Steel Framing Dominates Mid-Rise and Long-Span Commercial Construction
Structural steel is the dominant material for mid-rise and high-rise commercial construction, as well as for long-span applications like sports facilities, warehouses, and exhibition halls. The ARE PPD division tests steel structural concepts at a conceptual level appropriate for architects: understanding how W-shapes work, when to use them vs. open-web joists, and how steel structural systems differ from concrete and wood in behavior and construction sequence.
Wide-Flange (W-Shape) Sections
The wide-flange section (designated W followed by nominal depth × weight per linear foot, e.g., W14×48) is the workhorse of structural steel framing. The W-shape's cross-section consists of two flanges (horizontal plates) connected by a web (vertical plate). This geometry is extremely efficient for bending because material is concentrated in the flanges far from the neutral axis, where it contributes most to bending resistance.
W-shapes are used as: beams (spanning horizontally between columns to support floor and roof loads), columns (supporting vertical loads, with the section oriented for maximum stiffness about the primary bending axis), and girders (primary beams that carry secondary beams and transfer loads to columns). The same shape designation covers a wide range of sizes - from W4×13 (a very small beam) to W44×335 (a massive girder).
Steel Column Behavior
Steel columns fail by one of two modes: yielding (crushing under compressive stress) for short, stocky columns; or buckling (sideways instability) for slender columns. Column buckling is governed by the slenderness ratio (KL/r), where K is an effective length factor that depends on the end conditions (pinned vs. fixed), L is the unbraced length, and r is the radius of gyration of the section. Long, slender columns buckle at much lower loads than they could theoretically yield at - the effective length factor K ranges from 0.5 (fixed-fixed) to 2.0 (fixed-free/cantilever).
Open-Web Steel Joists (OWSJ)
Open-web steel joists are lightweight, prefabricated truss members designed to span long distances while supporting floor or roof loads. They consist of steel chords (top and bottom) connected by a web of diagonal steel angles or rods arranged in a triangular pattern. The open web configuration reduces weight while maintaining depth-appropriate stiffness for long spans, and the openings allow mechanical, electrical, and plumbing systems to pass through the joist depth without lowering the ceiling below the structure.
OWSJ are manufactured to SJI (Steel Joist Institute) standards and come in standard designations: K-series (light-duty roof joists, spans up to 60 feet), LH-series (long-span, up to 96 feet), and DLH-series (deep long-span, up to 144 feet). OWSJ are typically specified by designation (e.g., 20K6), not custom-sized, which simplifies design.
Steel Deck
Steel deck (corrugated sheet steel) is the floor or roof surface that spans between OWSJ or beams. Composite deck (with shear studs connecting it to steel beams) creates a composite beam that is stiffer and stronger than the beam alone, because the concrete slab acts as the compression flange. Steel deck with concrete topping is the most common floor system for commercial steel-frame buildings.
Key Exam Points
- W-shapes: flanges carry bending; web carries shear; efficient for beams and columns.
- Column buckling governed by slenderness ratio (KL/r); longer columns buckle at lower loads.
- OWSJ: prefabricated truss joists; long spans; open web allows MEP routing.
- OWSJ specified by SJI standard designations (K, LH, DLH series).
- Composite deck: steel deck + concrete + shear studs = composite beam action.
Study PPD on AREprep
AREprep’s PPD flashcards cover every concept on this exam with spaced repetition, and the practice exams mirror the real question formats so the actual test feels familiar.