• Additional Resources

In multi-story light-frame structures, site-built narrow shearwalls must resist extremely high overturning forces, which may require an alternative system to conventional holdowns. Continuous-tiedown systems have emerged as a solution to resist these loads. Two types of tiedown systems are often used in the field to tie off these structures – all-floors-tied-off systems and skipped-floor systems.

Simpson Strong-Tie performed a series of tests and analysis to compare the drift and load capacity between skipped-floor systems and tied off systems. Test results indicated that skipped-floor systems may not meet drift limitation requirements. Analysis shows that if load path differences are not considered, skipped-floor systems may not provide the overturning restraint, which is necessary for multi-story wood frame structures to resist seismic or high wind events. Therefore, skipping floors is not recommended.

SKIPPED-FLOOR SYSTEM:
A single point of restraint for multiple levels
(Not Recommended)

ALL-FLOORS-TIED-OFF SYSTEM:
Overturning restraint provided at each level
(Recommended)

Benefits of All-Floors-Tied-Off Systems:

• Decreased overall construction cost due to smaller post and rod sizes at upper floors.
• Decreased drift due to discontinuous rods not allowing elongation to accumulate and less compression of posts and plates at upper levels.
• More redundancy since the overturning resistance of the lower floors do not depend on the floors above. This is consistent with the way most engineers design buildings for proper load path, where if an element at the top fails, the elements below should still have some redundancy preventing sequential failures.
• Stability during construction – For a skipped-floor system, all floors that are being skipped must be erected before a complete tiedown system is in place, resulting in a potentially unstable structure during construction. For an all-floors-tied-off system, the structure is automatically stabilized since each floor is tied off during construction and does not depend on any type of restraint from the floors above.
• Shrinkage is compartmentalized and does not accumulate at a single floor.

To further understand the benefits of an all-floors-tied-off system, see these other pages:

• Animation: Skipped-Floor System vs. All-Floors-Tied-Off
• Animation: Skipped-Floor System vs. All-Floors-Tied-Off Load Values
• Issues To Consider With Skipped-Floor Systems
• Uplift Load Path: All-Floors-Tied-Off vs. Skipped-Floor Systems
• Test Results Measuring Inter-Story Drift
• FAQs: Skipped-Floor Systems