Which girder type is less suited for significant spans exceeding 500 feet?

The two-girder design is less suited for significant spans exceeding 500 feet due to several factors related to structural efficiency and load distribution. In bridge engineering, the number of girders influences the load-carrying capacity and the capacity to resist deflections and vibrations.

When spanned over longer distances, such as 500 feet or more, a two-girder design may struggle to adequately distribute the loads and resist bending moments. This is because with only two girders, the distance between them requires that the girders themselves be larger and heavier to manage the loads, potentially resulting in increased deflection issues and challenging construction logistics.

In contrast, designs such as multi-girder and steel box-girder configurations provide a greater number of line supports, improving load distribution and structural integrity. Steel box-girders, for instance, are particularly well-suited for long spans because their closed shape enhances strength and stability while minimizing weight. Meanwhile, multi-girder designs allow for more effective load distribution across multiple members, thereby facilitating longer spans without excessive deflection or the need for overly large girders.

Overall, the limitations of the two-girder system in handling significant spans make it less favorable for designs in scenarios where long distances between