Which assembly forms a rigid framework of triangular shapes in construction?

The assembly that forms a rigid framework of triangular shapes in construction is trusses. Trusses are specifically designed to distribute weight and provide stability, making them ideal for spanning long distances without needing support pillars in between. Their triangular design is significant because triangles are inherently strong shapes; they do not bend or warp when weight is applied evenly across their structure.

In construction, trusses are often used in roofs and bridges, providing an efficient solution to support loads while minimizing the amount of material needed. Their ability to maintain structural integrity under various loads makes them a fundamental component in modern building design.

Other assemblies like beams, rafters, and joists have different functions; for example, beams are typically horizontal supports, rafters are sloped members that support roof coverings, and joists are horizontal supports for ceilings or floors. However, trusses specifically utilize a framework of interconnected triangles, which is why they are the correct choice in this context.