The Most Technical Parts of Building Retrofit Shear Walls

1/8” crushing of the end studs into the mudsill at the bottom plate can cause over 1″ of at the top on a narrow shear wall.  The magnification factor is the height of the shear wall / width of the shear wall x the amount of mudsill compression.  If the walls are too flexible they will not resist much earthquake force when the whole house deforms (twists) because of the earthquake.

For example, if the end framing member studs on an 8 foot tall by 4 foot wide shear wall  crush the mudsill 1 inch, the deflection at the top will be 2 inches, which is significant.  (8/4 = 2,  x 1 inch compression = 2 inch movement.

Note that a normal shear wall has deflections at the top of the wall in the range of about 0.2 inches at their design loads, so you can see that a little crushing can cause big problems when a narrow shear wall is used in line with other conventional shear walls.

This is more of a deflection issue (lateral movement of the top of the shear wall) rather than a strength issue.   1/8” crushing at the bottom plate can be translated to over an inch of deflection at the top for a narrow shear wall.  The magnification factor is the height of the shear wall / width of the shear wall.  If the walls are too flexible they will not resist much earthquake force when the whole house deforms (twists) because of the earthquake.