The structure and the construction method which are changed in nothing ballast plate girder bridge to a ballast steel composition reinforced concrete slab bridge

A structure and a construction method for changing a plate girder bridge without ballast to a ballast steel composition reinforced concrete slab bridge are provided to reduce the construction cost by using high speed hardening concrete characteristics and reaching the concrete to the design strength in a short time. A steel plate is welded or bolted on a lower flange of a plate girder. Brackets are welded or bolted at the area where the lower flange and a web are met. Reinforcing bars are distributed in the brackets. The steel composite reinforced concrete girder is formed by pouring and hardening the first high speed hardening concrete. Sleepers and rails are removed from the plate girder. The plate girder is cut. Reinforcing bars are distributed to a rectangular direction of a bridge axis. The steel composite reinforced concrete slab bridge is formed by pouring and hardening the second speed hardening concrete up to the upper ends of the brackets. Pebbles are laid to form ballasts. The sleepers are horizontally placed on the ballasts. The rails are fixed to the sleepers.