The determination of cell numbers in concrete box girder bridges is a crucial aspect of design, balancing structural efficiency with load distribution considerations. Engineers typically adhere to established guidelines, considering the relationship between the bridge’s depth and width.
A general rule of thumb suggests that if the bridge depth exceeds 1/6 or 1/5 of the total width, a single-cell configuration is recommended. This is because deeper girders exhibit greater inherent torsional stiffness, negating the need for additional cells to manage transverse loads.
Conversely, when the bridge depth is less than 1/6 of the width, a twin-cell or multiple-cell design becomes preferable. As highlighted by Jorg Schlaich and Hartmut Scheef (1982), this configuration enhances transverse load distribution, ensuring a more balanced stress distribution throughout the structure.
However, even in cases of wide bridges with relatively shallow depths, engineers are advised to exercise restraint in increasing cell numbers. This is because the marginal improvement in transverse load distribution diminishes as the number of cells exceeds three. In essence, adding more cells beyond this point may not justify the added complexity and cost of construction.
Therefore, the optimal number of cells for a concrete box girder bridge is a function of its depth-to-width ratio and the desired balance between structural efficiency and load distribution. By adhering to established guidelines and considering the specific requirements of each project, engineers can make informed decisions that ensure both safety and cost-effectiveness.