1.5. Types of Structures

Combination of structural elements is referred to as a “structural system”.

A structural system is created when various structural elements work together. These elements can include beams, columns, and other components that support loads. The combination ensures that the structure can withstand the forces acting on it, providing stability and integrity.

Think of a structural system like a team of people working together to lift a heavy object. If each person (structural element) does their part, the object (the load) can be lifted successfully. Each person has a specific role or strength that contributes to the overall effort.

1.5.1 Trusses:

• Used for large spanned structures.
• Consist of slender elements arranged in a triangular fashion.
• Two major types: Planner and Space.
• Convert outside loads to compression and tension forces in members.

Trusses are frameworks that are designed for spanning large distances, such as in bridges or roofs. They are made up of straight components joined together in triangular shapes, which efficiently distribute forces. There are two types of trusses: planar, which lie flat, and space, which are three-dimensional.

Imagine a bridge made of triangles. Each triangle uses its shape to hold up a heavy car effectively, similar to how a triangular roof can support a lot of weight without collapsing. Just like how nature often uses triangles in structures like animal bones for strength, engineers use trusses to achieve stability.

1.5.2 Cables and arches:

• Used to span long distances.
• Cables are flexible and carry the loads in tension.
• Arch achieves its strength in compression.
• Arch must be rigid.

Cables and arches are essential for spanning long distances in structures. Cables can flex and usually bear loads through tension (pulling forces), while arches use compression (pushing forces) to support weight. For an arch to function properly, it must remain rigid to effectively transfer forces.

Consider a suspension bridge, where cables hold up the bridge deck and allow for movement. If you've ever pulled on a string tightly (like a cable), you've experienced tension. In contrast, think of a rainbow; it represents an arch that is strong because its shape pushes down loads effectively.

1.5.3 Frames:

• Composed of beams and columns that are pinned or fixed.
• Extents in two or three dimensions.
• Its strength is derived from the moment interaction between beams and columns.

Frames consist of beams and columns connected in a way that allows them to interact. This interaction helps transfer loads across the structure, providing strength and stability. Frames can be used in both two-dimensional and three-dimensional designs, enhancing versatility.

Imagine a picture frame holding a photo. The frame (the structure) needs to be sturdy enough to hold the glass and photo and can sometimes be made to support heavier items. Similarly, in construction, frames support walls, floors, and roofs by allowing loads to be distributed and supported efficiently.

1.5.4 Surface Structures:

• Made from materials (flexible or rigid) having very small thickness compared to its other dimensions.
• They take several shapes like “thin plates” or “shells”.
• They support loads mainly in tension or compression with very little bending.
• Three-Dimensional.

Surface structures are characterized by their thin profiles relative to their lengths and widths. They can take on various forms, like domes or shells, and primarily support loads through tension or compression, minimizing bending stresses.

Think of a balloon. When you push down from the top, the sides bend outward but maintain their overall shape—this represents the tension in a surface structure. Alternatively, consider a dome atop a building, which uses its curved shape to distribute weight efficiently while maintaining minimal material use.

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