What supports the 45-foot roof of the main factory building?

The support for a 45-foot roof in a main factory building is effectively provided by steel joist girders due to their structural properties. Steel joist girders are designed to span long distances while supporting significant loads, making them ideal for large spaces like factory buildings.

The use of steel adds strength and reduces the weight of the support system compared to other materials, which is crucial for maintaining stability and safety in a high-roof environment. These girders allow for fewer vertical supports and offer increased flexibility in the layout of the space underneath, accommodating machinery or equipment often used in factories.

In contrast, wooden beams may not provide the necessary strength and span for a roof of this height and often lack the durability required for industrial settings. Concrete columns, while strong, would require a more complicated arrangement and do not offer the horizontal support needed across large spans without additional bracing. Metal trusses are also strong but typically would be used in combination with other forms of support rather than solely supporting the entire roof structure by themselves. Thus, the unique properties of steel joist girders make them the most efficient choice for supporting the roof of the factory building.