Structural Systems Comparison
This cheat sheet compares the four primary structural materials tested on the ARE 5.0 PPD exam. Understanding when to use each system is critical. See the Structural Systems topic guide for detailed study.
Material Comparison Overview
| Property | Steel | Concrete | Wood | Masonry |
|---|---|---|---|---|
| Strength-to-weight ratio | Highest | Moderate | Moderate | Low |
| Fire resistance (inherent) | Poor | Excellent | Combustible | Excellent |
| Typical span range | 30'–150'+ | 20'–60' | 10'–30' (solid); up to 80' (glulam) | 12'–25' (lintels) |
| Speed of erection | Fast | Slow (cure time) | Fast | Moderate |
| Cost (relative) | Higher | Moderate | Lower | Moderate |
| Recycled content | High (90%+) | Moderate | Renewable | Low–Moderate |
Steel Systems
| System | Typical Span | Common Application |
|---|---|---|
| Wide-flange beams (W-shapes) | 20'–50' | Office buildings, multi-story |
| Open-web steel joists | 20'–96' | Roofs, floors; allows MEP routing through web |
| Steel trusses | 40'–150'+ | Long-span roofs, bridges |
| Moment frames | 20'–40' bays | Lateral resistance in open floor plans |
| Braced frames | 20'–40' bays | Lateral resistance with diagonal bracing |
| Steel deck (composite) | 8'–15' | Floor systems with concrete topping |
Connection types: Bolted (bearing, slip-critical), welded (fillet, groove, plug), moment connections (rigid), shear connections (simple/pinned).
Concrete Systems
| System | Typical Span | Common Application |
|---|---|---|
| Flat plate | 15'–25' | Apartments, hotels (min slab depth) |
| Flat slab (with drop panels) | 20'–35' | Parking garages, warehouses |
| One-way joist (pan joist) | 20'–40' | Office buildings |
| Two-way waffle slab | 25'–50' | Libraries, galleries (square bays) |
| Post-tensioned slab | 30'–45' | Parking garages, long spans with thin slabs |
| Precast double tee | 30'–80' | Parking structures, warehouses |
| Precast hollow core | 15'–40' | Floors, roofs |
Key concept: Concrete is strong in compression, weak in tension. Reinforcement (rebar, PT cables) handles tension forces. f'c typically 3000–6000 psi for buildings.
Wood Systems
| System | Typical Span | Common Application |
|---|---|---|
| Sawn lumber joists | 10'–20' | Residential floors/roofs |
| Engineered wood joists (I-joists) | 16'–30' | Residential/light commercial |
| Glulam beams | 20'–80'+ | Churches, gyms, long-span roofs |
| CLT (cross-laminated timber) | 20'–30' | Multi-story buildings (Type IV-C, IV-B) |
| Wood trusses | 20'–60' | Residential and commercial roofs |
| Plywood/OSB sheathing | 16"–24" o.c. | Diaphragms, shear walls |
Connection types: Nails, screws, bolts, lag screws, metal connectors (joist hangers, hurricane ties, hold-downs), split ring/shear plate connectors.
Masonry Systems
| System | Common Application |
|---|---|
| CMU bearing walls | Load-bearing walls up to ~4 stories |
| Reinforced masonry shear walls | Lateral resistance |
| Masonry veneer | Non-structural cladding (anchored to backup) |
| Masonry lintels | Openings up to ~12' (steel or reinforced) |
Key fact: f'm (masonry compressive strength) typically 1500–3000 psi. Grouted and reinforced cells provide tension and shear capacity.
Lateral Force-Resisting Systems
- Moment frames: Steel or concrete; ductile, allows open floor plans; more drift
- Braced frames: Steel; X, V, K bracing; stiff but limits openings
- Shear walls: Concrete, masonry, or wood; very stiff; limits openings
- Diaphragms: Floors/roofs transfer lateral loads to vertical elements; rigid (concrete) vs flexible (wood, steel deck)
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