3.4 Structural Steel & Wood Framing

Structural framing in Florida must withstand intense lateral wind forces and uplift pressures caused by tropical storms and hurricanes. General Contractors must master structural wood framing details under the FBC Residential/Building volumes and structural steel erection under AISC and OSHA standards.

FBC Structural Wood Framing & Moisture Protection

Structural wood framing relies predominantly on Southern Yellow Pine (SYP) due to its high bending strength and modulus of elasticity. All dimension lumber must be grade-marked by an accredited agency (such as SPIB).

Moisture Content & Preservative Treatment

• Moisture Limits: FBC Section 2304 specifies that structural dimension lumber must have a maximum moisture content of 19% at the time of enclosure. Engineered wood products (LVL, Glulam, I-Joists) must maintain a moisture content below 15%.
• Preservative-Treated Wood: Wood in direct contact with concrete footings, masonry walls, or soil must be pressure-preservative treated (e.g., ACQ or MCA) or naturally durable species.
• Sill Plate Installation: Treated 2x6 sill plates must be separated from concrete by a foam sill sealer gasket (capillary break) and anchored with 1/2-inch or 5/8-inch anchor bolts spaced a maximum of 6 feet on center (and within 12 inches of plate ends).
• Fastener Corrosion Resistance: Preservative-treated wood chemicals are highly corrosive to standard steel. Connectors and nails used in treated wood must be hot-dip galvanized (ASTM A153) or 304/316 stainless steel.

Continuous Wind Uplift Load Path

The most critical structural requirement in Florida wood framing is the continuous load path. Wind forces striking a roof create massive suction (uplift) that will detach roof framing unless an unbroken chain of structural metal connectors anchors the roof deck down to the foundation.

+-----------------------------------------------------------------------+
|                   CONTINUOUS WIND UPLIFT LOAD PATH                    |
+-----------------------------------------------------------------------+
                                    |
   [ Roof Sheathing ] -------> Ring-Shank Nails @ 6" Grid Spacing
                                    |
   [ Roof Truss / Rafter ] --> Hurricane Metal Strap / Tie (H10A / MTS)
                                    |
   [ Double Top Plate ] -----> Metal Plate Strapping & 24" Splice Lap
                                    |
   [ Stud Wall Assembly ] ---> Wood Structural Sheathing (APA Plywood/OSB)
                                    |
   [ Bottom Plate / Sill ] --> Hold-Down Anchor (HD 5A) / 5/8" Anchor Bolt
                                    |
   [ Foundation ] -----------> Continuous Reinforced Concrete Tie Beam / Footing

Engineered Wood Products (EWP) & Truss Systems

Engineered wood components provide high structural efficiency and span capacity but are susceptible to structural failure if cut or improperly braced.

Key EWP Components

1. Laminated Veneer Lumber (LVL): Layers of thin wood veneers glued with waterproof adhesives; used for high-load headers and beams ($E = 1.9E$ to $2.0E$).
2. Glued Laminated Timber (Glulam): Solid wood laminations bonded together; used for large open-span architectural columns and girders.
3. Wood I-Joists: Structural members consisting of top and bottom solid/LVL flanges bonded to a central OSB web.
   • Strict Field Limitation: Web holes may only be cut in accordance with manufacturer span tables (typically in low-shear areas near mid-span). NEVER notch or drill flanges.

Roof and Floor Trusses

• Truss Design Drawings (TDD): Must be prepared by an engineer and stamped by a Florida Professional Engineer. TDDs must be present on site during inspection.
• Temporary & Permanent Bracing: Must comply with TPI BCSI 1-18 (Handling, Installing, Restraining, and Bracing of Trusses).
• Field Alteration Prohibited: Web members, chords, or plates of a pre-engineered truss cannot be cut, drilled, notched, or altered in the field without written engineering approval from the Truss Design Engineer.

Structural Steel Erection & AISC Standards

Commercial general contractors frequently oversee structural steel erection governed by AISC 360 (Specification for Structural Steel Buildings) and OSHA 29 CFR 1926 Subpart R (Steel Erection).

                      STRUCTURAL STEEL ERECTION
                                  |
       +--------------------------+--------------------------+
       |                          |                          |
       v                          v                          v
FOUNDATION PREPARATION     COLUMN PLACEMENT           BEAM & TRUSS HOISTING
Verify Anchor Bolts        Min 4 Bolts / Column       Min 2 Bolts / Connection
Leveling Nuts / Grout      Safety Deck / Fall Net     Turn-of-Nut Tensioning

OSHA Subpart R Safety & Structural Erection Rules

• Column Base Plates: All structural steel columns must be anchored by a minimum of 4 anchor bolts to prevent overturning during erection.
• Erection Loads: Hoisting cables cannot be released from a structural column or beam until the member is secured with at least two bolts per connection drawn wrench-tight (or equivalent).
• Plumbing-Up: Guy lines and turnbuckles must be installed to align the structure before final tight bolting or welding.
• Fall Protection: Ironworkers engaged in steel erection must be protected from fall hazards at heights above 15 feet (connectors must wear lanyards and have fall protection available up to 30 feet).

Structural Steel Bolting & Welding Quality Control

Structural steel framing joints rely on high-strength bolting or electric arc welding inspected under AWS D1.1 (Structural Welding Code – Steel).

High-Strength Structural Bolting

Structural bolts conform to ASTM F3125 Grade A325 or Grade A490.

1. Snug-Tight Connections: Bearing-type connections where plies are brought into firm contact using an impact wrench or full effort of an ironworker with a spud wrench.
2. Slip-Critical Connections: Mandatory where joints are subjected to fatigue, shear load reversal, or severe hurricane wind vibration. Clamping force prevents joint slip.

Structural Welding & Non-Destructive Testing (NDT)

Welders must be certified under AWS D1.1 for the specific process (SMAW stick, GMAW MIG, FCAW flux-core) and position (1G flat, 2G horizontal, 3G vertical, 4G overhead).

• Fillet Welds: Triangular cross-section weld joining overlapping plates; inspected visually for size, contour, and undercut.
• Complete Joint Penetration (CJP) Groove Welds: Full-thickness butt welds joining heavy column splices or moment frame beams.
• NDT Inspection Methods: CJP groove welds undergo Ultrasonic Testing (UT) or Radiographic Testing (RT) to detect internal slag inclusions, porosity, or lack of fusion.