|
QuickSearch
Welcome! You are not logged in. [ Login ] |
EvC Forum active members: 66 (9028 total) |
| PaulK (1 member, 40 visitors)
|
Michael MD | |
Total: 884,158 Year: 1,804/14,102 Month: 172/624 Week: 56/95 Day: 0/34 Hour: 0/0 |
Thread ▼ Details |
Member (Idle past 234 days) Posts: 20714 From: the other end of the sidewalk Joined: |
Thread Info
|
|
|
Author | Topic: Climate Change Denier comes in from the cold: SCIENCE!!! | ||||||||||||||||||||||||||||||||||||||||||||
Stile Member Posts: 4034 From: Ontario, Canada Joined: Member Rating: 3.6
|
I have a cube of ice.
I let it melt. It makes a puddle. I chill the puddle from the centre... and only half of it re-freezes Yet still, even though I have half the amount of ice, the area covered by the frozen half-puddle is still much larger than the area of the original ice cube. Polar ice caps go through winter and summer cycles. When talking about the amount of ice decreasing... we need to talk about volume, not area. A greater area of ice is consistent with both an ice decrease and an ice increase. Did your source leave out the thickness?
|
||||||||||||||||||||||||||||||||||||||||||||
Stile Member Posts: 4034 From: Ontario, Canada Joined: Member Rating: 3.6 |
I have a few answers, maybe a springboard for more searching?
First, a bit on blocking. First of all, to remove confusion, I believe blocking is not "getting in the way of something" blocking... but more "using a block of wood" to add structural support blocking. Think of framing a wall. When you have a frame, and you put plywood on the outside of it (think of the building of the exterior walls of a house)... I think this is called "shearing" a wall. Plywood comes in 4x8 sheets. However, these sheets are not always long enough to go from base-to-top of a framing wall (think of a 9' ceiling or something like that...). Therefore, you end up with "horizontal joints" in-between the plywood that is not located at the base-2x4 or the top-2x4. This "shearing horizontal joint" is in the middle of the wall... only connecting to the studs. I think the point of the "blocking" is to put in some horizontal support so you can nail in the plywood along these middle-horizontal joints. Now... that's all normal shearing. Normal plywood on a normal frame. Windstorm plywood (again, I think...) is special plywood that is created long enough to go from the base-2x4 to the top-2x4 of the framing without the need of a middle joint. Therefore you don't need need the "blocking" to support the "additional hardware" to support the plywood along the middle-horizontal-seam... because there is no middle-horizontal-seam. The only horizontal seams would be along the already existing base-2x4 and top-2x4. I also found this link helpful: Windstorm FAQ
|
||||||||||||||||||||||||||||||||||||||||||||
Stile Member Posts: 4034 From: Ontario, Canada Joined: Member Rating: 3.6
|
Disclaimer again - not my area of expertise - but here goes with another possible-explanation.
Yes, you are correct if taken literally. However... a wall is not as literally described here. The sheathing (the plywood on the outside) acts just as well as the blocking as far as bracing for lateral movement. In fact, it acts even better because it's larger and connects multiple studs instead of just two specific studs. It also has multiple nails in it per-stud or per-connection... where each blocking only has one point of connection to each stud. To prove this point... think of an Ikea-ish bookshelf. Have you ever put one of these together? However, there's always that super-flimsy back piece you put on those shelves. Put that on... and the entire shelf suddenly becomes super-rigid. This back piece is the sheathing... the plywood we put on an exterior wall. It's very good at preventing lateral movement because it connects the top and bottom and all the studs together into their "full square shape" with multiple connection points (multiple nails per stud or top/bottom piece.) A non-windstorm plywood is good... but if it is jointed in the middle it means it's not connecting the top and bottom and studs all together. It's only connecting the top and studs... or maybe just the bottom and studs. This is "good" but connecting all 4 sides... top, bottom and studs... all together with one large-enough windstorm-plywood (or whatever it's made of) is much better for bracing against lateral movement. Also, there's a step-back view of the whole structure.
