Self-adjusting hold-down assembly for shrinkage compensation
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Solution Overview
Problem
Existing continuity systems in building construction do not accommodate the shrinkage of wooden members, leading to structural damage during lateral forces like earthquakes due to 'slop' introduced by downward settling, which allows upward movement of building elements.
Innovation Solution
A self-adjusting hold-down assembly featuring a stud-connector, rod-gripper, and gripper-positioning element with a frustoconical bearing surface, allowing the rod-gripper to disengage and reengage with the rod as the building settles, maintaining continuous resistance to upward movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If threaded rods are fixed with respect to the building foundation to resist upward movement, then resistance to lateral forces is improved, but the system cannot accommodate shrinkage of wooden members causing downward settling
Solution Approach 1:
The rod-gripper assembly is designed to move dynamically along the threaded rod as the building settles. The rod-gripper can disengage from the rod and reengage at different positions, allowing the system to adapt to shrinkage while maintaining resistance to upward movement. This dynamic adjustment mechanism resolves the contradiction between fixed resistance and adaptive settlement accommodation.
Solution Approach 2:
The rod-gripper acts as an intermediary between the fixed threaded rod and the settling building structure. It mediates the relationship by allowing controlled movement and disengagement, enabling the system to simultaneously provide upward resistance and accommodate downward settlement through its ability to reposition along the rod.
2Strength
If continuity ties are bolted to vertical wooden members to provide structural support, then lateral force resistance is improved, but shrinkage causes the ties to move downward creating 'slop' in the system
Solution Approach 1:
The rod-gripper assembly maintains continuous resistance to upward movement through its ability to reengage with the threaded rod after disengagement. Even as the building settles and the continuity tie moves downward, the rod-gripper can reestablish contact with the rod, ensuring uninterrupted resistance to lateral forces and eliminating the reliability issue of 'slop' in the system.
3Force
If the rod and nut are vertically fixed to resist upward movement, then resistance to lateral forces is improved, but the nut no longer bears against the end plate when settling occurs
Solution Approach 1:
The rod-gripper assembly is designed to self-adjust as the building settles. When the continuity tie moves downward due to shrinkage, the rod-gripper automatically disengages from the rod and can reengage at a new position without requiring manual intervention. This self-service mechanism maintains the resistance force while adapting to the changed conditions, eliminating the need for external adjustment.
Data Source
AI summary
A continuity system for a building is designed to compensate for the downward settling of building elements over time, which occurs due to the shrinkage of wooden building members. The continuity system comprises one or more hold-down assemblies each having a stud-connector secured to a generally vertical stud, a generally vertical rod inserted into an opening of the stud connector, a rod-gripping member in toothed engagement with the rod above the opening, and one or more positioning elements exerting a downward force on the rod-gripping member. The rod has a lower portion secured to a stable building element such as the building's foundation. The opening of the stud-connector defines a frustoconical bearing surface on the upper surface of a portion of the stud-connector, or on a gripper support element in some embodiments. The rod-gripping member includes a plurality of gripping portions each having a lower surface defining a circumferential portion of a frustoconical shape sized and adapted to conform with the frustoconical bearing surface of the stud-connector.