5.1 Structural Loads & Systems

Understanding Structural Loads

On the ALE, the Structural Design, Building Materials & Methods of Construction, and Utilities subject does not ask candidates to run structural calculations - that is the domain of the licensed civil/structural engineer. Instead, PRBoA expects an architect to understand load types well enough to conceptually coordinate a structural system into a design at the schematic stage, long before an engineer is engaged. Every building must be designed to safely resist four fundamental categories of load.

Dead Loads

Dead loads are permanent, unchanging loads: the self-weight of the structure itself (columns, beams, slabs, walls) plus permanently attached elements such as roofing, ceilings, fixed partitions, and built-in mechanical equipment. Dead load is calculated from the unit weights of the actual materials used and does not change over the building's life unless the architect specifies new permanent finishes or fixed equipment - for example, retrofitting a heavy garden roof onto an existing structure adds dead load that the original structure may not have been designed to carry.

Live Loads

Live loads are variable, movable loads generated by occupancy: people, furniture, storage, and movable equipment. The National Structural Code of the Philippines (NSCP) sets minimum uniform live loads by occupancy type in Table 205-1. Selected values:

Notice that ground-floor corridors and lobbies carry a higher minimum live load than upper-floor corridors, because ground-floor circulation spaces see denser, less predictable crowd loading. An architect who programs a heavier-occupancy use (an assembly hall, a library stack room, a storage mezzanine) into a space designed for light residential live load is proposing a structural mismatch that must be flagged and coordinated with the engineer.

Wind Loads

The Philippines sits in one of the most typhoon-exposed regions on Earth, and wind loads are lateral (and sometimes uplift) forces that act on a building's exposed surface area. Wind load design is critical for tall or slender buildings (lateral sway) and for lightweight roof systems, where uplift - wind lifting the roof rather than pushing it down - is a common failure mode in typhoon-damaged Philippine buildings. Architects influence wind performance directly through building shape, roof pitch and overhang design, and tie-down detailing at roof-to-wall connections.

Seismic Loads

Seismic (earthquake) loads are lateral forces generated not by wind pressure on a surface, but by the building's own mass resisting sudden ground acceleration - an inertial effect. This is a critical conceptual distinction the ALE tests: wind load is roughly proportional to a building's exposed surface area and shape, while seismic load is roughly proportional to the building's mass. A heavier building of the same footprint (for example, a solid concrete structure versus a lightweight steel one) attracts significantly greater seismic force. Section 5.2 covers seismic design in the Philippine context in depth.

Structural Systems for Architectural Design

Architects conceptually select a structural system based on building type, required span, and loading, coordinating that choice with the design's spatial and aesthetic intent from the earliest schematic sketches.

A post-and-beam (frame) system is the default choice for most Philippine commercial and residential mid-rise construction because it keeps floor plans open and flexible. A bearing wall system is efficient where the plan repeats floor after floor (a dormitory or budget hotel), but walls must align vertically from floor to floor, and the system loses flexibility if the architect later wants to remove or relocate a wall. A shear wall system is rarely used alone for gravity support; it is added specifically to resist lateral force, and Philippine designers frequently concentrate shear walls at the stair and elevator core, which lets the rest of the floor plate stay open while still giving the building an efficient lateral system. A moment-resisting frame trades larger, more heavily reinforced beam-column joints for the freedom to skip walls and bracing entirely, which is why it is popular for lobbies and glazed ground floors. Long-span systems are selected whenever a program needs a large column-free volume; as a rule of thumb, a truss's structural depth runs roughly 1/10 to 1/15 of its span, and the architect must reserve that depth in the section from the earliest massing study, not after the design is finalized.

Load Path: How Loads Reach the Ground

Every load - dead, live, wind, or seismic - must travel along a continuous, unbroken load path from where it originates to the ground: roof loads travel through roof framing into supporting walls or columns, floor loads repeat this pattern at every level, and all accumulated loads ultimately reach the foundation, which distributes them to the soil at a pressure the soil can safely bear. A discontinuous load path - for instance, a shear wall or column that does not continue in an unbroken vertical line from roof to foundation, but instead 'floats' onto a beam or transfer slab - creates a dangerous concentration of force at the transfer point. Recognizing and eliminating discontinuous load paths at the schematic design stage, before the structural engineer is engaged, is one of the most important structural responsibilities the ALE expects of a licensed architect.