Critical Component:
Be sure you're selecting the right fastener
Joe Stager,
Posted
07/01/2010
It is easy for a contractor to come across all sorts of fastening conditions on a typical job site and in most cases an engineering professional selected a specific fastener for the connection.
However, occasionally there may be times when a contractor must select a fastener for a special use or application. Oftentimes the fastener selected was determined based on the availability or price, with little or no thought to load requirements, corrosion resistance or ease of installation. If incorrect fasteners are used that do not meet the minimum load requirements, complete failure of the assembly can occur.
Due to the importance of how fasteners interact with the overall system, engineers consider many factors associated with the connection. They typically analyze service loads, the environment and life expectancy, and specify a fastener based on its mechanical,physical and performance properties to assure it meets the minimum design loads.
Because fasteners are a critical component to how well the system performs, a contractor should take care when selecting for an application. To aid the contractor in choosing the best fastener for the connection, answers to a few basic fastening questions will help in the selection that meets the application and design requirements.
What are the materials being fastened together?
The first step in selecting the proper fastener is to determine the various types of materials that are being fastened (example: is it steel, stainless steel, aluminum or wood). This will allow you to choose a particular type of fastener designed for the substrate and select a compatible material to help minimize galvanic corrosion.
The second step is to determine the thickness of each material (commonly referred to as the “attachment length”), which will allow you to select the appropriate fastener length (refer to “application detail” image).
What are the loads requirements?
From an engineer’s perspective, understanding the expected loads is critical to selecting the proper fastener. There are many different types of loads to consider like tensile, shear and compression. Additionally, an engineer will look for additional loading conditions like expansion and contraction, vibration, or any other force that may affect the fastener performance and determine the ultimate load that may find its way into the connection. Once the loads are established, a fastener is selected based on its physical, mechanical and performance specifications.
Since achieving minimum loads are so vital to the performance of the connection, we recommend contractors consult with a fastener supplier that can provide details on the fastener’s mechanical and performance strengths. They can assist you in selecting a fastener that meets the ultimate load requirement.
What is the environment?
Identifying how the environment may affect the performance of the fastener is significant. For instance, if the location is highly corrosive like a marine environment, using the wrong fastener can lead to early corrosion and a failed connection.
The cost of the fasteners is typically a small percentage of the overall system. It is often better to select fasteners that provide long-life performance and are capable of exceeding the service life of the overall system. Determine the short-term and long-term effects of the environment in order to select a fastener material and finish that will protect against premature failure.
What are the installation requirements?
For a fastener to perform to its optimum level, install them according to the supplier’s recommendations. Be sure that the appropriate installation techniques and correct tooling are used.
As an example, we recommend using the following techniques for installing self-drilling tapping screws. Screws should be installed using a 2,500 rpm maximum screw-gun (use 2,000 rpm or less when installing into 1/4-inch- (6-mm-) thick steel or more). The screw-gun should include a torque control or depth-sensing feature to minimize damage to the sealing washer and reduce the possibility of over-driving the screw to failure (impact tools are not recommended because they can exceed the torque strength of the screw easily, which can cause strip-out and/or screw breakage). Install self-drilling screws perpendicular to the surface using medium pressure. This will allow the screw’s point to drill the steel without causing excessive heat that can reduce drill times. Using these few tips will produce consistent installation and better performance.
What fastener should I use?
For any application, there are numerous types of fasteners from which to choose. When selecting a fastener for the connection, the main objective should be to make sure to meet all load and service requirements. Never substitute a different fastener unless you have obtained approval by the metal building manufacturer, metal roofing manufacturer or engineering professional.
Work with a fastener supplier that can offer technical support, training programs and provide information on the latest fastening technologies. These companies can assist in selecting a fastener that meets the load requirements and assure long-life performance.
Joe Stager is the vice president of product development and marketing at Triangle Fastener Corp., Cleveland, Ohio. For more information, visit www.trianglefastener.com.
www.trianglefastener.com