Required Testing
7.2. Required Testing
A representative sample of not fewer than three complete fastener assemblies of each combination of diameter, length, grade and lot to be used in the work shall be checked at the site of installation in a tension calibrator to verify that the pretensioning method develops a pretension that is equal to or greater than that specified in Table 7.1. Washers shall be used in the pre-installation verification assemblies as required in the work in accordance with the requirements in Section 6.2.
If the actual pretension developed in any of the fastener assemblies is less than that specified in Table 7.1, the cause(s) shall be determined and resolved before the fastener assemblies are used in the work. Cleaning, lubrication and retesting of these fastener assemblies, except ASTM F1852 or F2280 twist-off-type tension-control bolt assemblies, (see Section 2.2) are permitted, provided that all assemblies are treated in the same manner.
Impact wrenches, if used, shall be of adequate capacity and supplied with sufficient air to perform the required pretensioning of each bolt within approximately 10 seconds for bolts to 14-in. diameter, and within approximately 15 seconds for larger bolts.
Commentary:
The fastener components listed in Section 1.3 are manufactured under separate ASTM specifications, each of which includes tolerances that are appropriate for the individual component covered. While these tolerances are intended to provide for a reasonable and workable fit between the components when used in an assembly, the cumulative effect of the individual tolerances permits a significant variation in the installation characteristics of the complete fastener assembly. It is the intent in this Specification that the responsibility rests with the supplier for proper performance of the fastener assembly, the components of which may have been produced by more than one manufacturer.
When pretensioned installation is required, it is essential that the effects of the accumulation of tolerances, surface condition and lubrication be taken into account. Hence, pre-installation verification testing of the complete fastener assembly is required as indicated in Section 8 to ensure that the fastener assemblies and installation method to be used in the work will provide a pretension that exceeds those specified in Table 8.1. It is not, however, intended simply to verify conformance with the individual ASTM specifications.
It is recognized in this Specification that a natural scatter is found in the results of the pre-installation verification testing that is required in Section 8. Furthermore, it is recognized that the pretensions developed in tests of a representative sample of the fastener components that will be installed in the work must be slightly higher to provide confidence that the majority of fastener assemblies will achieve the minimum required pretension as given in Table 8.1. Accordingly, the minimum pretension to be used in pre-installation verification
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is 1.05 times that required for installation and inspection, rounded to the nearest kip.
Pre-installation verification testing of as-received bolts and nuts is also
a requirement in this Specification because of instances of under-strength and counterfeit bolts and nuts. Pre-installation verification testing provides a practical means for ensuring that non-conforming fastener assemblies are not incorporated into the work. Experience on many projects has shown that bolts and/or nuts not meeting the requirements of the applicable ASTM Specification would have been identified prior to installation if they had been tested as an assembly in a tension calibrator. The expense of replacing bolts installed in the structure when the non-conforming bolts were discovered at a later date would have been avoided.
Additionally, pre-installation verification testing clarifies for the bolting crew and the inspector the proper implementation of the selected pretensioning method and the adequacy of the installation equipment. It will also identify potential sources of problems, such as the need for lubrication to prevent failure of bolts by combined high torque with tension, under-strength assemblies resulting from excessive over-tapping of hot-dip galvanized nuts or other failures to meet strength or geometry requirements of applicable ASTM specifications.
The pre-installation verification requirements in this Section presume that fastener assemblies so verified will be pretensioned before the condition of the fastener assemblies, the equipment and the steelwork have changed significantly. Research by Kulak and Undershute (1998) on twist-off-type tension-control bolt assemblies from various manufacturers showed that installed pretensions could be a function of the time and environmental conditions of storage and exposure. The reduced performance of these bolts was caused by a deterioration of the lubricity of the assemblies. Furthermore, all bolt pretensioning that is achieved through rotation of the nut (or the head) is affected by the presence of torque, the excess of which has been demonstrated to adversely affect the development of the desired pretension. Thus, it is required that the condition of the fastener assemblies must be replicated in pre- installation verification. When time of exposure between the placement of fastener assemblies in the field work and the subsequent pretensioning of those fastener assemblies is of concern, pre-installation verification can be performed on fastener assemblies removed from the work or on extra fastener assemblies that, at the time of placement, were set aside to experience the same degree of exposure.
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