What is the primary role of tension ribs in a counterfort wall?

The primary role of tension ribs in a counterfort wall is to resist flexure and overturning effects. Counterfort walls, which are a type of retaining wall, utilize these tension ribs to strengthen the wall structure against lateral earth pressures and any additional loads that may cause bending moments. The design of tension ribs provides additional support that allows the wall to withstand the forces acting on it, especially when there is a significant height difference in the retained material.

Flexure refers to the bending of the wall under load, and without adequate resistance, walls can fail by bending excessively. The tension ribs counteract these effects by providing a means to hold the wall together, effectively transferring the bending forces into the soil at the base and ensuring stability against overturning moments created by the weight of the retained earth and any surcharge loads. This is critically important in maintaining the integrity and safety of the structure.

The other options may serve their purposes in different contexts—enhancing aesthetics, distributing vertical loads, or improving drainage—but they are not the primary functions of tension ribs within the specific context of a counterfort wall. Focusing on the role of tension ribs highlights the structural engineering principles needed to maintain stability and safety in retaining wall design.