When the motivation is present to instigate a code change, then by all means it should be pursued. I am inquiring what that change should be. I am leaning towards annual inspection of balconies for structural concerns.
Richard L. Flower, P. E., LEED Green Associate
Senior Structural Engineer
Complere Engineering Group, Inc.
If code provisions result in collapse and deaths under foreseeable loading, as a result of foreseeable degradation, then of course the code should be changed.
For a platform suspended high above the ground there clearly should be a back-up support to prevent collapse in the event of failure of the main support.
Specifying adjusted load factors, or more stringent durability control is not the answer. It needs a different approach.
I try to use Parallam Plus on balconies whether they are going to be "water protected" or not. It is rated for greater than 28% moisture content by the American Wood Protection Association. Beams are rated for as high UC4A protection which is good for prolonged wetting and exposure to all weather cycles. Columns are rated as high as UC4B protection which is for high decay potential and saltwater splash applications. The only caveat is that it cannot be resawn in depth or width; it can only be cut to proper length.
The material technical resource sheet is publication TJ-1020 from Weyerhauser.
They could implement a higher preservative treatment requirement for wood used in decks. I haven't read the AWPA U1 in a while, so I'm not sure if this is feasible.
For SI: 1 inch = 25.4 mm, 1 pound per square foot = 0.0479 kPa.
a. Spans are based on No. 2 Grade lumber of Douglas fir-larch, hem-fir, southern pine and spruce-pine-fir for repetitive (three or more) members. b. Ratio of backspan to cantilever span shall be at least 2:1.[/u]
c. Connections capable of resisting the indicated uplift force shall be provided at the backspan support.
d. Uplift force is for a backspan to cantilever span ratio of 2:1. Tabulated uplift values are permitted to be reduced by multiplying by a factor equal to 2 divided by the actual backspan ratio provided (2/backspan ratio).
e. A full-depth rim joist shall be provided at the unsupported end of the cantilever joists. Solid blocking shall be provided at the supported end.
f. Linear interpolation shall be permitted for ground snow loads other than shown.
Your friend's photos show 3 views of one corner of the collapsed balcony, and I think it is an exterior corner. So I don't see how these photos support your assessment. If the joists were indeed pinned at the wall, how do you explain the photo which CTW posted above?
Jeff....you are quoting a prescriptive provision from the residential code. This is a commercial structure (multi-family is commercial, not residential by code).
You, are correct.The engineer sent me photos of the end of the balcony and said it was the connected end. P.276 Breyer "design of wood structures": "cantilever beam systems are not recommended for floors".
Do you think anyone would attempt to design a wood cantilever balcony connecting into a face mounted plate?
If the berkleyside photos are of the balcony pre-collapse then I'd say the design is fundamentally flawed. There is no good that comes from putting a concrete floor over wood and then walling it in from the bottom to prevent inspection of the condition of the structure. I wondered how the people could not feel the sponginess of rotting wood, but it looks like the design was practically created to kill people by preventing any discovery of wood rot, and it was designed to hasten the process.
Why doesn't the membrane extend up and into the dwelling instead of being used to funnel water into the wood? There's no other drain path provided.
Article posted by bookowski shows archt details. Would like to see struct framing plan and detais referenced by architectural drawing.
But I am suspecting the ripped to slope joists or maybe the deck topping, something resulting in ponding.
Childress Engineering Services structural engineer Kevin Liu reviewed the designs and photos, and said the structural design of the wood beams and joists met building codes then in effect. He said the deck's two major cantilever beams -- 1 3/4-inch by 11 7/8-inch each, at each side of the balcony -- appeared to fail, "and then the rest of the joists and beams went down with it."
Based on the details of the original design as shown, there is no means of secondary drainage from the balcony. In a proper design, there should be drainage at the membrane level as well as runoff from the surface of the concrete.
Further, it appears that there was a water intrusion line about a foot off the joist attachment. This indicates a linear breach of the membrane. Was the first joint or the counterflashing joint not adequately sealed? Only a proper investigation will determine.
Even though we're not there and can only speculate, it is clear that the balcony waterproofing design and construction were contributing factors.
