Fastener Capacity in a Shearwall 1

[Revv]

Hey Guys,

So basically I am trying to derive the capacity of a shearwall considering only the fasteners and not the sheathing. I guess I'm a little lost on how the load looks in a shearwall/acts so I'm confused on how much load each fastener sees and which fasteners see what. Does anyone know of a design example or could you provide guidance on how you would go about designing a single fastener or how the load acts?

Thank you!

 

[DoubleStud]

You need the sheathing to get shear capacity. Maybe I am not understanding the question.

 

[driftLimiter]

The NDS tables for shearwall capacity are based on the panel thickness and the nail size/spacing, as well as the aspect ratio for seismic. We know that the fasteners should be capable of transmitting the wall shear to the boundary elements (sill plate, chords, and double top plate). In reality there is a nonlinear distribution of forces to the fasteners, the fasteners near the corners experience a different direction and magnitude of force than the fasteners near the middle of the wall. However the assumption of uniform distribution of shear is good enough.

Unfortunately for your exercise, the fastener capacity is based on the geometry and material properties of the connected elements, and the fastener size and material....

Without knowing what shear panel is being nailed, the strength of the fastener is meaningless.

 

[Revv]

@doublestud @ drimlimiter so what I'm trying to say is the fastener failure modes only since those normally control. I do have my thickness of sheathing/supporting members but I want to focus on an individual fastener's failure mode and not worry about the sheathing failure modes. I hope that makes sense. So drift, just treat the panel like a beam then?

 

[MotorCity]

You will not be able to derive the shear wall capacities (nor the capacity of any individual components) listed in the NDS tables. They are based on testing of the entire system (sheathing type, fastener type and spacing, etc).

 

[XR250]

I guess I'm a little lost on how the load looks in a shearwall/acts so I'm confused on how much load each fastener sees and which fasteners see what.

All of the fasteners at panel edges carry the same load = unit shear x fastener spacing.
Field fasteners don't really carry anything as they are just there to prevent panel buckling

 

[RPMG]

No, it would not be appropriate to calculate drift by panel bending. Drift calculations must account for bending based on the chords, shear based on the sheathing, and nail slip per the NDS.

I, similar to the engineers above, recommend against calculating fastener forces by rational analysis.

Some good resources for wood and shear wall design include "Design of wood structures ASD/LRFD" and "Seismic Principles" by Paul W. Richards.

 

[driftLimiter]

@Revv

Again the fastener failure mode is a function of the connected materials so you can't really separate them.

I think we all need to know more clearly what your goal is here. Is this an academic exercise? If we can all get a feeling for why you are trying to do this perhaps we could offer some better advice.

As others stated you can't derive the shear wall capacity in the NDS tables because they are empirical, and your assumption that all walls would be controlled by fastener limit states I think is also incorrect, damage to panel near fasteners is an acceptable mode at ultimate limit states.

If this is for academia, you should probably dive into the testing that was done. If this is for design, well IDK why your doing this lol.

 

[AaronMcD]

When I check nail capacity I get numbers very close to the tabulated NDS values. Anywhere from 84%-98% of the tabulated values.

I routinely add extra fasteners at boundary elements/collectors of plywood diaphragms to cover the 25% extra demand required for irregular structures.

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