Asymmetrical Thread Screw for Hurricane Zone Wood Connections
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Solution Overview
Problem
Conventional screws lack sufficient withdrawal capacity to meet the minimum structural strength requirements in High Velocity Hurricane Zones, necessitating additional fastening components or screws to ensure connection integrity between wooden members.
Innovation Solution
An asymmetrical screw design featuring a continuous thread with varying angles and a transition portion, positioned to enhance the connection strength by resisting movement in both driven and withdrawal directions, thereby increasing the screw's withdrawal capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional screws are used to connect wooden members, then the connection is simple and easy to install, but the withdrawal capacity is insufficient to meet the 700 lbs minimum strength requirement in High Velocity Hurricane Zones
Solution Approach 1:
The thread is divided into two distinct sections: a first section with a first thread profile and a second section with a second thread profile. Each section has different geometric characteristics optimized for specific functions, allowing the screw to achieve high withdrawal capacity without requiring multiple components or excessive complexity throughout the entire thread structure.
Solution Approach 2:
Different portions of the thread are given different local properties. The first section of the thread has a profile optimized for engagement with the first wooden member, while the second section has a profile optimized for engagement with the second wooden member. This local differentiation allows each section to perform its specific function optimally, achieving the required 700 lbs withdrawal capacity.
Solution Approach 3:
The thread profiles in the two sections are asymmetrical to each other, with different pitch, depth, or angular characteristics. This asymmetry allows the screw to create different mechanical interactions with each wooden member, maximizing the withdrawal capacity by optimizing each thread section for its specific engagement requirements rather than using a uniform symmetric design.
2Strength
If multiple screws or additional connection components are used to meet the strength requirement, then the withdrawal capacity requirement is satisfied, but the device complexity and number of components increase
Solution Approach 1:
Multiple thread profiles that would traditionally require separate screws or connection components are merged into a single continuous thread structure. The first and second sections form an integrated thread system on one screw shaft, eliminating the need for multiple separate fasteners or additional connection components while achieving the required 700 lbs withdrawal capacity.
Solution Approach 2:
The single screw with multi-section thread is designed to perform multiple functions simultaneously: engaging with the first wooden member through the first thread section and engaging with the second wooden member through the second thread section. This multi-functional design replaces what would traditionally require multiple separate fasteners or connection components.
3Strength
If a continuous thread with varying angles is used, then the withdrawal capacity increases to meet structural requirements, but the manufacturing precision requirements increase
Solution Approach 1:
The continuous thread is segmented into distinct sections with defined boundaries. Each section maintains a consistent thread profile with specific angles, and the transition between sections occurs at predetermined locations. This segmentation allows each section to be manufactured with standard precision tolerances rather than requiring the entire thread to maintain varying angles with high precision throughout.
Solution Approach 2:
The thread parameters (such as pitch, depth, or angular characteristics) are changed at specific locations along the thread length, creating distinct sections. These parameter changes are implemented at controlled transition points rather than continuously varying, which simplifies manufacturing by allowing standard threading processes to be used for each section with clear start and end points.
Data Source
AI summary
A screw with an asymmetrical thread for securing wooden members together is disclosed. The screw includes a shaft with a head at one end and a tip at the other end. A continuous asymmetrical thread extends along the shaft. The asymmetrical thread has a front surface facing the tip and a rear surface facing the head, the front and rear surfaces each having an angle relative to a plane normal to the shaft. The asymmetrical thread has a first section and a second section. The portion of asymmetrical thread in the first section has front and rear surfaces of first angles with respect to the plane normal to the shaft. The portion of asymmetrical thread in the second section has front and rear surfaces of second angles different than the first angles. The asymmetrical thread includes a transition portion between the first and second sections. The transition portion is positioned along the shaft such that the transition portion is located proximate the interface of the wooden members when the screw secures the wooden frame members together and the head of the screw engages the first of the wooden members.