Structural Systems

The earliest structure in the development of architectural enclosure is the bearing wall. In a bearing wall, the entire length of the wall supports the roof. As walls increase in height, they are thickened to hold their weight and the weight of additional floors and the roof. A simple series of smaller units assembled vertically with the length determined by need, walls may be punctuated with openings to allow for airflow, entry and to create views. Small wooden and the stone beams opened bearing walls. Early towers in castles and fortress often have walls that are five to fifteen feet thick! Corner walls filled with concrete or solid stone resist lateral forces and keep walls vertical. Walls can create round plans, or circle in and out in a wave to support greater heights. Buttresses are wall thickness regularly placed to reinforce the height of the wall. On one 8 ½” x 11” board, present the principles of your structural system, show photos of buildings which are constructed using each structural system. Draw a wall section showing the foundation condition, the wall conditions, and the roof conditions at 1” = ¾,” and finally build a small white model of your structural system and adhere it to your board.

The column or post is the vertical linear element that carries the load of the horizontal member or lintel. From ancient times this system of an enclosure (trabeation) developed from a solid wall as the opening became larger and larger until consolidated loads separately found vertical columnar supports. Vertical loads carried by horizontal members (beams or lintels) to vertical members (columns or posts) and transferred to the ground; infill walls are not load bearing. Vertical members are in compression, and horizontal members are in compression above the neutral axis and tension below the neutral axis. The size of posts and the dimensions of lintels depend on the type of material. For instance, a stone lintel is thicker than a steel lintel because stones are best in compression and need additional thickness to handle the tension; steel lintels, on the other hand, carry both tension and compression with bending or failure. The post and lintel led to the glass curtain wall as a nonstructural covering of tall buildings. The post and lintel system offers the structural opening of views and light. On one 8 ½” x 11” board, present the principles of your structural system, show photos of buildings which are constructed using each structural system. Draw a wall section showing the foundation condition, the wall conditions, and the roof conditions at 1” = ¾,” and finally build a small white model of your structural system and adhere it to your board.

An arch is a structural form that spans an opening. It starts from a horizontal on a spring point where the arc begins upward. Constructed by stone masons, each stone is cut to fit radially against the next one (voussoirs) with the key or centering stone, the final piece that sets all of the other pieces into compression on their lower ends and tension on their tops ends. The round arches of the Romans are the structural system of the Coliseum. Later, Gothic masons created the pointed arch to achieve greater widths and greater heights in stone cathedrals. Key to the structure of the arch is the resisting structure of the walls, buttresses, or thickened piers to the outward diagonal thrust of the loads transferring down the arc and meeting the wall. Draw a wall section showing the foundation condition, the wall conditions, and the roof conditions at 1” = ¾,” and finally build a small white model of your structural system and adhere it to your board.

Once invented, the arch repeated by masons created vaults forming a linear volume. This type of space became popular in castle halls and Romanesque basilicas of early church naves. More advanced forms include the groin and ribbed vault. The intersection of two barrel vaults forms a groin vault. The introduction of thickened ribs allowed for openings and permitted greater heights in halls by eliminating weight. The loads travel through the vault into supporting walls or thickened piers with buttressing. Draw a wall section showing the foundation condition, the wall conditions, and the roof conditions at 1” = ¾,” and finally build a small white model of your structural system and adhere it to your board.

An arch rotated 180 degrees forms a half dome and an arch repeated around a central point 360 degrees forms a dome with a circular plan. Domes over central spaces became very popular during the Renaissance. Innovations in engineering in Italy begin to stack domes for the best proportions on the interior, but with visual height on the outside of the skyline. The Dome in Florence, Italy is a great example of inner acoustic domes and outer visible domes on the skyline. Domes have a compression ring at the top and a tension ring at the bottom. The top ring pushes inward while the bottom pushes outwards; both areas need to be reinforced to hold the dome. Circular domes sat on circular thickened like at the Pantheon in Rome, one of the oldest domed structures in the world. Later the domes were supported by pendentives, or forms, which made the transition between the circular dome base and a square plan. Contemporary renditions include Buckminster Fuller’s Geodesic Dome, pneumatic domes, and retractive cable domes. Draw a section through a dome, its surrounding support, and down through the foundation. Draw in detail the joints between the dome, the roof above, and the wall below. Also, build a small white model of your structural system and adhere it to your board.

