Structural bolts and cladding fasteners

Fasteners in a PEB

A pre-engineered building is assembled entirely with mechanical fasteners. High-strength structural bolts join primary frame members at end-plate and splice connections; commercial-grade bolts fix purlins, girts and bracing; anchor rods connect columns to foundations; and self-drilling screws and rivets fix the cladding, trims and accessories. Each type has its own standards, grades and installation rules, and mixing grades or using the wrong tightening method is a common site error.

Structural bolt grades by region

Bolts, nuts and washers should be supplied as matched assemblies from one manufacturer with lot traceability, particularly for pretensioned joints. Hot-dip galvanized high-strength bolts must have galvanized, lubricated nuts tested with the bolt.

Tightening methods

• Snug-tight: full contact of plies by an ironworker's effort with a spud wrench; used where pretension is not required.
• Turn-of-nut / part-turn: snug, then a specified rotation (RCSC 2020, AS 4100 / AS/NZS 5131, EN 1090-2).
• Calibrated wrench / torque method: torque calibrated daily on the actual assemblies.
• Direct tension indicators: ASTM F959 washers or EN 14399-9 DTIs show when tension is reached.
• Twist-off (tension control) bolts: spline shears at the specified tension (F3125 F1852 / F2280; EN 14399-10 HRC).

Anchor rods and cladding fasteners

Anchor rods are typically ASTM F1554 Grade 36, 55 or 105 in the US, AS/NZS 1252 or 4.6 / 8.8 rods in Australia, and property class 4.6–8.8 rods per ISO 898-1 in Europe – see base plates and anchor bolts and anchor bolts and embeds.

Cladding fasteners are self-drilling, self-tapping screws with EPDM sealing washers, sized to the steel thickness (e.g. 12-14 for purlins up to about 3 mm, 12-24 or heavy-section screws for hot-rolled steel). Durability classes are defined by AS 3566.2 (Class 3 and 4 for coastal and industrial exposure) and by ISO 12944 / ISO 9223 categories elsewhere. Stitching screws and sealed rivets fix side laps and trims. Fastener coatings must match or exceed the durability of the cladding; stainless or bi-metal fasteners are used for severe exposure and aluminium sheet.

Secondary bolts, screws, rivets and anchors

Besides the high-strength bolts in the frame connections, a PEB uses thousands of smaller fasteners. They are low in cost but numerous, and missing or wrong items delay erection more than almost anything else.

• Corrosion classes: AS 3566.2 Class 3 coated screws are typical for general exposure and Class 4 for severe coastal or industrial sites; stainless steel (304 or 316) or bi-metal screws with a hardened carbon drill tip are used with aluminium sheet and in very aggressive environments.
• Approvals: post-installed concrete anchors should be qualified under ACI 355.2 / ACI 355.4 and designed to ACI 318 Chapter 17 (US), to an EAD / ETA under EN 1992-4 (Europe), or to AS 5216 (Australia).
• Isolation: use EPDM or nylon isolating washers where dissimilar metals meet, for example aluminium trims on steel girts.

Sealants, foam closures and tapes that complete the cladding are covered in sundries: sealants, closures, rivets and tapes.

Supply and quality at WSC

World Steel supplies all structural bolts, anchor rods and cladding fasteners for its buildings, specified to the project code and listed by connection on the erection drawings, with mill certificates for high-strength assemblies. Fasteners are packed by connection type to simplify site sorting. See structural bolts and fasteners package, connection design and accessories.