Bridge pile skeletons, footings and piles were significantly reinforced against large-scale earthquakes after the Great Hanshin Earthquake. As a result, the volume of reinforcing bars and their diameter have substantially increased, particularly in the case of cast-in-place reinforced concrete piles (RC piles), which has pushed up construction costs. To combat this, it is necessary to develop suitable and economical cast-in-place RC piles featuring high earthquake resistance.
   To this end, the RTRI proposed a new structure to connect the RC pile head with the footing. The structure would remain intact in L1 level earthquakes and suppress damage after yielding in L2 level earthquakes (Fig. 1). With the increased volume and smaller hoop tie intervals, it prevents buckling and failure in the main reinforcing bars and protects the internal concrete. The adhesive sheet wrapped around the pile head is to prevent the corrosion of damaged reinforcing bars.
   A horizontal model-loading test demonstrated that the structural performance outlined above is attained with the high-density hoop ties at the pile head (Fig. 2). The RTRI also proposed a method of evaluating the deformation characteristics of the structure and created a design program and a manual. Calculations showed that the costs of pile-hammering operation would be cut by 10 to 20% due to the reduced diameter and volume of the main reinforcing bars in the RC piles.