A two-dimensional plane system consisting of an assembly of individual straight members arranged in triangular units is called a truss. Look at NEXT.cc’s TRUSS Journey to see the many different types of trusses. The members of the truss transfer load through compression and tension, so all members join together to be free of bending and shear. Trusses consist of a top and lower chords and connecting web members. Chords members are wood, metal, lightweight aluminum, and steel. Draw a section showing the truss, its surrounding support, down through the foundation. Photograph examples of trusses and build a small white model of your structural system and adhere it to your board.

Any material made stable by a skeleton is a framed structure. Early heavy timber construction places large posts spaced far apart supporting floor and roof beams. With the invention of machines to cut and plane wood, the light wood frame, made up of many small wooden members that could be easily handled and assembled by the common nail instead of joinery of timbers became ubiquitous. Based on post and lintel principles, the joints become rigid or fixed. Frame construction is typical in wood, steel or reinforced concrete. Whereas the older timber system infilled with clay tiles, bricks, or earth, manufactured light wood framing uses boarding or shingles. The invention and computerized mass production of steel quickly developed frame construction for early skyscrapers. The Reliance Building in Chicago was one of the first steel-framed structures, raising the structure of its top ten floors in fifteen days! Covered by a variety of curtain walls, rigid steel frames are ideal for tall buildings due to an economy of erection and provision of open space. Reinforced concrete structures combine the compressive strength of concrete with the tensile strength of steel and are the most rigid of all frame constructions. Build three different models one heavy timber, one concrete, and one steel, showing the difference in span and height of the rigid frames.

Shell structures are thin plates with curved surfaces. The shape and material determine the shell’s structural capacity and span. The two major types of shells are cylindrical shells and shells of revolution. Complex shell structures of many shells forms or tensile generated shapes are labeled free form. The plastic or free quality promotes the continuity of the structure and allows for penetration into a variety of interior spaces. The internal structural forces transfer throughout the skin. These stresses are called membrane stresses. In cylindrical shells, the curvature is always perpendicular to the support system. Conoid and hyperbolic paraboloid are two additional types of shells of revolution. Shells create singular volumes. Draw a section through a shell structure. Collect images of different buildings that use shell structures. Build a small shell model.

Pneumatic and tensile structures are interrelated because both the forms and shapes connect to the ground or surrounding structures. Tensile structures make use of twisted steel cables that affixed to water resistant membranes similar to sail fabric, but stronger. The patterns of the membrane sheeting are complex and structural unique to each form and building site. Pneumatic structures are sewn together and then filled with air to open up their interior volume. Research and draw examples of a pneumatic and a tensile structure. The Arche of La Defense in Paris has a Square Modernistic Arch with a roof deck and a Tensile Cafe at the top of its stairs. Build a small model of each and place on your board with photos of existing buildings using these structural systems.

With new material innovations, new forms are possible. Architects and engineers continue to develop new structural systems. With 3D modeling and digital design, almost any pattern or shape is possible. The questions that surround new structural types are are they sustainable? Do they improve the function or experience of the building? Can they be easily cleaned? Are they durable? What is the lifecycle of their production, construction, and longevity? As engineers and architects build taller towers, make forays to other planets, we continue to ask, how does this make our living better?

• Structural systems are still evolving
  • true
  • false
• Choosing a structural system depends upon
  • live loads
  • dead loads
  • material choice & cost
  • material lifecycle
  • all of these and more
• One of the earliest structural systems was the
  • the beam
  • the arch
  • the bearing wall
  • the vault
• The oldest dome is the
  • Pantheon in Rome
  • Hagia Sophia in Istanbul
  • the US Capitol
  • El Doma in Florence
• Structural systems carry the following forces
  • compression
  • tension
  • torque
  • deflection
  • bending
  • all of these depending upon the material, structural type, site bearing capabilities, and climate.