Tag Archives: Pre-Load

Tension Control Bolts

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Reprint from Hardware & Fastener Components Magazine, Vol. 51

What are Tension Control Bolts?
Tension Control Bolts have a domed head, body, threads, and a splined tip known as the Pin Tail. (See Figure 1) Tension Control Bolts are part of the structural bolting family given by ASTM F3125. Like the other structural bolt variations, these come in two different types, regular and weathering steel and two different strength grades, 125,000 psi and 150,000 psi. The 125,000 psi version is considered Grade A325 and marked as A325TC or A325TC depending on whether it is Type 1 (regular steel) or Type 3 (weathering steel), respectively. The 150,000 psi version is considered Grade A490 and marked as A490TC or A490TC depending on whether it is Type 1 or Type 3, respectively.

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The Fundamentals of Structural Bolting

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Reprint from China Fastener World Magazine, Vol. 48

Most people probably never give the fasteners that hold together most of our modern contrivances a second thought. They simply take for granted that these components will do what they were designed to do. In fact, I believe that few people really appreciate that fasteners are perhaps the lowest cost, most highly engineered components in the products that they are used in. Many times they are truly critical and our lives depend on them working flawlessly.

Although it is likely that this notion can be applied to any application, it is especially true of structural bolting technology. These are the fasteners we depend on every day to hold up bridges, buildings, and other important structures. There is a great deal of information available for the production, installation, and proper use in the consensus standards pertaining to these fastener assemblies. This article will attempt to explore the fundamental principles related to this very important category of fasteners.

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Pre-load: Part II – Tightening Strategies

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Reprint from Fastener World Magazine, Vol. 151

In Part 1 of this series we explored the fundamental concept of Pre-Load and what this means to the fastened joint. Although understanding this concept is a fundamental fastener engineering tenet, one likely cannot stop there and is led to ask the question of how one practically achieves this Pre- Load in the bolted joint. This is where the subject of “tightening strategies” arises. Before we look at the different tightening strategies, let’s briefly review the concepts of pre- load and torque-tension.

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Pre-load: A Primer

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Reprint from Fastener World Magazine, Vol. 150

In the world of fastener engineering, all too often the joint designer gets focused on the wrong things; torque, locking mechanisms, degrees of rotation, and a number of other sundry items, at the expense of focusing on the most important element, joint tension. Of course, this is understandable since torque and angle are the fundamental measures the industry uses in tightening critical joints. Additionally, torque and angle are easily measured and reasonably easily controlled. However, it is the tension that holds the joint together, which makes
it supremely important both at installation and over the service life of the joint. Therefore, it is critical that the joint designer generates sufficient tension so that the joint can perform safely immediately after tightening, but also years down the road after relaxation and other diminishing effects have acted on the joint.

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Strategies To Mitigate Fatigue Failure in Fasteners

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From Fasteners Technology International, August 2013

Although component failures have probably been around for as long as man has been putting things together, it wasn’t until the early to mid nineteenth century that engineers began studying the progressive failure mode that we know today as fatigue. Although highly undesirable, fatigue is a relatively common failure among fasteners and regretfully can lead to some dramatic and even life-threatening consequences. A great deal of progress in understanding fatigue has been made since the nineteenth century, and yet there is still much to be learned. Fortunately, enough is understood today that specific strategies and practices can be employed when a bolt or screw is designed in an application at risk of fatigue failure. This article will look at the basics of fatigue in fasteners and preventative measures that can be adopted to reduce the risk of failure and improve the durability or life of the fastener component.

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