Heavy-duty anchors are critical components for construction projects, providing safe and reliable fastening solutions for various applications. In this article Dr Philipp Mahrenholtz, head of product management and marketing at MKT Metall-Kunststoff-Technik GmbH & Co KG, focuses on the most widely used category of concrete anchors – wedge anchors, exploring their history and innovation.
The term heavy-duty anchor comprises of all concrete anchors that are engineered and designed by professionals. There is a wide variety of heavy-duty anchors, namely mechanical anchors such as expansion or undercut anchors, as well as chemical anchors with many sub-types.
The most prominent of these are bolt type expansion anchors, commonly referred to as wedge anchors, as they are an excellent combination of strength and simplicity. They basically consist of a bolt with a conical end embraced by a clip that expands when the bolt is tightened or pulled, pressing against the concrete and transferring the load by friction.
The concept of wedge anchors dates back to the early 20th century when engineers were looking for reliable methods to secure structural and nonstructural components to the then emerging material of concrete. The development of powerful drilling tools made it possible to install them in hardened concrete. Wedge anchors inserted in the borehole and torqued with a nut thrown over the threaded portion of the bolt, offered a simple solution to clamp down any attachments to the concrete structure.
Early wedge anchors were effective but had limitations in terms of load capacity. Over time, innovations in materials and manufacturing methods led to more sophisticated anchors, capable of handling higher loads and more demanding environments.
The performance of heavy-duty wedge anchors took a major step forward with the introduction of product qualification guidelines for third party testing, which defined extensive test programmes and evaluation criteria to provide design data in approval documents, such as the European Technical Approval (ETA). One of the very first wedge anchors to receive an ETA was the MKT BZ+ (ETA – 99/0010).
Over the years, the range of materials the BZ+ is available has been expanded to include zinc plated steel, as well as other various grades of stainless steel, providing the required corrosion resistance and durability. While the product has remained largely the same since its early introduction, its ETA has been upgraded to also include fire rating and seismic performance data. Still sold in the millions, it is the VW Golf of the concrete anchors.
In addition, the load capacity of wedge anchors in tension and shear have been pushed to the limits. Newer generations have a pullout capacity that exceeds the breakout capacity of the concrete, allowing wedge anchors to be used in applications previously reserved for more sophisticated mechanical anchor types such as high-load/sleeve-type expansion anchors or undercut anchors.
This has been made possible by the use of higher strength steel originally used in the automotive industry. Refined clip and bolt properties not only increase the load capacities but also reduce the minimum anchor spacing and edge distance required for installation. As a result, fewer wedge anchors are required to safely transfer the load into the base material, which gives the designer more flexibility in the anchor layout.
Some wedge anchors such as the MKT BZ3 even go a step further and, in addition to being assessed for static and seismic applications (ETA – 19/0619), are also assessed as a variation BZ3 dynamic for dynamic applications to resist fatigue loading (ETA – 20/0117). This type of application was also previously exclusively covered by anchor types such as undercut anchors or bonded expansion anchors, which are more complex and costly.
Wedge anchors are used in a wide range of applications, offering high performance solutions for heavy-duty anchoring in concrete. Their versatility and reliability make them indispensable in the construction industry. Compared to other types of heavy-duty anchors, they are relatively inexpensive, yet easy and quick to install with minimal use of tools, providing a cost-effective and foolproof solution. The history and innovation of wedge anchors reflects the continuous advancements in anchor technology. Wedge anchors will remain the first choice for the years to come.
Having spent a decade in the fastener industry experiencing every facet – from steel mills, fastener manufacturers, wholesalers, distributors, as well as machinery builders and plating + coating companies, Claire has developed an in-depth knowledge of all things fasteners.
Alongside visiting numerous companies, exhibitions and conferences around the world, Claire has also interviewed high profile figures – focusing on key topics impacting the sector and making sure readers stay up to date with the latest developments within the industry.
