12.4 Concrete, Masonry, Steel, and Wood Structural Inspections

12.4 Concrete, Masonry, Steel, and Wood Structural Inspections

Concrete Structural Inspections

Reinforced concrete structures require meticulous field oversight. The inspector must review the formwork for stability, alignment, and cleanliness prior to concrete placement. Formwork must be coated with a non-staining release agent and be tight enough to prevent grout leakage.

• Reinforcement Verification: The inspector must verify the size, spacing, grade (e.g., Grade 60), and placement of reinforcing steel against the approved plans. Particular attention must be paid to shear stirrups, column ties, and horizontal structural members.
• Prestressed and Post-Tensioned Systems: These systems utilize high-strength steel tendons that are stressed after the concrete has cured. The inspector must verify the layout and profile of tendons, ensure that the sheathing is undamaged, and verify clearances. After stressing, the inspector reviews the elongation reports. Elongation measurements must typically be within +/- 7% of the design calculations.
• Joints and Curing: Construction joints must be placed at points of minimum shear and prepared by cleaning and dampening. Curing is critical for strength development; concrete must be kept moist and at a temperature above 50°F (10°C) for at least 7 days (or 3 days for high-early-strength concrete).

Structural Masonry Inspections

Structural masonry inspections focus on mortar, reinforcing steel, and grout placement in Concrete Masonry Units (CMUs).

• Mortar Types: Mortar is classified by compressive strength. IBC Table 2103.2.1 defines Types M, S, N, and O.
  • Type M: High strength (minimum 2,500 psi), recommended for below-grade foundation walls, sewers, and heavy load-bearing structures.
  • Type S: Medium-high strength (minimum 1,800 psi), provides high lateral strength, recommended for seismic and wind-resistant walls.
  • Type N: Medium strength (minimum 750 psi), recommended for general above-grade load-bearing walls.
  • Type O: Low strength (minimum 350 psi), limited to interior non-bearing walls.
• Grouting Methods: Grout is placed in CMU cells to bond units and reinforcement.
  • Low-Lift Grouting: Done in lifts of 5 feet or less. No cleanouts are required, but the grout space must be clean and free of mortar droppings.
  • High-Lift Grouting: Done in lifts up to 24 feet. This method requires cleanout openings at the bottom of each reinforced cell to allow the inspector to verify that mortar droppings and debris have been removed before pouring. Cleanout covers are installed and grouting is performed under continuous inspection.
• Reinforcement Placement: Vertical rebar must be centered or positioned within cells as designed, secured with wire ties or positioners at intervals not exceeding 200 bar diameters to prevent shifting during grouting.

Structural Steel Inspections

Structural steel framing inspections encompass member alignment, high-strength bolting, and structural welding.

• High-Strength Bolting: Fasteners typically comply with ASTM A325 or A490. Connections are specified as either 'snug-tight' or 'pretensioned' (slip-critical). Snug-tight bolts are tightened to bring plies into firm contact, while pretensioned bolts require a specific tension. Verification methods include:
  • Turn-of-the-Nut Method: The bolt is snugged, and then turned a specified fraction of a turn based on bolt length and diameter.
  • Calibrated Wrench: A torque wrench is calibrated daily to apply the required tension.
  • Tension-Control (TC) Bolts: A specialized wrench twists off the splined end of the bolt when the design tension is reached.
  • Direct Tension Indicators (DTIs): Washers with protrusions that flatten as tension is applied; clearance is checked with a feeler gauge.
• Structural Welding: Welds must comply with AWS D1.1 (Structural Welding Code—Steel). The inspector verifies the welder's certification, the electrode type (e.g., E7018), and performs a visual inspection of the weld profile, check for undercut, porosity, slag inclusion, and weld size. Non-destructive testing (NDT), such as ultrasonic or magnetic particle testing, is required for critical welds.
• Erection Tolerances: The structural frame must be erected plumb, level, and aligned. Column plumbness must be within the AISC Code of Standard Practice limits (typically 1 in 500 relative to the base).

Wood Light-Frame Inspections

Wood frame inspections are highly prescriptive. The inspector must verify the load path from the roof down to the foundation.

• Connectors and Fasteners: Verify the installation of hangers, post caps, hold-downs, and hurricane ties. Fasteners must match the manufacturer's specifications (e.g., using structural nails, not roofing or drywall screws, in joist hangers).
• Sheathing and Diaphragms: Wall and roof sheathing (OSB or plywood) serve as shear walls and diaphragms. The inspector must verify nail size (typically 8d or 10d common), nail spacing at the boundaries (e.g., 3, 4, or 6 inches on center) and in the field (typically 12 inches on center), and that nails are not over-driven, which damages the outer plies.
• Engineered Lumber: I-joists, glue-laminated timber (glulams), and laminated veneer lumber (LVL) have strict installation guidelines. Inspectors must verify that I-joist flanges are never cut, notched, or drilled. Webs can only be drilled in accordance with manufacturer-approved charts, keeping holes away from support points.
• Notching and Drilling in Solid Lumber:
  • Floor Joists: Notches are permitted in the top or bottom edges, but they cannot be in the middle third of the span. Notch depth at the ends cannot exceed 1/6 of the joist depth, and notches along the span cannot exceed 1/12 of the depth. Drilled holes must be at least 2 inches from the top and bottom edges and cannot exceed 1/3 of the joist depth.
  • Studs (Exterior/Bearing Walls): Notches cannot exceed 25% of the stud depth. Drilled holes cannot exceed 40% of the stud depth (or 60% if the stud is doubled, and no more than two successive doubled studs are bored). Holes must be at least 5/8 inch from the edge.