• News Update
  • Aug 01, 2024

The Critical Case for Single-Use Fasteners in Rigging Equipment and Hardware

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As a leading specialized supplier of mass timber hardware in North America, MTC Solutions has been privileged to witness and support the exponential growth of mass timber construction across the continent for over a decade. Our journey has been marked by innovation, collaboration, and an unwavering commitment to safety and quality.

With the industry’s expansion comes the need for innovative system solutions and the adoption of new best practices. At MTC Solutions, we pride ourselves on being an engineering-focused company that provides products designed by engineers for engineers. Our dedication lies in developing procedures and methods integrating the latest best practices that not only keep pace with but propel industry advancements.

Today, we are excited to share a crucial insight into why structural self-tapping wood screws should be treated as single-use hardware for rigging applications. Our goal is to empower you, as a design professional, with the knowledge necessary to make informed decisions and offer your clients robust technical advice on safe and reliable rigging practices.
 

Safety Above All

Crew safety is paramount in rigging, as it is in any operation. Ensuring that every crew member returns home safely to their families at the end of the day requires strict adherence to safety protocols.
In North America, rigging safety is regulated by federal or regional authorities or legislations, such as the Occupational Safety and Health Administration (OSHA) in the United States and the Workers Compensation Act in the Canadian province of British Columbia, rather than by specific codes and standards. OSHA, for instance, mandates a factor of safety of 5 for all rigging equipment, a standard that we have incorporated into the latest version of our Rigging Design Guide.

We generally urge caution when consulting design literature from outside North America, as international standards may not always align with the specific requirements and safety needs of our markets.
 

Why Fasteners Should Be Single-Use

(1) Certified Strength Values: Fastener metal strength values specified in Evaluation Service Reports (ESRs) from ICC-Evaluation Service, such as ESR 3178 and ESR 3179, are derived in accordance with specific testing standards. These values apply only to new, unused products that have passed rigorous third-party quality control.

(2) Anti-Friction Coatings: Our fasteners come with an anti-friction coating engineered to reduce friction and thus control and decrease insertion torque during installation. Exceeding the specified insertion torque can weaken the critical fastener metal strength. This coating is effective for a single use and can deteriorate upon reuse, potentially compromising the fastener’s strength.

(3) Thermal Effects: In addition to torque, the drive-in process generates heat through friction as the thread path is bored. The temperature differential between the start and completion of installation is sufficient to induce thermal expansion in the fastener. Once installed, the fastener cools and contracts, seizing itself and tightly engaging its threads within the established thread path.

(4) Inertia and Removal Challenges: Removing seated fasteners requires the initial inertia resulting from thermal contraction to overcome the static friction, which typically exceeds the kinetic friction a fastener experiences during installation. This can subject the fastener to peak torques beyond its specified limit, reducing its metal strength and yielding capacity and therefore increasing the risk of unexpected brittle failure modes.

(5) Tool Specifications: Fasteners, such as structural self-tapping wood screws, should only be installed with low-RPM, high-torque drills with a feather trigger, in one continuous motion. While most common battery-powered hand tools and professional-grade chorded tools with a feather trigger are acceptable, tools with impact mechanisms, such as common impact guns, are not. Impact guns can deliver excessive torques, resulting in frequent and uncontrolled torque. Despite being a seemingly convenient choice for removing seized fasteners, impact guns can compromise fastener metal strength. In addition, these tools can cause fastener fatigue through consistent stop-and-go wrenching motions that repeatedly trigger torsional loading beyond the fastener’s yield strength.

(6) Site Variables: Site conditions for rigging can be unpredictable—wind, crane motions, sudden shifts, and load dynamics can all introduce unexpected loading on rigging hardware. Specifying design professionals account for these variables in design and rely on the consistency of specified fastener strength values as outlined in ESR. Reused fasteners do not guarantee the desired metal strength and may fail under such conditions.

(7) Liability Concerns: Repeated use of fasteners can diminish their metal strength primarily due to torsional effects. This degradation cannot be reliably detected through visual inspection, presenting hidden dangers and potential liabilities for all parties involved.

Reusing structural self-tapping wood screws can lead to visually undetectable strength reductions, undermining their integrity and jeopardizing rigging safety. Given the critical need for reliable and robust solutions in safe material handling, we strongly advocate that fasteners be used only once in these applications.
Thank you for your attention to this important matter. We deeply value your expertise and are here to assist you with any questions or further information you may need. Please do not hesitate to contact us.

MTC Solutions Engineering Team

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