Using the strong connection factors and the pre-established position of the plastic hinges of framed beam given in JGJ 99-2015, the strength demand on the column face is derived, from which the upper limit of the length of the cover plate is determined, and the required area of the cover plates is computed. An example shows that when the frame column using rectangular steel tube, the required area is about 25%-30% of the flange area of the beam. For short beams, the code-specified strong joint factor of JGJ 99-2015 is not great enough, the paper presented a equation to compute required strong joint factor higher than that of JGJ 99-2015.