5 on 1 wood contruction
5 on 1 wood contruction
(OP)
I am working on a project that is going to have 4 floors of wood and a wood roof on top of a level of precast. I have just started to lay out the shear wall plan. My initial thought is to treat the diaphragm as rigid and push all of the shear into the center corridor walls and partition walls and not use the exterior walls for resisting shear since there is so many openings. The diaphragm will be ¾” T&G plywood on top of wood floor trusses at 24” o.c.. There will be ¾” of gypcrete topping and 2 layers of 5/8” gyp on the underside. The roof diaphragm will just be 5/8” OSB on wood trusses at 24” o.c. The lateral system will be controlled by wind.
I would like some input from those of you that have done this type of construction before. Am I correct in assuming a rigid diaphragm? Are the exterior walls typically ignored for shear on this type of construction? What hold down system works good for the amount of shrinkage to be expected between floors? I have attached a typical floor that shows the walls I am anticipating using for shear.
I would like some input from those of you that have done this type of construction before. Am I correct in assuming a rigid diaphragm? Are the exterior walls typically ignored for shear on this type of construction? What hold down system works good for the amount of shrinkage to be expected between floors? I have attached a typical floor that shows the walls I am anticipating using for shear.






RE: 5 on 1 wood contruction
I have to assume you are in a low seismic region, for with the gypcrete I would expect seismic to control for forces parallel to the long dimension.
Since this is an "L" shaped building, watch out for drag links here. May have to use a few exterior walls... depending.
As for holddowns - Simpson DTS system is good for shrinkage and a=]has auto takeups too if I remember correctly.
Use TJI joists and SPF studs, glulam beams, parallams and microlams, no solid sticks as that is where you will get the shrinkage (in addition to the plates, but can't help that.
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: 5 on 1 wood contruction
RE: 5 on 1 wood contruction
I have broken the diaphragms into sub diaphragms that go from party wall to party wall and from corridor wall to exterior wall. being that the party walls on either side of the corridors do not line up. When the wind force acts perpendicular to grid 'A'. Am i correct in assuming that the shear wall on the opposite of the corridor can not be used to resist the windward force acting perpendicular to grid A since there is no drag linking the two? Trusses span from party wall to party wall which makes it difficult to get a continuous drag. i am analyzing the the diaphragm as flexible in this direction and rigid parallel to grid A. This sounds opposite from what you are recommending.
The two grids at E are from offset columns below.
RE: 5 on 1 wood contruction
Just because you are subdividing the diaphragm doesn't mean it will behave like that. If wind acts normal to grid A, both sides of the corridor will resist that load unless you have an expansion joint separating the two sides (you don't). The question is whether the wind distribution to each shear wall is based on tributary area (flexible diaphragm) or relative stiffness across the entire length (rigid diaphragm). For wind normal to grid A, you will get some flexibility. For the other direction, the diaphragm will be very stiff (excluding the leg of the L).
RE: 5 on 1 wood contruction
RE: 5 on 1 wood contruction
Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.
RE: 5 on 1 wood contruction
RE: 5 on 1 wood contruction
Our code does not permit 100% of the shear to be taken by Gypsum Wallboard. For a four story building, the maximum percentage of total shear force resisted by gypsum wallboard in a story is 80, 60, 40 and 40 for 4th, 3rd, 2nd and 1st story respectively.
BA
RE: 5 on 1 wood contruction
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: 5 on 1 wood contruction
This design is controlled by wind. I am guessing that the 80, 60 40 rule applies to seismic controlled designs. I could not find anything in the 2006 IBC that would restrict gypsum shear walls for wind controlled design
RE: 5 on 1 wood contruction
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: 5 on 1 wood contruction
See Article 10.2.3.3 attached.
BA