot at survival even if they are in a self sacrificing mood) you probably don't want to do that.
Agreed. TPK is not what I'm going for here, but I feel like some consequences are warranted.

Quote:
Originally Posted by malloyd View Post
If you want to discourage this sort of exploit in the future, you can go with some local weakening - have just a bit of the surrounding structure collapse on the caster immediately, inflicting a die or two of damage, and the floor give way under anybody who enters a hex adjacent to the hole (dropping them out of the fight for a while and inflicting the 1 story falling damage, and widening the danger zone) from there on out.
This is a good idea for future applications of this spell in precarious situations like this. I appreciate the suggestion!
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Old 01-15-2018, 02:15 PM   #5
Anaraxes
 
Join Date: Sep 2007
Default Re: [Magic] Earth to Air in a stone tower

Medieval stone towers generally had wooden floors. Sometimes the lowest floor would be stone, supported by arches in the basement below. If there was no basement, then the floor would be earth, or stone sitting on the earth underneath. Occasionally you'd have a flagstone upper floor supported by wooden beams. But structural stone on the interior floors was rare, especially for upper stories. The necessary arches take up too much space on the floor beneath.

The roof of a tower was most often thatch. Slate supported by wooden beams appeared sometimes as well.

So, assuming that 2nd floor was stone, you mostly likely have some missing flagstones, but would still have the wooden beams. (Probably spanning the 1-yard hole; as I recall from kitchen remodeling, modern rules for granite countertop overhangs keep them under ten inches for 3 cm thick stone.) No structural issues, as the rest of the floor is still supported by the beams.
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