What type of stress do pre-stressing tendons help to balance in a concrete member?

Pre-stressing tendons are used in the design of concrete members to counteract tensile stress. In concrete structures, tensile stress is a major concern because concrete is relatively weak in tension. When a load is applied to a concrete member, it tends to bend, creating tensile forces on the bottom side (in a simply supported beam, for instance) and compressive forces on the top.

By introducing pre-stressing tendons, which are typically high-strength steel cables or bars, into the concrete before it is subjected to service loads, these tendons can be tensioned. This pre-tensioning creates an initial compressive stress in the concrete, effectively balancing out the tensile stresses that occur when the structure is loaded. This method helps to ensure that the concrete remains in compression rather than tension, which enhances the member's overall performance and durability.

The other types of stress listed, such as compressive stress, cyclic stress, and shear stress, do not directly relate to the primary function of pre-stressing tendons, which is to address the vulnerabilities of concrete under tensile loading conditions.