Architecture: Building Design & Structural Systems

# Architecture: Building Design & Structural Systems

## Structural Fundamentals

### Load Path Concept
Every building must transfer lds from point of application to the ground through a continuous ld path. Gravity lds (DL + LL) flow: roof/flr surface → slabs → bms → clms → fdns → soil. Lateral lds (WL, EQ) flow: building surface → diaphragms (flrs/roof acting as horizontal plates) → shear walls or braced frames → fdns → soil.

Breaking ANY link in the ld path causes failure. The 1981 Hyatt Regency walkway collapse killed 114 people because a connection detail change broke the ld path — the rod-to-beam connection carried double the intended ld. Every connection must be dsgn for the actual forces passing through it.

### Load Types
**DL**: Weight of the building itself — str framing, slabs, walls, roofing, mechanical equipment, finishes. Constant and predictable. Typical residential flr DL: 10-15 psf. Commercial with conc slab: 50-80 psf.

**LL**: Occupancy and use — people, furniture, moveable equipment. Code-specified minimums: residential 40 psf, office 50 psf, assembly/auditorium 100 psf, library stacks 150 psf, heavy storage 250 psf. LL can be reduced on large tributary areas and on clms supporting multiple flrs (probability that all flrs are fully loaded simultaneously is low).

**WL**: Increases with height (logarithmic velocity profile), varies by geographic region, and creates both positive pressure (windward) and negative pressure/suction (leeward, roof). Hurricane zones require dsgn for 150+ mph winds. Suction forces on roofs and cladding connections often govern dsgn — buildings don't blow over, they blow apart.

**EQ**: Seismic force = mass × acceleration. Heavier buildings attract more EQ force. Ductile materials (stl) absorb energy through deformation. Brittle materials (unreinforced msnr) fail suddenly. Seismic dsgn philosophy: resist minor EQs without damage, resist moderate EQs with repairable damage, resist major EQs without collapse (life safety).

### Structural Systems