Let's go through some pictures: Just need to look at the top-most picture on the right side here. A Truss is one-triangle-piece of a roof support system. Examine the blow-up of the overhang. Understand that the "butt cut" is the part of the roof-truss that is exposed to the exterior wall-side, but not covered by the truss's top chord. I believe a "gable" is a bunch of trusses all together to form a roof. As shown in this picture. The same wind direction is used in the following pictures: We're now looking at the side of the gable... that's why we no longer see the triangle shape. Now with a single piece of sheathing going from bottom of base structure to top of gable: Here, the wind's force is distributed across the entire face of the windstorm sheathing. (The picture doesn't clarify this very well at all - in fact, it makes it seem like it isn't... but it really is - that's just physics.)
I think these questions go back to the first picture again. Remember the "butt cut?" If the butt cut is not covered by plywood, or covered with it's own plywood and not connected to the wall - because the wall-plywood was not large enough - this would make "lift" a difficult problem. It would only be single-point hurricane clips holding the roof to the wall structure. Now, add in windstorm sheathing that goes from the bottom of the wall structure up to the top chord of the roof truss - covering the entire butt cut as well. "Lift force" from the wind still exists - this will always exist as long as the overhang exists. The soffit isn't structural... it doesn't add in to this in any significant way. Any lift force generated because of wind and the overhang (regardless of it going on the soffit or not) will be transferred to the structural connection of the hurricane clips or the windstorm sheathing. The roof will want to come off all together ("rolling") this puts strain on the connection between roof-and-wall/base.
I think this is more of a laymans vs. expert terminology thing. My guess is that nails are technically "hardware" in the sense that you will find them in the hardware section of any hardware store. So I think this is a definitional/contextual confusion issue more than anything else. Maybe if you're talking about "getting nails" you can say you're getting hardware for the job.
This one... I'm really not sure. As far as high winds are concerned... my initial thought is that gaps/seams would help (assuming all other structure aspects are equalized somehow)... because wind blowing through something causes a lot less force than wind getting trapped by something. That why I think this might have something to do with non-hurricane-winds benefits. But maybe it's touching on the idea of more-seams = more-little-pieces-connected-together-instead-of-solid-one-piece-things... which would also imply that the structure is weaker against wind forces (more joints = more possible bending/weakening locations).
|
||||||||||||||||||||||||||||||||||||||||||||
Stile Member Posts: 4034 From: Ontario, Canada Joined: Member Rating: 3.6 |
Absolutely.
I'm not really sure.
I think there are two different problems. The hinge point at the gable-end-frame is one problem. I think we understand that one now, and how windstorm sheathing prevents it. The other problem is the whole lift-issue and danger of rollover. Therefore, the wind would have to change direction from those pictures and come from one of the sides in order to cause this second issue. In my previous post - the section talking about the "butt-cut" and using windstorm sheathing from the bottom-of-the-wall to meet up with the bottom-of-the-top-chord-of-the-roof (covering the "butt-cut") is about protecting these sides and helping to greatly reduce lift along the sides. The windstorm sheathing connects the wall section to the roof section better (apparently) than hurricane clips. I don't really know what a hurricane clip is... but I'm guessing some sort of single-point connector spaced out every 12" or so along the roof-wall connection line. With no windstorm sheathing (and either a narrow piece of plywood covering the butt-cut or nothing covering the butt-cut at all...) these hurricane clips would be the only thing holding the roof onto the wall section. Perhaps there are some nails... but these would be vertical (from the roof down into the wall) - these vertical nails wouldn't do much in stopping the vertical lift from winds. With the windstorm sheathing, we now continue the "flimsy-Ikea-backpiece-greatly-increasing-structural-stability" idea up from the wall section and onto the butt-cut area of the roof section. The horizontal nails holding the windstorm sheathing to the roof butt-cut section would be a great deterrent against vertical lift. As well, there would be many more nails in each windstorm-sheathing piece then there would be hurricane clips (I would guess).
No problem. It was interesting for me too.
|
|
|
Do Nothing Button
Copyright 2001-2018 by EvC Forum, All Rights Reserved
Version 4.0 Beta
Innovative software from Qwixotic © 2021