Expansion Bolts for HSS: An analysis of a new, viable option for HSS connections
Any structural engineer or architect will tell you that there are several challenges associated with HSS connections. Deciding which type of connection to use, additional installation time, and increased cost are all factors that can dissuade a design professional from specifying HSS connections in a project. However, expansion bolts may be the light at the end of the tunnel.
Expansion Bolts 101
Expansion bolts (as seen in the image below) are “mechanical fasteners typically consisting of a bolt, an expansion sleeve, and a cone-shaped nut” that are driven up inside the sleeve to expand the fastener by creating a wedging effect. Unlike conventional connections that are bolted or welded, expansion bolts provide a “blind connection” technique that can easily connect structural members. Because of the decreased installation time when using expansion bolts, the cost and timeframe of the project overall are considerably diminished.
One of the reasons that expansion bolts are suitable for structural connections is due to their load-bearing capacity in both tension and shear applications. They also provide some tolerance to site abuse (e.g., hole size and misalignment) that results in an aesthetically pleasing system. Another advantage of expansion bolts is that they can be manufactured in carbon, alloy, or stainless steel and are available in a wide variety of finishes, making them fit seamlessly into any environment, demanding or otherwise.
The Bottom Line
Engineers and architects are no strangers to complex and diverse requirements for design projects that use HSS. When faced with a short lead time or welding restrictions, the need for HSS connections can compound those complexities. However, the choice to use expansion bolts can make the project go much smoother. With their capacity to handle much higher loads and easy installation process, expansion bolts can make all the difference.
For more information on expansion bolts, or to read about other alternative HSS connections, please refer my original expansion bolts article featured in Structure Magazine.