Bridges

The full span construction method is one of the most commonly used methods in the construction of precast segmental bridges in recent years. In this method the precast segments are first lifted into place and then stressed together by prestressing tendons to form a complete bridge span. These prestressing tendons can be either internally bonded or externally unbonded to the concrete section.

Generally, the internally bonded tendons are more structurally efficient because these tendons will elongate together with the surrounding concrete due to strain compatibility when the bridge span is under external loading. However, the use of internally bonded tendons requires careful localised reinforcement detailing, in particulars in the anchorage zones, which will translate into additional construction efforts. In addition, if the internal tendons are subjected to durability problems during the bridge service life, they would be difficult to be repaired or replaced. The aforementioned challenges have led to an increasing interest in the use of externally unbonded tendons, which will make the inspection, restressing and replacing of tendons feasible and easier.

This paper presents a parametric study which compares of the amount of prestressing required for two similar precast segmental bridge spans, one with internally bonded tendons and the other with externally unbonded tendons. Through the comparison of the prestressing tendon quantity, this study aims to determine a range of span-to-depth ratio, where the use of external tendons will become more cost effective and does not significantly increase the cost of the structure.