The structural integrity of a building can be improved by reinforcing connection points along the continuous load path of a structure.
The important connections as shown in the diagram are:
- Roof to upper floor walls
- Upper walls to lower walls
- Lower walls to main floor
- Main floor to foundation
Strengthening these connections from the roof to the ground helps ensure that the building will be able to adequately withstand the forces associated with earthquake shaking.
Metal brackets and straps are used to strengthen these connections. To be effective, these brackets and straps should be attached at the studs and rafters, not to the plywood sheathing.
When all of the connections are properly reinforced in this manner, a building is less likely to collapse.
The methods for reinforcing the continuous load path vary for each level of a structure.
The connections between the roof and top level walls are strengthened by:
- Properly nailing the roof sheathing to the roof joists and the roof joists to the top of the walls that support the roof
- Adding blocking—short cross beams— between roof joists, especially where the roof meets the exterior walls
- Bracing all roof framing
- Avoiding the use of heavy roof coverings such as concrete tiles
(Illustration points out the methods of reinforcing a roof to upper floor walls: roof bracing and blocking on a home under construction are pointed out. Avoid heavy roofing materials.)
Strengthening the connection between levels can also be accomplished by using properly nailed structural plywood sheathing in specific wall sections. These sections of wall are referred to as shear walls.
- Shear walls must use structural sheathing, must be properly nailed in specific patterns, and must be anchored at the corners
- Shear wall size is specified by building code
Metal straps may also be used to connect the levels of a structure. These straps must be nailed to the studs and not just the sheathing.
(Illustration shows the methods for reinforcing the continuous load path from upper to lower walls. The shear wall is pointed out, in addition to the specific nail pattern and the anchorage at corners.)
The connection between the lower walls and the main floor is strengthened by:
- Adding wood cross beams called blocking between each floor joist at the end of each joist and at all interior load-bearing points
- Adding connection straps between the joists and the top of the foundation
- Ensuring that connections are made to the studs and not just the wall's sheathing
(Illustration shows the continuous load path from the lower walls to main floor. Blocking and connection straps are pointed out.)
The entire structure must be secured to the foundation according to local codes. For example, building codes may require that the structure be bolted to its foundation using ½ inch bolts with a 3 inch square plate washer every 4 to 6 feet along the foundation.
(Photo highlights the continuous load path from the main floor to foundation.)
