Structural Systems on the ARE
Understanding how structural systems behave, when each is appropriate, and how they transfer loads is fundamental to PPD and PDD. The ARE tests your ability to select and integrate structural systems, not to perform detailed engineering calculations.
Steel
Steel is a high-strength, ductile material with an excellent strength-to-weight ratio, making it ideal for long spans and tall buildings:
- Advantages: High tensile and compressive strength, ductility (absorbs energy before failure), speed of erection, long-span capability, recyclable.
- Limitations: Requires fireproofing (steel loses strength rapidly above 1,000°F), susceptible to corrosion, higher material cost.
- Common systems: Wide-flange beams and columns, bar joists, moment frames, braced frames, composite steel-concrete decks.
- Connections: Bolted (most common in field) and welded (common in shop), with connection type affecting whether a frame behaves as braced, moment-resisting, or a combination.
Concrete
Reinforced concrete combines concrete's compressive strength with steel reinforcement's tensile strength:
- Advantages: Fire-resistant, durable, moldable into complex shapes, good thermal mass, locally available materials.
- Limitations: Heavy self-weight, requires formwork (time and cost), lower tensile strength without reinforcement, long cure times.
- Common systems: Flat plate, flat slab with drop panels, one-way and two-way joist systems (waffle slabs), post-tensioned slabs, concrete moment frames, shear walls.
- Precast concrete: Factory-manufactured members (double tees, hollow-core planks, columns) offer quality control and speed but require transportation logistics and connection design.
Wood
Wood is a renewable, lightweight structural material common in low-rise residential and commercial construction:
- Advantages: Renewable, lightweight, easy to work, good insulator, carbon-sequestering.
- Limitations: Combustible (IBC Type V construction), susceptible to moisture, insects, and decay, limited span and height without engineered products.
- Common systems: Light wood framing (platform and balloon), heavy timber (Type IV), engineered wood products (glulam, LVL, CLT, I-joists), mass timber construction.
- Mass timber: Cross-laminated timber (CLT) and other mass timber products enable taller wood buildings with fire-resistance ratings achieved through charring behavior, now recognized in IBC Type IV-A, IV-B, and IV-C subcategories.
Masonry
Masonry includes concrete masonry units (CMU), brick, and stone, used for both structural and non-structural applications:
- Advantages: Fire-resistant, durable, good compressive strength, thermal mass, noise attenuation.
- Limitations: Low tensile strength (requires reinforcement), labor-intensive, heavy, limited span capability.
- Common systems: Reinforced CMU bearing walls, reinforced brick masonry, composite walls (brick veneer over CMU backup).
System Comparison
| Property | Steel | Concrete | Wood | Masonry |
|---|---|---|---|---|
| Span Capability | Long | Moderate-Long | Short-Moderate | Short |
| Fire Resistance | Requires protection | Inherent | Combustible / charring | Inherent |
| Weight | Light | Heavy | Light | Heavy |
| Speed of Construction | Fast | Moderate | Fast | Slow |
Understand how these systems transfer loads by reviewing Load Path. Reinforce key facts with the Structural Systems Cheat Sheet and PPD flashcards. Sign up free to access all structural practice questions.