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Old 04-10-2009, 11:40 PM   #16
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Wildcat, your assesment may make work on paper, but when have you ever seen deflection in a masonry wall above grade? I really think the discussion here is about above grade, unless the OP is going to side under ground.
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Old 04-10-2009, 11:59 PM   #17
 
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I've seen many above grade masonry walls where deflection had a serious negative impact. They were under reinforced, or the proper grout was not used to connect the masonry units to the reinforcement, or proper waterproofing was not used. Both of these cases lead to deflection and cracking that resulted in moisture intrusion. Moisture intrusion caused all kinds of issues like spawling, severe efflorescence, corrosion of reinforcement, etc. In most of the cases the walls were barely reinforced to take wind load, so there is no way they where going to be able to support axial load for roof or floor above as well as act as a shear wall.
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Old 04-11-2009, 12:13 AM   #18
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I still beg to differ Wildcat. Unless your talking about commercial walls that may be 30 or 40' high. I've seen a ton of residential above grade walls 8-10' high with NO re-enforcement that would outperform any wood wall when it comes to deflection. And just remember, the more load you put on a masonry wall (in perspective to width) the stronger the wall becomes.
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Old 04-11-2009, 12:33 AM   #19
 
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Quote:
Originally Posted by jomama45 View Post
I still beg to differ Wildcat. Unless your talking about commercial walls that may be 30 or 40' high. I've seen a ton of residential above grade walls 8-10' high with NO re-enforcement that would outperform any wood wall when it comes to deflection. And just remember, the more load you put on a masonry wall (in perspective to width) the stronger the wall becomes.
Short walls too. I just looked at a 8' tall screen wall (extending about 20' past the end of the home) that was deflecting about 5". The wall is a double wythe brick masonry wall. The only reason it has not fallen is because it is now bearing on a fence post, which is about to give out.

My point was not that masonry doesn't deflect less. My point was that masonry is very prone to moisture issues just in different ways than wood. Masonry cracks easier and thus must have a bigger cross section to prevent the deflection, because if masonry deflects even a little tiny bit, it will crack.

Also adding more axial load to masonry only improves its strength if the axial load is through the centroid of the wall section. If it is not through the centroid then the eccentricity of the load will actually induce more deflection into the wall.
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Old 04-11-2009, 10:03 AM   #20
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Way off base on the purpose of reinforcement in a masonry wall. The steel reinforcement is there to increase the tensile strength of the wall and does little to increase the stiffness. Even plain grout does as much good as reinforcement. Some rebar is only used for continuity, as in a bond beam that is normally not a structural element.

A noted and respected engineer and code author, Jim Amrhein, always said put as little as possible into the wall so you know better what you have. - The Brazilian engineers have followed this thinking when they designed hundreds of 15-22 story 6" masonry loadbearing apartments using a partial grouting and had some walls that had no structural reinforcement except for the "continuity" reinforcement around openings and a bond beam/slab.

Dick

If you make those simplistic assumptions to ease the calculations, like many of us professional structural engineers do, you can fall into the "idealistic" trap and forget the real mechanics of the wall during performance. These assumptions always get in the way of accuracy and even creep into the codes. That is why we wrote the ACI 530 code to provide for several different methods of design (Empirical, Allowable Stress, Strength Design and Prestressed).

All codes have deflection requirements, but as you see the deflections for masonry are far less than lightweight construction (wood, steel stud). It is ironic that the brick veneer on a lightweight wall is far stiffer then the back-up wall. While investigating the damage from the Northridge earthquake many years ago, I saw many structures that had the interior walls destroyed because of internal loading and connections, while the exterior veener was still standing around the pile of rubble. Naturally, everything was demolished during the rebuilding. This was near the dam where the accelerations were very unusual.

Steel reinforcement does have its place if the engineers know how to use it. I saw some 24' wall panels (6" and 8" block) that were tested in flexure. They reached a deflection of 3 times the theorhetical amount and recovered without a crack. - One panel was cut to a narrower width so it could be used as a diving board
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Old 04-11-2009, 01:07 PM   #21
 
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Dick,

I clearly stated that reinforcement is added to masonry to increase its ductility. Ensuring ductility in a masonry design is a balancing act between the capacity of compression region and the capacity of the tension region.

