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However, many bolted joints are installed in the field. Some of these items are less of a concern in the shop than they are in field. Each of the above items involves logistical considerations and present potential impacts to the cost and schedule of the project. Allowing snug-tight installation eliminates the possibility that it will be required. Arbitration is addressed in Section 10 of the RCSC Specification and ideally, will rarely be required.
BOLT STRENGTH AISC 14TH EDITION 15TH EDITION VERIFICATION
Section N5.6.(a) of the AISC Specification states: “For snug-tight joints, pre-installation verification testing as specified in Table N5.6-1 and monitoring of the installation procedures as specified in Table N5.6-2 are not applicable.Īrbitration. There are inspection tasks required for pretensioned connections that are not required for snug-tight connections. For large, heavy joints, you may actually end up breaking bolts or the splice before you bring the plies into firm contact, and the RCSC Specification addresses this, stating: “If a splined end is severed during this operation, the fastener assembly shall be removed and replaced.” Once firm contact is achieved, the installation must progress “systematically from the most rigid part of the joint in a manner that will minimize relaxation of previously pretensioned bolts.” First, the bolts must be installed in accordance with the requirements in Section 8.1 of the RCSC Specification, which lists the installation requirements for snug-tightened joints. You cannot simply put a TC bolt in a hole and engage the wrench until the spline breaks and expect to have a properly pretensioned joint. TC bolts “shall not be re-lubricated, except by the manufacturer.” For heavy hex head bolts (Grade A325 and A490) this can be done by the user in the field. If the bolts are not properly stored or the final tensioning is delayed, then the bolts may need to be cleaned and relubricated. TC bolts can be particularly sensitive to the condition of the lubricant.
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However, the condition of the bolt and the lubricant is more of a concern for pretensioned joints. These requirements apply equally to snug-tight and pretensioned installations. Section 2.2 of the RCSC Specification addresses the storage of fastener components. At the very least, it involves having a properly calibrated tension calibrator (though not all fabricators, erectors and inspectors have one on hand), scheduling the testing and ordering bolts in sufficient quantities to accommodate both the installation and the required testing.īolt storage and installation conditions. Though pre-installation verification is a relatively straightforward process, we do occasionally hear of issues. The testing shall be done at the start of the work.” This is an extra step that must be performed during the bolt installation for pretensioned connections but is not required for snug-tight conditions. Section 8.2 of the RCSC Specification states: “Pre-installation testing shall be performed for each fastener assembly lot prior to the use of that assembly lot in the work. The installation of pretensioned joints involves the following considerations beyond those for a snug-tight joint: However, simply severing the spline does not ensure that the joint has been properly pretensioned. Therefore, a TC bolt can be tensioned up to the point where the spline is severed, even in a connection specified as snug-tight and designed as a bearing connection. The 2014 RCSC Specification for Structural joints Using High-Strength Bolts (available at does not limit the amount of pretension in a bolt. The bolts also have other potential advantages that have made them attractive to fabricators and erectors. TC bolts can be used in slip-critical, snug-tight and pretensioned connections. We are not surprised that some fabricators prefer TC bolts.
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Based on this, would it make sense to specify all of our connections as pretensioned, since we are presumably getting pretensioned connections anyway? Many of the fabricators we work with regularly use twist-off-type tension-control (TC) bolts regardless of the connection type. We’ve compiled and answered the top 10 most frequently asked questions that our Steel Solutions Center has received. We’re always improving our standards (and our Standards ) at AISC and it only makes sense that we would be inspired by our resourceful users’ questions.