At least two longitudinal bars are arranged along the whole length of the beam. In the first and second class seismic design, the diameter of the bars shall not be less than 14mm, and shall not be less than 1/4 of the larger section area of the longitudinal bars at the top and bottom of the beam. In the third and fourth seismic design and non-seismic design, the diameter of reinforcement shall not be less than 12mm