plusminus20°/40°latitude. Sustainable building design in tropical and subtropical regions

8. Building structures (p. 218-219)
8.1 Principles of building structure and enclosure
The enclosure of a building, the so-called building envelope or façade, has to respond to aesthetic as well as structural and physical goals. In a structural sense one has to distinguish generally between the load-bearing and non-load-bearing walls of a building:

– Load-bearing walls take up all the forces acting upon a building, both vertically and horizontally. They transfer those forces into the foundation or the supporting soil.

– By lateral stabilization, cross-bracing walls contribute to the structural concept of the building as well and thus are also considered load-bearing walls.

– Non-load-bearing walls are generally resisting only their own weight or forces out of wind, which are transferred typically to a primary structure, generally made out of steel or reinforced concrete in today’s buildings.

The building materials that are mostly used in tropical and subtropical climates include wood, clay (adobe), brick, and concrete (Figure 8.1). Wood is used mainly in climate regions that are characterized by large diurnal temperature swings and significant seasonal temperature differences. Earthen construction is used traditionally in hot-arid climates of the Middle East and Africa. In more moderate climate zones, the material brick, often combined with timber construction is common. Concrete as a building material was first used for the construction of the domed hall of the Pantheon in Rome, built 118 to 126 AD, a temple of bearing masonry. Since the end of the 19th century, reinforced concrete has been used as a primary structural material in buildings. This composite material of steel and concrete is considered today one of the most important load-bearing materials in the world of architecture due to its versatile capability to transfer tensile forces via the embedded steel and the concrete’s resistance to compressive forces (Figures 8.2 to 8.4)

As early as in a conceptual phase of a project, the main structural material should be defined. To successfully achieve a cost-effective building, ordering principles of the structure are important to consider, independently of the building being a load-bearing wall or post-andbeam construction. As a result, clear spans of the structural system have great consequences on initial cost. In the case of a load-bearing wall structure, cost increases exponentially with clear span.

The physical demands on a building envelope range from protection against heat loss or gain to humidity control, acoustics, fire protection, and the resistance against driving rain. Building envelopes can be designed as single- or multi-layered assemblies. The structural and physical properties of single-layered or monolithic constructions are solely defined by the material property and its thickness. Consequently, in those wall types just one material must be able to satisfy several multi-functional demands. In a multi-layered envelope construction, on the other hand, the diverse materials of the individual layers can be brought to optimization in order to respond to specific functional requirements.

Besides the composition of the building envelope in general, its constructive design and its interrelationship with the structure – i.e., connections, joints, and energy and sound bridging – play a more or less decisive role.