On the point in this daf, amud B, in which it is said that the miraculous middle bar bends through the corners, is there any commentary challenging this on the basis that the passukim in Shemos specifically call for 5 bars per wall, and thus 13 total would not fulfill the specifications? Or also challenging because the Western wall's center bar must reach to the Northern and Southern edges to fulfill edge to edge, and if it stops at the middle where it joined the longer middle bars they would not meet the specifications? But is the Northern (or Southern) middle bar really only 30 amos long? Shouldn't it be 30 1/2 amos to reach the center of the corner plank, or 31 amos to reach end to end to the Western external edge of the corner plank? If it serves a mechanical support purpose then the center bars should penetrate at least somewhat into the corner boards. But if the center hole is literally and precisely in the center then the bars should at least touch at a right angle within the corner planks, which might prevent them reaching the Western external edge.
Chaim, New England, USA
The Beraisa d'Meleches ha'Mishkan, which describes the construction of the Mishkan, indeed argues with the Gemara and states that there were 15 bars in all, with the central bar on each side measuring 30 Amos and the western bar measuring 12 Amos. Rashi (based on the Gemara) understands that the miraculous central bar can be viewed on each side as a separate bar but is in fact one bar, and this is the meaning of the verses in Terumah which describe 15 bars but also state that the central bar was one.
Your second question is raised by Rav Chaim Kanievsky shlit'a, who also quotes Bereishis Rabah (94:4) as stating that it was 32 Amos (see Etz Yosef ibid.). In this case, it would also pose a question on the length of the western bar, but Rav Kanievsky says that that bar would go through the other bar and thus would be 12 Amos. The Malbim and Ralbag suggest that the middle bar was not at the same height as the other middle bars on the western wall and therefore there were 12 Amos there as well as 30 Amos on each side. Apparently, this is also the view of Josephus in Antiquities.
Another answer is given for the Targum Yonasan who says that there was one bar of 70 Amos (instead of 72). Some opinions maintain that the extreme sides of the western wall were filed down and therefore there were only ten Amos on the wall itself.