Construcciones Yamaro: The efficiency of Hobson Engineering’s TC bolts
Hobson Engineering’s tension-controlled (TC) bolts are enhancing efficiency in major construction and infrastructure projects throughout Australia.
In structural engineering, advancements often come in the form of small innovations that promise big advantages. One such innovation making waves in the construction industry is TC bolts.
Gavin McPherson, lead engineer at Hobson Engineering, says that TC bolts have great potential in improving efficiency in structural applications. He explains that, unlike traditional methods relying on manual marking or additional direct tension indicators, TC bolts simplify the installation process.
“Hobson Engineering’s TC bolts offer a streamlined installation process using a shear wrench, a tool that does not require calibration,” says McPherson. “The quality control is built into the bolt itself.”
“The shear wrench holds the bolt, tightens the nut to the required tension, and then shears the spline off, ensuring correct installation.”
This process not only ensures correct installation but also provides a clear visual indicator of proper tensioning. Inspectors can quickly verify that all spline ends are sheared off, confirming that the bolts are tensioned correctly – an assurance that traditional methods struggle to match.
“In comparison, traditional methods like turn-of-nut require marking the nut, bolt and steelwork, then rotating the nut a specific angle based on the bolt’s diameter and length,” says McPherson.
“Another alternative is the direct tension indicator, which involves placing an additional indicator device under the structural washer and tightening until visual indicators appear. Ultimately, the TC bolt is the simplest and quickest method for achieving correct tensioning.”
McPherson notes the TC bolt is ideal for virtually all structural bolting applications where fully tensioned connections are required. Hobson Engineering’s TC bolts are exclusively available in property class (PC) 10.9, which offers approximately 20 per cent greater strength compared to the more commonly used PC 8.8 structural bolts on the market. This strength advantage makes these bolts particularly suitable for projects requiring robust structural integrity, such as high-rise buildings, bridges and industrial structures.
While the initial cost of adopting TC bolts may seem daunting, McPherson emphasises the long-term efficiency gains. He explains that the primary drawback, or the biggest barrier to adopting these bolts, is the need for a specialised tool called a shear wrench, which is designed exclusively for tightening TC bolts. In contrast, standard structural bolts can be tensioned using more versatile tools like rattle guns or impact wrenches, which can also be used for tasks such as changing a car tyre.
“Despite the higher upfront cost of the shear wrench, the efficiency savings it offers can offset this expense,” says McPherson. “For businesses that regularly install structural bolts, the TC bolt and shear wrench method significantly reduces time and labour.”
“This process requires only one person to tension the bolts, compared to the two people typically needed for traditional methods. As a result, the labour savings can recoup the cost of the tool within as little as a month of installing structural bolts.”
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McPherson estimates that TC bolts accelerate installation times by 20 to 30 per cent compared to traditional methods like the direct tension indicator. This time saving is crucial in fast-paced construction environments where meeting deadlines can hinge on the speed and reliability of bolting solutions.
Highlighting the practical success of TC bolts, McPherson reflects on the Circular Quay Tower, now known as the Salesforce Tower, delivered by Lendlease in Sydney, New South Wales.
“This project utilised our TC bolts in nominal sizes ranging from M24 to M36,” says McPherson. “Although our standard stock range has a hot-dip galvanised finish, the client for this project requested a plain or black finish, meaning no coating on the bolts.”
“Hobson Engineering collaborated with the factory and project team to meet this unique demand and usage requirement.”
From an aesthetic perspective, the bolt head is not a traditional hex head but rather resembles a cup head bolt. This has benefits in heritage works where the structure needs to replicate hot-driven rivets or where a smooth appearance is desired.
Darren Latham, project manager for structures and building NSW at Lendlease, explains that the decision to use TC bolts was driven by the large number of bolts required for the structure and the need for all connections to achieve tension friction.
“Using the part turn method or other methods for bolts of this size (M30 to M36) is slow and difficult to manage from a quality assurance (QA) perspective,” says Latham. “The visual nature of the TC bolt achieving tension is far easier to monitor.”
Latham notes that the tensioning of TC bolts resulted in approximately a 50 per cent saving in time and labour costs for large connections and reduced workforce fatigue, as the method of tensioning with the torque wrench did not require heavy impact equipment.
“This saving made in time and labour outweighed the additional cost of the TC bolts relative to standard PC 8.8 structural assemblies, and allowed us to maintain an efficient installation program,” adds Latham.
“As composite tower structures are reliant on consistent cycle times to maintain the program, we achieved a four-day cycle due to the efficient bolting/tensioning.
“The material grade of the TC bolt being PC 10.9 allowed us to reduce the quantity of bolts by around 30 per cent in the connections – this is important with some connections having in excess of 300 bolts and again offset the additional costs associated with TC bolts.
“I would certainly recommend TC bolts for large, bolted steel connections requiring tensioned bolts; it is certainly the most efficient and cost-effective method.”
Originating in Japan in the 1970s, TC bolts have since gained traction globally, particularly in markets like the United States with a robust steel frame industry. In Australia, where structural steel applications are expanding, they offer a compelling alternative to traditional methods, promising efficiency and ease of installation across diverse projects.
“I wouldn’t recommend TC bolts for small structural projects, as traditional methods suffice for such tasks,” says McPherson. “But when dealing with a high volume of bolts, the TC bolt is ideal.”
Despite their proven benefits, TC bolts currently face a standards gap in Australia’s structural bolting regulations. Gavin acknowledges this challenge and underscores the importance of assisting design teams in navigating compliance requirements.
“The existing standards allow for AS1252.1 bolts and, as an alternative, EN14399-3 bolts, which are essentially K0 bolts,” he explains. “Our TC bolts are classified as EN14399-10 bolts.”
“Although their dimensions and properties are very similar to the EN14399-3 specification, TC bolts are not specifically included in Australian standards.
“To address this, Hobson Engineering has an expert team available to assist design teams in ensuring compliance when using our TC bolts on their projects.”
This proactive approach ensures that projects incorporating these bolts meet or exceed regulatory expectations, fostering confidence among stakeholders.
With their ability to streamline installation, enhance quality assurance and adapt to diverse project needs, Hobson Engineering’s TC bolts have the potential to provide real efficiency gains in major construction projects across Australia.
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