Gravity, wind, and seismic forces cascade downward
All building loads must reach the ground safely. Gravity loads (roof snow, floor live load, self-weight) flow vertically downward: roof loads rest on beams, beams on columns, columns on foundations. Lateral loads from wind or earthquakes cause buildings to sway, introducing shear forces and bending moments throughout the structure. Uplift forces (wind suction on roofs, seismic inertia) pull upward, requiring anchor points and tension capacity that mirror gravity load paths. A complete structural system must handle all three load types simultaneously, creating a comprehensive force network from the highest structural element to bedrock below.
Redundancy and continuity in load distribution
Modern building codes require multiple, independent load paths so that failure of one element does not cause disproportionate collapse. In a moment-resisting frame, columns and beams form rigid joints that resist bending; in a braced frame, diagonal braces carry most lateral load. In a shear wall system, solid concrete or masonry walls resist lateral movement. Most mid-rise buildings combine two or more systems (moment frames with shear walls, for example) to provide redundancy. Continuity between floors, walls, and foundations is critical: a foundation that doesn't anchor the base of columns, or a roof that isn't tied to wall tops, leaves gaps in the load path that can lead to catastrophic failure under extreme loads. Seismic design adds explicit requirements for redundancy and ductility to absorb energy dissipation without sudden failure.