How to Install Shear Bracing: Structural Sheathing and X-Bracing

As with other building materials, the load-bearing walls of a steel-framed house must be braced to protect the wall from shear forces and prevent the walls from racking. Shear bracing keeps a house from leaning or falling over. There are two ways of applying shear wall bracing on a steel-framed house: structural sheathing and x-bracing.

OSB or plywood is adequate to keep the wall from racking as long as there are not excessive openings in the wall. In fact, your walls are limited to the percentages of openings given in Table 6.20 of the Prescriptive Method. Shear walls in the Prescriptive Method are also limited to wind speeds of 100 mph, Exposure B or less, and applicable to Seismic Zones 0, 1 and 2.

Further requirements for structural sheathing include coverage and fastening. The plywood must cover the full height of the wall from the top track to the bottom track. And Table 6.14 of the Prescriptive Method recommends No. 8 screws 6 inches on the edges and 12 inches in the field.

In order for structural sheathing to be effective, it should be installed with the long dimension parallel to the stud framing (vertical orientation). (See 6.8.2 in the Prescriptive Method)

	Use your chalkline to layout location of the walls on the subfloor or slab.
	The plywood may be attached to the wall while panelizing or after the wall is plumb and level.
	Make sure that the sheathing is fastened tightly to the steel frame.
	Draw the plywood up tight against the wall with No. 8 self-drilling screws.
	Finish attaching the plywood with screws or pneumatic pins. (See Figure 6.11 of the Prescriptive Method)

X-bracing is another way to obtain shear strength when structural sheathing is not used. X-braces are diagonal steel straps attached to the walls with screws. They are most commonly used with stucco walls or in termite-prone areas. Please note the following when using X-bracing:

You can either cut and tack the strap to the wall during panelization or install the strap after the wall is in place. To install it while the wall is still on the panel table:

	Measure the diagonal section that requires strapping.
	Cut the strap slightly longer than required.
	Tack the strap on each end and in the center of the width of the strap with one No. 8 screw.
	Do not tighten the straps until the walls are plumbed and aligned.

To install X-bracing after the walls have been raised, plumbed, aligned and attached to the foundation or floor deck:

	With one No. 8 screw, attach one end of the strap t o the top track in the center of the width of the strap.
	Prepare your “strap stretcher” by folding and fastening two small strips of steel (ears) around both jaws of a pair of No. 11 C-clamps. You’ll be able to use this strap stretcher again many times, so keep it in your toolbox.
	Screw one ear of the strap stretcher into the other end (bottom end) of the strap.
	Screw the other ear of the strap stretcher into the rim joist, foundation or bottom track.
	Close the clamps of the strap stretcher and draw the strap tighter in small increments until all the slack is removed from the strap.
	Be careful not to apply too much tension and pull the wall out of plumb.
	Screw the clamp end of the strap onto the bottom track with a No. 8 screw.
	Remove the clamp and complete the installation by fastening the designed number of framing screws through the strap into the studs and top and bottom tracks.
	Repeat this for all straps in your design.
	Do not remove your temporary bracing until all permanent bracing is in place.