Joint Types

RCSC Section 4. Joint Types

Joint Types and Abbreviations

Joint TypeAbbreviation
Snut - TightST
PretensionedPT
Slip-CriticalSC
Source: RCSC 2014

Bolt Thread Conditions in Joints

AbbreviationThread Condition
NThreads Included in the Shear Plane
XThreads Excluded from the Shear Plane
Source: ASTM F3125

NOTE 2—Bolts are sometimes detailed with names such as A325 HS, A325 SC, A325 X or A490 N. These names relate to connection design and bolt installation, but do not change the manufacturing requirements and are preferably not shown on bolt orders.

Snug-Tightened Joints – simplify design, installation and inspection and should be specified whenever pretensioned joints and slip-critical are not required. The applicability is summarized and design requirements, installation requirements and inspection requirements are stipulated for snug-tightened joints per RCSC Specification 4.1. Faying Surfaces in a snug-tightened joint must meet the requirements in RCSC Specification Section 3.2.2. NOTE that there is generally no need to limit the actual level of pretension provided in snug-tightened joints, per RCSC Specification Section 9.1.
Except as required in RCSC Sections 4.2 and 4.3, snug-tightened joints are permitted. Bolts in snug-tightened joints shall be designed in accordance with the applicable provisions of RCSC Sections 5.1, 5.2 and 5.3, installed in accordance with Section 8.1 and inspected in accordance with RCSC Section 9.1. As indicated in RCSC Section 4 and Table 4.1, requirements for faying surface condition shall not apply to snug-tightened joints.

Pretensioned Joints – When pretension is required but slip-resistance is not of concern, a pretensioned joint should be specified. The applicability is summarized and design requirements and inspection requirements are stipulated for pretensioned joints per RCSC Specification Section 4.2. Additionally, pretensioned joints are required by default in some cases per AISC Specification Section J1.10. Faying surfaces in pretensioned joints must meet the requirements in RCSC Specification Sections 3.2 and 3.2.1 but not those for slip-critical joints in RCSC Specification Section 3.2.2.
Pretensioned Joints are required in the following applications:
(1) Joints in which fastener pretension is required in the specification or code that invokes this Specification;
(2) Joints that are subject to significant load reversal;
(3) Joints that are subject to fatigue load with no reversal of the loading direction;
(4) Joints with ASTM A325 or F1852 bolts that are subject to tensile fatigue; and,
(5) Joints with ASTM A490 or F2280 bolts that are subject to tension or combined shear and tension, with or without fatigue. Bolts in pretensioned joints subject to shear shall be designed in accordance with the applicable provisions of Sections 5.1 and 5.3, installed in accordance with Section 8.2 and inspected in accordance with Section 9.2.
Bolts in pretensioned joints subject to tension or combined shear and tension shall be designed in accordance with the applicable provisions of Sections 5.1, 5.2, 5.3 and 5.5, installed in accordance with Section 8.2 and inspected in accordance with Section 9.2. As indicated in Section 4 and Table 4.1, requirements for faying surface condition shall not apply to pretensioned joints.

Slip-Critical Joints – the applicability of slip critical joints is summarized and design requirements, installation requirements and inspection requirements are stipulated in RCSC Specification Section 4.3 except as modified by AISC Specification Sections J3.8 and J3.9. Faying surfaces in slip-critical joints must meet the requirements in RCSC Specification Sections 3.2 and 3.2.2. RCSC defines a faying surface as “the plane of contact between two plies of a joint.” NOTE that the surfaces under the bolt head, washer and/or nut are not faying surfaces.
Subject to the requirements in RCSC Specification Section 4.3, slip-critical joints are rarely required in building design. Slip-critical joints are appreciably more expensive because of the associated costs of faying surface preparation, installation and inspection requirements.
When slip-resistance is required and the steel is painted, the fabricator should be consulted to determine the most economical approach to providing the necessary slip resistance. Special paint systems that are rated for slip resistance can be specified. Alternatively a paint system that is rated for slip can be used with the faying surfaces masked.
Slip-Critical Joints are required in the following applications involving shear or
combined shear and tension:
(1) Joints that are subject to fatigue load with reversal of the loading direction;
(2) Joints that utilize oversized holes;
(3) Joints that utilize slotted holes, except those with applied load approximately normal (within 80 to 100 degrees) to the direction of the long dimension of the slot; and,
(4) Joints in which slip at the faying surfaces would be detrimental to
the performance of the structure.
Bolts in slip-critical joints shall be designed in accordance with the
applicable provisions of Sections 5.1, 5.2, 5.3, 5.4 and 5.5, installed in
accordance with Section 8.2 and inspected in accordance with Section 9.3.

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