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A tension control bolt (TC bolt) is a heavy duty bolt used in steel frame construction. The head is usually domed and is not designed to be driven. The end of the shank has a spline on it which is engaged by a special power wrench which prevents the bolt from turning while the nut is tightened.
A tension control bolt is a pre-assembled bolt, nut, and washer used especially in steel frame construction. Also known as a TC bolt, they possess a domed head rather than a hex head because they are installed from a spline on their other end. This spline connects with a special power wrench for installation.
These bolts are ready to be installed with a shear wrench. This wrench has an inner and an outer socket. The inner socket rotates the spline clockwise and the outer socket rotates the nut counterclockwise. Once the correct tension has been achieved, the spline breaks off.TC bolts install easier than heavy hex bolts, DTIs (direct tension indicators), and other construction fasteners.
Tension control bolts are regulated by the AISC, American Institute of Steel Construction, and RCSC, Research Council on Structural Connections. The single most unique feature of the tc bolt is that it is installed with a precisely calibrated shear wrench that takes the guesswork out of achieving the correct preload.
Again, Tension control bolts must adhere to specifications listed by the RCSC, as mentioned before and any degradation of the lubricant on the bolt will cause it to fail inspection. Once the bolts make it to the job site, you must store them properly to protect their lubrication.
If an issue accures with your bolts out in the field, you cannot just re-lubricate them yourself. They must be sent back to the manufacturer to make the corrective measures and then retest.
Also avoid covering the bolts with a tarp outside. Condensation will form causing the lubrication to disapate. On the other hand, hot and dry weather makes the lubrication evaporate.
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They are installed with a specialized electric shear wrench that has an outer socket that turns the nut counterclockwise, while grabbing the spline with the inner socket turning it clockwise. When the proper tension level has been achieved the spline snaps off giving you a visual indication of proper installation.
Tension Control Bolts are the most commonly used fasteners for steel to steel fastening of high strength applications. Also known as tc bolts, these bolts have a dome-shaped head and they can’t be driven using any normal tools. Working with tension control bolts requires a special type of wrench. When the bolt is installed, it gets deformed and its extension gets sheared off because of the torque.
These bolts are capable of preventing slippage because they come with a friction grip connection. TC bolts are pre-loaded bolts and are highly recommended for designs where fatigue must be taken into account. The tension gets evenly distributed across the structure because of the heavy preload. When they are installed in the right manner, tc bolts are extremely efficient in handling vibrations and ensuring that there is no loosening of the structure whatsoever.
TC bolts are also recommended for structures that involve swaying movement of cranes or other heavy equipment because the impact of load reversals can be prevented by preloaded tc bolts. This ensures that the structure doesn’t loosen or disintegrate, and retains its sturdiness. In addition to helping prevent load reversals, tc bolts are also used for the elimination of any possible connection slips.
Therefore, these bolts are created to provide the highest possible longevity to the structure. Moreover, though its fastening mechanism is complicated, tc bolts are easy to use and can be installed by just one person. The inbuilt functionalities of these bolts allow for determining the tensioning required to hold together a structure With the help of this functionality, users can also figure out whether the required tension has been achieved, regardless of how much torque was applied to achieve the tension.
There is no bolt relaxation because at the time of tension, torsional shear is not induced. As they are vibration resistant, lock nuts are not required for tc bolts. It is extremely easy to install tc bolts and the process can be handled by one person. TC bolts of several dimensions can be installed by a single tool.
Heavy calibrated torque wrenches are not required. Though the installation process can be completed by a single person within a short period of time, the overall process is often considered to be a complicated one. As a result, for steel to steel fastening, some construction owners prefer using regular hex bolts.
Before deciding to use tension control bolts, it is important to take one of its important properties into consideration. Once these bolts are removed from the packing, they tend to corrode and lose their lubrication over a period of time. This means that after being opened up, the bolts must be fastened immediately.
This will reduce the bolts’ load-bearing capacity and cause structural deformation. The rust build up also means that fastening the bolts as well as loosening them would require excess torque.
To achieve the correct tension, the wrench turns the nut clockwise, while turning the spline counterclockwise. When the right tension level is reached the spline snaps off – giving consistent, repeatable, and visual indication of accurate tension levels.
