Structural Steel Erection Observation: Connection Types, Bolt Tensioning, Welding Inspection, and Fireproofing

What the architect observes during structural steel erection, including connection types (bolted vs. welded), bolt tensioning methods, welding inspection requirements, and applied fireproofing verification.

ARE · Construction & Evaluation

Overview

Structural steel erection is one of the most critical phases for the architect to observe because connections are the weak links in any steel frame. The architect's observation focuses on verifying that connections match the structural drawings, bolts are properly tensioned, welds meet the specified quality standards, and fireproofing is correctly applied.

Steel connections fall into two broad categories: bolted and welded. Bolted connections use high-strength bolts (A325 or A490) installed in either snug-tight or pretensioned (slip-critical) configurations. Welded connections use fillet welds, complete joint penetration (CJP) welds, or partial joint penetration (PJP) welds. The type of connection affects the inspection requirements: CJP welds on moment frame connections typically require continuous special inspection including ultrasonic testing (UT), while snug-tight bolted connections may require only periodic inspection.

The IBC requires special inspections for structural steel, including high-strength bolt installation, structural welding, and steel frame inspections. These inspections are defined in the Statement of Special Inspections prepared by the structural engineer of record (SER). For high-seismic regions and Risk Category III/IV buildings, structural observations by the SER or a designated registered design professional are also required.

Fireproofing (spray-applied fire-resistive material or SFRM) is applied to structural steel to achieve the required fire-resistance rating. The architect should verify that the SFRM thickness matches the tested assembly thickness and that coverage is complete, especially at connections and beam-to-column joints where application is difficult. Missing or inadequate fireproofing compromises the fire rating of the entire assembly.

Essential

Connection Types and Their Inspection Requirements Snug-Tight Bolted Connections: Snug-tight is the minimum installation condition for high-strength bolts. The bolt is tightened to the point where the connected plies are brought into firm contact. No specific tension verification is required beyond a visual and tactile check. Snug-tight is appropriate for connections in bearing where slip resistance is not required. The AISC Specification allows snug-tight connections for most static loading conditions. Pretensioned (Slip-Critical) Bolted Connections: Pretensioned bolts are tensioned to a specified minimum value (70% of the bolt's tensile strength). The high clamping force creates friction between the faying surfaces that prevents slip under service loads. Slip-critical connections are required where: - Bolts are subject to fatigue loading - Bolts connect elements of the seismic force-resisting system - Bolts are in oversized or slotted holes - Slip would cause serviceability problems Bolt tensioning methods include: 1.

Professional

An architect visits a steel-framed office building during erection of the moment frame connections. The structural drawings show CJP groove welds at the beam-to-column flange connections, with pretensioned A325 bolts at the shear tab. The erection crew has completed welding on the third floor and is ready to begin the fourth. The architect reviews the special inspector's daily reports. One report notes that the welder for beam-column connections on grid line C did not have a current AWS certification for the overhead position (4G) required for the bottom flange welds. The welder had certification for flat (1G) and horizontal (2G) only. The architect flags this to the contractor and the SER. The affected welds must be inspected and potentially re-tested or re-welded. During the same visit, the architect observes the bolt installation crew on the fifth floor.

TLDR

Snug-tight bolts: Plies in firm contact; no tension verification required; suitable for bearing connections
Pretensioned bolts: 70% of tensile strength; verified by turn-of-nut, calibrated wrench, TC bolt, or DTI; required for slip-critical, fatigue, seismic, and slotted holes
Fillet welds: Triangular profile; visual inspection (VT) and possibly MT; most common structural weld
CJP welds: Full thickness; continuous inspection + UT or RT required; used for moment frames and seismic connections
PJP welds: Partial thickness; less inspection than CJP; lower strength connections
Fireproofing (SFRM): Check thickness with pin gauge; verify complete coverage at connections; watch for damage from subsequent trades
Intumescent coating: Alternative to SFRM for exposed steel; painted on; expands in fire; expensive
Welder certification: Must be certified for the specific position and process (1G flat, 2G horizontal, 3G vertical, 4G overhead)
Special inspections: Required for bolt tensioning, welding, and steel frame; defined in Statement of Special Inspections by SER

ELI5

Building with structural steel is like assembling a giant erector set. The beams and columns are manufactured in a fabrication shop and delivered to the site. The critical question is: how well are the pieces connected together? There are two main ways to connect steel pieces: bolts and welds. Bolts come in two flavors. Regular snug-tight bolts are like tightening a nut by hand until it's firm. That's fine for many connections. But for connections that need to resist sliding (like in earthquake-resistant frames), you need pretensioned bolts. These are cranked down so tight that the pieces are squeezed together with enormous force. The friction between the surfaces prevents any movement. Think of it like clamping two boards together so hard they can't slide even if you push sideways. Welds join two pieces of steel by melting them together.

AREConstruction & Evaluation

Structural Steel Erection Observation: Connection Types, Bolt Tensioning, Welding Inspection, and Fireproofing

2 min read241 words

Steel Erection Observation: Connections, Welds, and Fire Protection

Want to track your progress and access more study tools?

Create a free account