Composite Wood Section (Shear Flow)
Composite Wood Section (Shear Flow)
(OP)
I have (2)6x6 timber posts that are stacked on top of one another (acting in bending for a simple span beam as a 6x12), stitched together with lag screws from the top down (connection not shown for architectural purposes). What is that appropriate shear flow to design the lag screw for if the plane stress where to two members come together is zero because it is at member’s centroid for the composite section?
TIA
TIA






RE: Composite Wood Section (Shear Flow)
RE: Composite Wood Section (Shear Flow)
RE: Composite Wood Section (Shear Flow)
RE: Composite Wood Section (Shear Flow)
As you define the "point of application of shear the flow" is at the centroid where the splice occurs. I agree that there is shear flow within the member at d/4 (point of application) but not at the centroid just as you look at the section as a simple beam where V=0 at the midspan. Again, I'm not saying your wrong but I'm looking at a the FBD and just cannot convince myself that shear flow exists at the centroid (point of application).
RE: Composite Wood Section (Shear Flow)
As DRC1 stated, the ybar is the distance from the shear plane (the centroid of the ENTIRE section in this case) to the outer fibers. Pull your mechanics of materials book off of the shelf - it'll have a pictorial description of how to apply the VQ/it formula.
If you "heard" it on the internet, it's guilty until proven innocent. - DCS
RE: Composite Wood Section (Shear Flow)
Use VQ/(It)
Q= the area above the centroidal axis of the composite section (5.5" * 5.5")) times the distance from the cetroidal axis of the composite section to the centroid of the area above (or below) the centroid of the composite section (5.5" - 5.5"/2).
t= 5.5"
V= max shear force
I = moment of inertia of the composite section.
Just think about what you are saying. You are saying that if you lay (2) 6x6 on top of one another they will be as strong and stiff whether you join them or not. That is just not true. There is a difference between (2) 6x6 and (1)12x6.
Also, you know that the shear flow (horizontal shear) at any point must equal the vertical shear at the same point, correct? You also know that that the vertical shear stress is maximum at the centroid of the section. By inspection you can say that the horizontal shear (shear flow) is maximum at the centroid of the section.
RE: Composite Wood Section (Shear Flow)
ybar is the distance from the shear plane under consideration (centroidal axis in this case) to the centroid of the area above (or below) the shear plane (again, centroidal axis in this case). It is not from the shear plane to the outermost fiber.
RE: Composite Wood Section (Shear Flow)
ST04 --- i uploaded a greating training module to clarify everything related to shear, i hope this is helpfull.
h
RE: Composite Wood Section (Shear Flow)
RE: Composite Wood Section (Shear Flow)
RE: Composite Wood Section (Shear Flow)
http://web.umr.edu/~mecmovie/index.html
RE: Composite Wood Section (Shear Flow)
Mike McCann
McCann Engineering
RE: Composite Wood Section (Shear Flow)