Members of the lateral load-resisting system consist of large metal or steel sections filled with or encased in concrete to increase their strength rather than for fire-protection only.
Sometimes this composite structural material or steel reinforced concrete (SRC) is used in conjunction with other materials like reinforced concrete or steel construction. For example, a SRC frame might be constructed above or below some reinforced concrete frame stories, or a building might contain both SRC and reinforced concrete or steel frames. In these situations one has to assess whether the SRC frames or members will define the seismic performance of the overall structure. If that is not the case then the other structural material should be selected.