HF-joint is a high-strength bolted joint using HF-splice plates which have specially worked friction surface and thus enable a very high friction coefficient of over 1.2. The effective sectional area of the net section of connected members with the HF-joint was studied experimentally and the design procedure was shown. First, tensile loading tests were conducted to investigate the force transfer between a member and HF-splice plates by friction near the net section. From these results, the quantity of transferred force was made clear by using a function defined by a ratio of the strength of the gross section to the initial bolt tension. Then equations of the effective sectional area and the maximum strength of the net section were derived. Second, the design procedures in which the transferred force mentioned above was considered were shown for the following two conditions : 1) the gross section is made fully effective in elastic range, 2) no slip is made possible until a required strength is realized.