F3125 encompasses six other ASTM standards, including A325, A325M, A490, A490M, F1852, and F2280. The F3125 specification is slightly less known and the A325, A325M, A490, A490M, F1852, and F2280 specifications are how our customers refer to these bolts.
TC bolts are used for high strength, steel to steel fastening. It is one of the most commonly used fasteners for high strength applications, even preferred over large hex bolts. The head is dome-shaped and is not designed to be driven with normal tools. It requires a special wrench to work with.
And its spline allows us to gauge when the exact amount of tension is reached by the bolts. Since these bolts come with a fiction grip connection, any slippage is prevented. In designs where fatigue is a crucial consideration, preloaded bolts like TC bolts are recommended. Due to they heavy preload, the tension across the structure is evenly distributed.
This is once again, due to the preload with which these bolts come in. In structures which involve swaying movement of heavyweights like cranes, preloaded TC bolts prevent the impact of load reversals. It ensures that the structure is sturdy and doesn’t loosen or disintegrate. In addition to preventing load reversals, TC bolts also eliminate any possible slips in connections, even across moment resisting components.
Therefore, they are engineered to provide the structure with the highest longevity possible. In addition to that, they are easy to use and require only one person to install despite its complicated fastening mechanism. It comes with inbuilt functionalities to determine the tensioning required to hold the structure together and also helps the user achieve the same.
With Tension Control Bolts:
- Only minimal tool maintenance are required
- There is reduced operator fatigue
- No risk of Hand Arm Vibration Syndrome
- Does not require heavy calibrated torque wrenches
When these bolts are installed properly, they offer a greater advantages than structural hex bolts.
Excluding the storage of these bolts, it is crucial that you torgue them right away instead of simply setting them up for assembly line process. They must not be removed from their storage location until installation.
Storage of TC bolts in high temperature and humidity can reduce the operational efficiency of the bolts.
This will prevent any adverse reaction with the natural elements, ensuring that the bolts do not rust away in storage. But not everyone will be able to secure such containers due to cost factors and storage inadequacies. Sometimes you have to refrain from purchasing the bolts until a few days before installation.
Tension control bolts or twist-off-bolts, are construction fasteners that connect steel joints in structural applications. They are considered high-strength bolts, which contribute to long-lasting steelwork connections.
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TC Bolts are a heavy duty bolt-nut-washer assembly used in steel frame construction. The TC Bolt head is not designed to be driven. The end of the shank has a spline, when engaged by an electric shear wrench it prevents the bolt from turning while the nut is tightened.
When the forces reach the designated torque coefficient, the 12-point spline will shear off, leaving the bolt and nut securing the application at the proper tension.
As every method, the RCSC/AISC specification requires Pre-Installation Verification testing that must be conducted onsite with hardware delivered to site. Test results, by the distributor or manufacturer, satisfy the specification’s requirements. However, test results appearing on supplier Material Test Reports (MTRs) MUST represent all details of bolts being tested. It is especially important that the MTRs represent a coating when bolts are coated.
TC bolts come in limited lengths and diameters. If ASTM F3125/F1852/F2280 Rotational Capacity bolt testing is requested, TC bolts will most likely fail. Special connection clearances must be detailed for wrench access. Frequently more expensive than hex bolts and DTI's. Galvanized twist-off assemblies are in VERY limited supply. Field relubrication is prohibited by code.
Deterioration of the thread condition for any reason will change the torque-tension relationship, and Kulak has shown in an ASCE paper that in as little as three days out of protected storage, one-third of all the twist-off bolts tested did not develop the required pretension at break-off.
Most Searched For Items:- Galvanized Tension Control Bolts
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A490 Tension Control Bolts Made Simple
Immediately, or as soon as possible after snugging, apply the shear wrench to each bolt until the tool twists the splined end off and releases the wrench. If the joint remains snugged for more than a day or even one shift, additional tension calibrator testing may be required.
Pre-Installation Verification:
- Verify the joint has been snug-tightened.
- Verify the splined ends have not twisted off during snugging operations.
- Verify assemblies in the steel work match the condition of bolts tested during pre-installation verification
- Verify the splined ends have properly severed during installation by the installation tool