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TC bolts vs High Strength bolts 3
- Thread starter pond68
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TC stands for tension control, and has to do with their tightening means. As the proper torque is reached the driving head breaks off, twists off or pulls off. Google “A325 TC bolts” and take a look at the various ASTM bolt specs., AISC, and RCSC.
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Also, I have a case where A325 HS was specified for a equipment dunnage on top of a roof.The equipment will have some vibration. The client is asking for the use of A325 TC to avoid some inspection requirements. Is that possible to do the switch?
ASTM A325 is simply a material and geometry specification for a type of high strength bolt.
A325TC bolts look nothing like normal A325 Heavy Hex Bolts but, they both meet the ASTM A325 specification for geometry and material properties.
A325TC bolts look nothing like normal A325 Heavy Hex Bolts but, they both meet the ASTM A325 specification for geometry and material properties.
I imagine the inspection requirements for A325TC's is easier b/c, as dhengr state, the TC bolts have a twist off mechanism that breaks off when the bolt is properly installed with very specific equipment.
TC inspection requirements fall under RCSC 9.2.3
RCSC is a free download and is included in the steel manual AISC 360-05
To my knowledge, the inspection requirements are easier to meet with these bolts than most others
TC inspection requirements fall under RCSC 9.2.3
RCSC is a free download and is included in the steel manual AISC 360-05
To my knowledge, the inspection requirements are easier to meet with these bolts than most others
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pond-
I am not sure what "HS" stands for unless it is "high strength".
If this is the case, you are simply trading one ASTM A325 bolt for another and there is no reason I see why this couldn't be done.
Note that just b/c you are using a TC bolt does not necessarily guarantee you a slip critical joint.
This should be addressed as well.
I am not sure what "HS" stands for unless it is "high strength".
If this is the case, you are simply trading one ASTM A325 bolt for another and there is no reason I see why this couldn't be done.
Note that just b/c you are using a TC bolt does not necessarily guarantee you a slip critical joint.
This should be addressed as well.
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- #10
"High strength" means it is A325 (or A490, or F1852, or ...). Whether it's TC, or heavy hex head, or some crazy type with a pentagonal nut and reverse threads, if it's A325, it's "high strength." By using TC bolts, you're not switching HS for TC. TC are HS.
yes, it could be depending on the design of the bolt and whether they were designed with the threads included or excluded from the shear plane("N" or "X").
You should ensure that the bolts you are swapping are the same in this regard.
I'm not sure why you need fully pretensioned TC bolts in a bearing connection unless vibrations are an issue.
Maybe ConnectEgr will chime in.
This is in his wheelhouse.
You should ensure that the bolts you are swapping are the same in this regard.
I'm not sure why you need fully pretensioned TC bolts in a bearing connection unless vibrations are an issue.
Maybe ConnectEgr will chime in.
This is in his wheelhouse.
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Pond-
read the posts!
The meet the material and geometric requires of ASTM A325.
saying "they are the 'same' except for their tightening means" might be a bit of a blanket statement.
Also make sure your contractor can install TC bolts.
The bolt "head" on a TC bolt is not hex but rather looks like a rivet head. You have to have the proper tools and clearances for installation.
read the posts!
The meet the material and geometric requires of ASTM A325.
saying "they are the 'same' except for their tightening means" might be a bit of a blanket statement.
Also make sure your contractor can install TC bolts.
The bolt "head" on a TC bolt is not hex but rather looks like a rivet head. You have to have the proper tools and clearances for installation.
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Steel Interchange
A325SC Bolts?
How are ASTM A325SC bolts designed and installed? In past projects we typically used A325N and we are now using A325SC. Do both of these types of bolts need to be checked for bearing?
Answer
When dealing with high-strength bolted connections, it is probably best to consider the difference in terminologies pertaining to the bolt type versus that of the connection type. The A325 example refers to the bolt type, while the SC or N refers to required installation details for the connection type and geometry respectively.
Bolt Types
The most common types of bolts used in structural steel applications meet either the ASTM A325 or A490 Standard. There are also twist-off types of bolts, which are equivalent to these bolt types: ASTM F1852 equivalent to ASTM A325, and ASTM F2280 equivalent to ASTM A490. The property requirements are the same for a particular bolt type regardless of the type or details of the connection in which it is to be used.
Connection Types
There are three basic connection types used in structural steel applications: Snug-Tightened, Pretensioned, and Slip-Critical. Descriptions of these connection types and installation requirements can be found in the RCSC Specification (a free download at In all joint types the connection is required to be checked for bearing, which could occur at some time during the life of the structure.
