Frame is built with four steel rods. Frames shape is a square. In one point frame is connected to the ground by unmovable support. Frame is also connected to two additional unmovable supports by rods. In specific time on one of frame' side works higher temperature. As a result of higher temperature one of frame's rods had extended its length and thermal stresses appeared. Hooke's law will be applied to find reaction forces in frame. Frame's dimensions are known.