6.3 Fastener Rejection, Reuse Rules & Field Modifications

Fastener Rejection, Reuse Rules & Field Modifications

The integrity of a structural steel framework relies heavily on the unaltered, uncompromised strength of its fasteners. When bolts are installed, tensioned, and subjected to the harsh realities of a construction site, issues inevitably arise. As a Special Inspector, you must possess a definitive understanding of when a fastener must be rejected, the strict rules governing fastener reuse, and the boundaries regarding field modifications to steel connections. This section outlines the critical RCSC and AISC mandates that govern these non-conformance scenarios.

Fastener Reuse Rules

When a structural bolt is tensioned to its required minimum pretension, it undergoes significant stress. In some cases, this stress permanently alters the mechanical properties of the fastener, pushing it near or into its plastic yield zone. Consequently, reusing a bolt that has already been fully pretensioned is a highly regulated practice fraught with risk.

What RCSC Section 2.3.3 Says

The 2009 and 2014 RCSC Specifications state the same rule: ASTM A490 bolts, ASTM F1852 and F2280 twist-off-type tension-control bolt assemblies, and galvanized or Zn/Al inorganic-coated ASTM A325 bolts shall not be reused. When approved by the engineer of record, black (uncoated) A325 bolts may be reused. Touching up or re-tightening bolts that were loosened by the installation of adjacent bolts is not considered reuse.

The RCSC commentary explains why: A490 and galvanized A325 bolts have enough ductility for one pretensioned installation but are not consistently ductile enough for a second, whereas black A325 bolts can undergo more than one. Its rule of thumb is that a black A325 bolt is suitable for reuse if the nut can be run up the threads by hand. The inspector never authorizes reuse; the engineer of record does. The later RCSC 2020 Specification defines reuse as pretensioning an assembly that has previously been pretensioned, so assemblies that were only snug-tightened and then loosened are not "reused" in that sense.

Touching Up Galvanized Coatings

When galvanized bolts are installed, the physical act of driving the nut often mars or chips the protective zinc coating. To prevent premature corrosion, these compromised areas must be addressed. Touching up galvanized coatings is permitted and required. This is typically achieved using an approved zinc-rich paint applied in accordance with ASTM A780, the standard practice for repairing damaged and uncoated areas of hot-dip galvanized coatings. The inspector must ensure that the contractor properly cleans the affected area and applies the touch-up coating in accordance with the manufacturer's specifications and the project's corrosion protection requirements.

Prohibited Field Modifications

Construction sites are dynamic, and steel doesn't always fit perfectly. However, the methods used by ironworkers to force a fit must not compromise the structural design. The inspector acts as the gatekeeper against unauthorized and dangerous field modifications.

Torch-Cutting and Burning Bolt Holes

One of the most severe violations is the unauthorized use of a cutting torch to create or enlarge bolt holes. Torch-cutting or burning bolt holes is strictly prohibited without explicit, documented approval from the Engineer of Record. RCSC Section 3.3 permits thermally cut holes made by mechanically guided equipment in statically loaded joints, but free-hand thermally cut holes require engineer of record approval, as do thermally cut holes in cyclically loaded joints. Burning alters the metallurgy of the steel around the hole, creating a heat-affected zone that is brittle and highly susceptible to cracking under stress. If holes do not align, the approved method of correction is typically reaming.

Reaming Tolerances

Reaming involves using a specialized drill bit to slightly enlarge misaligned holes. While acceptable, reaming is subject to strict tolerances. The resulting hole cannot exceed the maximum allowable dimensions for standard, oversized, or slotted holes as defined by the AISC Specification. If excessive reaming is required to achieve alignment, the connection is fundamentally flawed and must be evaluated by the EOR. AISC 360 Section M2.5 adds that drift pins must not distort the metal or enlarge holes, and that poor matching of holes is cause for rejection.

Flame Gouging

Similar to torch-cutting holes, flame gouging—using a torch to remove surface defects or modify the shape of a structural member at the connection point—is generally prohibited unless specifically detailed in an approved repair procedure. The rapid heating and cooling cycle compromises the structural steel's integrity.

Unapproved Shim Additions

If gaps exist between connected plies that cannot be closed by snugging the bolts, ironworkers might be tempted to insert steel shims. While shims are a legitimate engineering solution, unapproved shim additions are strictly forbidden. Any shims used must be of the correct material, thickness, and location as specified by the EOR. Inserting random scrap metal into a slip-critical joint, for instance, completely invalidates the engineered friction characteristics of that connection. Legitimate finger shims have limits: AISC 360 Section M2.5 permits fully inserted finger shims with a total thickness of not more than 1/4 in. within a joint without changing the design strength, and RCSC Section 3.3.4 requires finger shims to have the same faying surface as the rest of the plies. RCSC Section 3.1 prohibits compressible materials, such as gaskets or insulation, within the grip of the bolt.

Replacement Protocols for Damaged Fasteners

Throughout the installation process, fasteners can suffer catastrophic damage.

• Broken Bolts: If a bolt snaps during tensioning, the entire assembly (bolt, nut, and washer) must be discarded and replaced.
• Stripped Threads: If the threads on either the bolt or the nut strip during tightening, the assembly has failed. The inspector must reject the fastener, and a new assembly must be installed. Attempting to force a nut past stripped threads or using a die to recut them in the field is a severe safety violation. The RCSC commentary treats nut stripping or cracking as cause for rejection of the installed fastener.
• Damaged Heads: If the head of a bolt is severely rounded off by a slipped wrench, making it impossible to hold or turn securely, it should be replaced to ensure future inspectability and structural reliability.

In all cases of rejection, the inspector must meticulously document the failure, the location, and the subsequent replacement to ensure the final structure relies entirely on sound, uncompromised components.