Snug-Tightened Connections: In this connection type, it is required that the faying surfaces of the connection be brought into firm contact. While some pretension of the bolts is required to bring the surfaces into firm contact, there is no specific requirement for a level of pretension that must be induced into the bolts. Thus, while there is some level of clamping force in the connection as a result of the installation requirement to bring the surfaces into firm contact, this type of connection is assumed to provide the least level of safety against slip. The bolts in these connection types are always assumed to be in bearing against the base material, and thus the connection is defined as a bearing connection.
Pretensioned Connections: This type of connection generally is just like a snug-tightened joint, except it also requires that a specified pretension be applied to the bolts in the connection, once the firm contact of faying surfaces has been achieved. It is still a bearing-type joint, and the shear strength design parameters are identical to those of the snug-tightened joint.
Slip-Critical Connections: This connection type is just like a pretensioned connection with the addition of surface preparation requirements to provide the required level of slip resistance. To achieve this goal, there is a specified level of friction coefficient required for the faying surfaces in the connection. After the faying surfaces are brought into firm contact, the bolts are required to be installed to a specified level of pretension, which is the same as that required for a pretensioned connection. Thus, the bolt installation procedure for slip-critical connections is identical to that required for pretensioned connections, the difference being in the preparation requirements for the faying surfaces of the respective connection types.
Threads In or Out of the Shear Plane
One parameter that we have not discussed to this point is the N designation cited in your example. This designation is an indication of where the threads of a bolt are assumed to be located with respect to the shear plane(s) in a connection. The N assumes that the threads of the bolt will be located within the shear plane; an X assumes that the plies are detailed to exclude the threads from the shear plane. The shear strength is reduced if the plies are detailed such that the threads are located within the shear plane.
Kurt Gustafson S.E., P.E
A325SC Bolts?
How are ASTM A325SC bolts designed and installed? In past projects we typically used A325N and we are now using A325SC. Do both of these types of bolts need to be checked for bearing?
Answer
When dealing with high-strength bolted connections, it is probably best to consider the difference in terminologies pertaining to the bolt type versus that of the connection type. The A325 example refers to the bolt type, while the SC or N refers to required installation details for the connection type and geometry respectively.
Bolt Types
The most common types of bolts used in structural steel applications meet either the ASTM A325 or A490 Standard. There are also twist-off types of bolts, which are equivalent to these bolt types: ASTM F1852 equivalent to ASTM A325, and ASTM F2280 equivalent to ASTM A490. The property requirements are the same for a particular bolt type regardless of the type or details of the connection in which it is to be used.
Connection Types
There are three basic connection types used in structural steel applications: Snug-Tightened, Pretensioned, and Slip-Critical. Descriptions of these connection types and installation requirements can be found in the RCSC Specification (a free download at In all joint types the connection is required to be checked for bearing, which could occur at some time during the life of the structure.
Snug-Tightened Connections: In this connection type, it is required that the faying surfaces of the connection be brought into firm contact. While some pretension of the bolts is required to bring the surfaces into firm contact, there is no specific requirement for a level of pretension that must be induced into the bolts. Thus, while there is some level of clamping force in the connection as a result of the installation requirement to bring the surfaces into firm contact, this type of connection is assumed to provide the least level of safety against slip. The bolts in these connection types are always assumed to be in bearing against the base material, and thus the connection is defined as a bearing connection.
Pretensioned Connections: This type of connection generally is just like a snug-tightened joint, except it also requires that a specified pretension be applied to the bolts in the connection, once the firm contact of faying surfaces has been achieved. It is still a bearing-type joint, and the shear strength design parameters are identical to those of the snug-tightened joint.
Slip-Critical Connections: This connection type is just like a pretensioned connection with the addition of surface preparation requirements to provide the required level of slip resistance. To achieve this goal, there is a specified level of friction coefficient required for the faying surfaces in the connection. After the faying surfaces are brought into firm contact, the bolts are required to be installed to a specified level of pretension, which is the same as that required for a pretensioned connection. Thus, the bolt installation procedure for slip-critical connections is identical to that required for pretensioned connections, the difference being in the preparation requirements for the faying surfaces of the respective connection types.
Threads In or Out of the Shear Plane
One parameter that we have not discussed to this point is the N designation cited in your example. This designation is an indication of where the threads of a bolt are assumed to be located with respect to the shear plane(s) in a connection. The N assumes that the threads of the bolt will be located within the shear plane; an X assumes that the plies are detailed to exclude the threads from the shear plane. The shear strength is reduced if the plies are detailed such that the threads are located within the shear plane.
Kurt Gustafson S.E., P.E
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