Distributed Hold-Down Assembly for Wood Wall Uplift Resistance
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Solution Overview
Problem
Existing tension hold down systems in light frame and wood frame construction fail to effectively resist uplift and compensate for wood shrinkage, leading to instability and potential structural issues during storms, hurricanes, or earthquakes.
Innovation Solution
A hold down system comprising a tie-rod anchored to a concrete foundation, extending through openings in rigid members, with a slack absorber assembly that includes expansion devices and washers to maintain tension and distribute load, ensuring the tie-rod remains under tension and the wall structure is securely anchored.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single-point anchorage system is used, then the structure is simpler to install, but the uplift resistance and structural stability are insufficient
Solution Approach 1:
The anchorage system is segmented into multiple support points (first support and second support) distributed across the rigid member, transforming a single-point anchorage into a multi-point system. This segmentation allows the structure to resist uplift forces more effectively while maintaining installation simplicity, as each support point independently contributes to the overall uplift resistance.
Solution Approach 2:
The system transitions from one-dimensional single-point anchorage to two-dimensional distributed anchorage by positioning supports at different locations (first lateral section and second lateral section) on the rigid member. This dimensional expansion distributes the uplift resistance across multiple points, enhancing structural stability without significantly complicating the installation process.
2Device complexity
If concentrated loading is applied at a single point, then the connection is simpler, but the wood structure experiences higher stress and potential failure
Solution Approach 1:
The compression loading is segmented into multiple contact points between the rigid member and the wood structure (first contact point and second contact point). This segmentation distributes the compressive stress across different areas of the wood, reducing the stress concentration at any single point and preventing potential failure while maintaining a relatively simple connection design.
Solution Approach 2:
The system applies local quality by creating distinct compression zones at different locations on the rigid member. Each support (first support and second support) creates a localized compression area, ensuring that the load is distributed to specific regions of the wood structure where it can be better accommodated, rather than concentrating all stress in one location.
3Ease of operation
If the tie-rod is not kept under continuous tension, then the system is easier to assemble, but the wall stability during storms and earthquakes is compromised
Solution Approach 1:
The system incorporates preliminary action by pre-tensioning the tie-rod during assembly through the nut and washer mechanism. This preliminary tensioning ensures that the tie-rod remains under continuous tension during subsequent loading events (storms, earthquakes), maintaining wall stability without requiring complex adjustment mechanisms during operation.
Solution Approach 2:
The system utilizes parameter changes by adjusting the nut on the tie-rod to achieve the desired tension level during assembly. This simple parameter adjustment (nut rotation) allows the installer to set the tie-rod tension, ensuring continuous tension is maintained under various loading conditions while keeping the assembly process straightforward.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system effectively resists uplift and shear forces, compensates for wood shrinkage, and maintains structural integrity by distributing load across multiple expansion devices, ensuring the wall remains securely anchored and stable under various weather conditions.
Implementation Method 1
the nut exerting pressure on the second rigid member to place the tie rod under tension loading
Implementation Method 2
the tension loading is transferred by the second rigid member to the first and second supports to subject the first and second supports to compression loading
Data Source
AI summary
A hold down system for a building wall comprises a first rigid member and a second rigid member, the second rigid member being vertically spaced apart from the first rigid member, the first rigid member is supported on a horizontal member of a stud wall, the first and second rigid members including first and second openings, respectively; a tie-rod with a lower end portion for being anchored to an anchorage, the tie-rod extending transversely through the first and second openings, the tie-rod dividing the first and second rigid members into a first lateral section on one side of the tie-rod and a second lateral section on a diametrically opposite side of the tie-rod; first support and second support disposed between the first and second rigid members, the first support being disposed in the first lateral section, the second support being disposed in the second lateral section, the tie-rod extending through the first and second rigid members outside of the first support or the second support; and a nut threaded to the tie-rod, the nut exerting pressure on the second rigid member to place the tie rod under tension loading, the tension loading is transferred by the second rigid member to the first and second supports to subject the first and second supports to compression loading, thereby causing the first rigid member to press on the horizontal member of the stud wall via the first and second lateral sections of the first rigid member, thus distributing the compression loading.