Method for modifying a single shaft combined cycle power plant comprising - a gas turbine part having a gas turbine stator and a gas turbine rotor supported by a thrust bearing and a loose bearing, - a steam turbine part having at least one steam turbine stator and a steam turbine rotor supported by two loose bearings, and - an intermediate shaft, which is rigidly connected to the gas turbine rotor and to the steam turbine rotor forming a rigid single shaft configuration, wherein the gas turbine stator is arranged on at least two pin-ended supports positioned at the cold side and on at least two pin-ended supports positioned at the hot side of the gas turbine part, and wherein several tie-rods are provided, whose first ends are connected to the gas turbine stator and whose second ends are held stationary with respect to the steam turbine stator, the method comprising the steps of - removing the gas turbine part, the pin-ended supports and the tie rods, - arranging at least one measuring device at the steam turbine part designed for measuring a physical dimension representing an axial displacement of the steam turbine rotor with respect to the at least one steam turbine stator caused by a thermal expansion of the intermediate shaft, - providing a new gas turbine part having a gas turbine stator, a gas turbine rotor supported by a thrust bearing and by a loose bearing, a hydraulic unit acting on the thrust bearing and a controller designed for controlling the hydraulic unit on the basis of data provided by the at least one measuring device, wherein the thrust bearing and the hydraulic unit are designed in such a manner that the axial position of the gas turbine rotor relative to the gas turbine stator can be steplessly shifted by means of the hydraulic unit within a predetermined range, - arranging the new gas turbine part on fixed supports positioned at its cold side and flexible supports positioned at its hot side, and - rigidly connecting the gas turbine rotor to the intermediate shaft. - a gas turbine part having a gas turbine stator and a gas turbine rotor supported by a thrust bearing and a loose bearing, - a steam turbine part having at least one steam turbine stator and a steam turbine rotor supported by two loose bearings, and - an intermediate shaft, which is rigidly connected to the gas turbine rotor and to the steam turbine rotor forming a rigid single shaft configuration, wherein the gas turbine stator is arranged on at least two pin-ended supports positioned at the cold side and on at least two pin-ended supports positioned at the hot side of the gas turbine part, and wherein several tie-rods are provided, whose first ends are connected to the gas turbine stator and whose second ends are held stationary with respect to the steam turbine stator, the method comprising the steps of - removing the gas turbine part, the pin-ended supports and the tie rods, - arranging at least one measuring device at the steam turbine part designed for measuring a physical dimension representing an axial displacement of the steam turbine rotor with respect to the at least one steam turbine stator caused by a thermal expansion of the intermediate shaft, - providing a new gas turbine part having a gas turbine stator, a gas turbine rotor supported by a thrust bearing and by a loose bearing, a hydraulic unit acting on the thrust bearing and a controller designed for controlling the hydraulic unit on the basis of data provided by the at least one measuring device, wherein the thrust bearing and the hydraulic unit are designed in such a manner that the axial position of the gas turbine rotor relative to the gas turbine stator can be steplessly shifted by means of the hydraulic unit within a predetermined range, - arranging the new gas turbine part on fixed supports positioned at its cold side and flexible supports positioned at its hot side, and - rigidly connecting the gas turbine rotor to the intermediate shaft.