Pile foundation reinforcing structure of existing building after seismic strengthening and reconstruction and construction method of pile foundation reinforcing structure

The invention discloses a pile foundation reinforcing structure of an existing building after seismic strengthening and transformation and a construction method of the pile foundation reinforcing structure. The pile foundation reinforcing structure comprises two prestressed reinforced concrete flat supports which are arranged in a crossed mode and a reinforcing straining beam which is used for reinforcing an energy dissipation substructure straining beam. The two prestressed reinforced concrete flat supports are horizontally arranged, and the axis formed by intersection is located on the center line of any existing bearing platform provided with the energy dissipation substructure column. The four end parts of the two prestressed reinforced concrete flat supports take the existing bearing platform located at the central position as a starting point, and on a building plane graph, the four end parts of the two prestressed reinforced concrete flat supports obliquely extend outwards to the other existing bearing