Grout is not a substitute for steel reinforcement in no way. Grout and concrete have no where near the tensile capacity of of steel. There are many cases where the tensile capacity of the masonry and grout assembly are sufficient and reinforcement is not required for bending or shear. In many cases the extremely heavy weight of this type of assembly helps increase the bending capacity of a wall because the weight can hold the tension face together. This heavy assembly without reinforcement will not work in high seismic areas.

Quote:
All codes have deflection requirements, but as you see the deflections for masonry are far less than lightweight construction (wood, steel stud). It is ironic that the brick veneer on a lightweight wall is far stiffer then the back-up wall. While investigating the damage from the Northridge earthquake many years ago, I saw many structures that had the interior walls destroyed because of internal loading and connections, while the exterior veener was still standing around the pile of rubble. Naturally, everything was demolished during the rebuilding. This was near the dam where the accelerations were very unusual.
I've stated more than once that masonry has a bigger cross section that that of wood, resulting in the lower deflection. For example an 8" cmu has a great moment of interia that a 2x8 wood member does (also the modulus of eleasticity is much higher in steel and wood than it is for masonry). The higher moment of inertia is the result of the lower deflection. Again masonry is not as ductile as wood or steel, thus the need for the larger cross section and moment of inertia.

I will also point out that heavier, more rigid, and less ductile structural elelments will attract seismic forces much more so than a member that is light and ductile. Proper amounts and placement are extrememly critical in masonry design for seismic.

Another thing of note is that if a masonry wall defelcted three times the allowable code limit, then it for sure cracked. If it deflected that much then the moment on the masonry was great than the cracking moment for the section. This is why the reinforcment was needed, because without it the wall would have been destroyed as it would not be ductile enough to return to its original shape. I can asure that the tension face cracked the masonry but did not yield the steel.
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Old 05-21-2009, 09:09 PM   #22
 
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Dryvit experiation date?


We purchased dryvit from a friend that wanted to change colors and so got it at a great deal. We are looking for a professional to install. One person we talked to said it is no good if over one year old. What we purchased is about 1 1/2 years old. Is this true? Do you have any recommendations?
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Old 05-22-2009, 06:51 AM   #23
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I had a client that was going to use dryvit on a 13,000 sq/ft home. But after talking to neighbors found complaints that it whistled during periods of high winds. Changed to stone and brick siding. Dryvit needs a good drain plain behind it to assure no moisture problems affecting a wood framed house. This step alone is more than vinyl siding.
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Old 03-27-2010, 09:41 AM   #24
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Notice who is bad mouthing Dryvit, brick and concrete masons. Do you think that they are a bit biased? Dryvit, STO, Synergy, Parex and a few other materials are FAR BETTER than the other sidings if done right. You nailed it when you said that the problem was application. What most don't mention is that the application problem was more than just not following the proper installation specs.It was also what it was being applied over. As far as class action suits, ask these guys how many were won? Stucco when done correctly offers far better insulation and aesthetic possibilities than the other sidings. Hey you brick guys, tell him some stories about removing damaged brick walls and finding out that the brick was the only thing holding up the house due to wood rot.
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Old 03-27-2010, 09:54 AM   #25
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Well, Dryvit sure doesn't work on the Coast. I've torn it off a couple houses due to constant leak issues. What a MESS that was.
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Old 03-27-2010, 10:09 AM   #26
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any exterior siding has potential for badness
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Old 03-27-2010, 12:46 PM   #27
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Quote:
Originally Posted by James Gentry View Post
Notice who is bad mouthing Dryvit, brick and concrete masons. Do you think that they are a bit biased? Dryvit, STO, Synergy, Parex and a few other materials are FAR BETTER than the other sidings if done right. You nailed it when you said that the problem was application. What most don't mention is that the application problem was more than just not following the proper installation specs.It was also what it was being applied over. As far as class action suits, ask these guys how many were won? Stucco when done correctly offers far better insulation and aesthetic possibilities than the other sidings. Hey you brick guys, tell him some stories about removing damaged brick walls and finding out that the brick was the only thing holding up the house due to wood rot.
I'll bad mouth dryvit and the like and I am neither a bricklayer or a mason. I am a retired attorney and I worked on millions of dollars of cases of dryvit gone bad.
- Yes, it was almost always because of installation defects or improper modification. Seems like no one knows how to do this right.
- No, it was not at the coast, it was central Oregon.
- and Yes, the homeowner ALWAYS gets SCREWED.
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