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10.034 Minimum Bolt - Nut Engagement |
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| Q |
I'm working on a project where the bolts were mis-ordered short. When installed according to the plans and specs, the end of the bolt is flush with the face of the nut. How much of a bolt must project beyond the nut when properly installed? -- Special Inspector in San Francisco |
| A |
12/08 - Response prepared by Terry Egland, a principal at Testing Engineers, Inc. and a registered engineer in California Though a common rule-of-thumb is "three threads past the nut", it is just that - a rule-of-thumb, with no basis in fact, In order to arrive at the right answer, we need to follow the reference document chain. If we start with the 2006 IBC, Section 1704.3.3 states "inspect in accordance to AISC specifications", which is a very broad statement. Chapter 35 is a little more specific by designating AISC 360-05 "Specification for Structural Steel Buildings". However, Table 1704.3 gives us AISC 360, Section M 2.5, which gets closer to the heart of the matter. Section M2.5 states "The use of high-strength bolts shall conform to the requirements of the RCSC Specification for Structural Joints Using ASTM A325 or A490 Bolts, except as modified in Section J3. Note that Section J3 makes no statement about bolt - nut engagement. Thus, we have arrived at the collect specifying document, Specification for Structural Joints using ASTM A325 or A490 Bolts, hereafter referred to as the RCSC 2004. Section 2.3.2 of the RCSC 2004 states, "The bolt length used shall be such that the end of the bolt extend beyond or is at least flush with the outer face of the nut when properly installed." So while the old rule-of-thumb won't hurt, the short bolts will work just fine, Reference Documents 2004 RCSC "Specification for Structural Joints Using ASTM S325 or ASTM A490 Bolts" AISC 360-05 Specification for Structural Steel Buildings |
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