Structural Systems and Foundations
Core Concepts
Understand load paths: gravity (dead, live), lateral (wind, seismic), and how they travel from roof to foundation. Know the difference between bearing-wall and frame structures, and between shallow foundations (spread footings, slabs-on-grade, mats) and deep foundations (piles, drilled piers). Be able to explain soil bearing capacity, frost depth, and why footings extend below the frost line. Recognize the role of lateral bracing, shear walls, diaphragms, and connections.
Traps to Watch
Questions often confuse dead load (permanent, self-weight) with live load (occupancy and environmental). Watch for deflection versus strength: a member can be strong enough yet fail serviceability limits. Another trap is assuming a larger footing fixes a settlement problem caused by poor soil; the fix may be drainage or a deep foundation. Seismic questions test that lateral systems must be continuous and tied together.
Worked Example
A one-story addition sits on expansive clay. Rule of thumb: frost depth governs minimum footing embedment in cold climates, but expansive soils require over-excavation, a moisture barrier, or a deepened perimeter footing regardless of frost. If a question offers "increase footing width" as a fix for heave, it is likely wrong; heave is a soil-moisture problem, not a bearing-area problem.
Key Points
- Trace the complete load path from roof to soil.
- Dead load is permanent; live load is transient or occupancy-based.
- Frost depth sets minimum footing embedment in cold regions.
- Settlement and heave are soil problems, not always footing-size problems.
- Lateral systems must be continuous and positively connected.