Struggle
The column should no be weakened as long as the recess is not within the column and the anchorage is fully grouted and column concrete strength is the same as grout strength, so about 40MPa! The main problem is the reinforcement placement and fitting it all together.
RE Multi/Mono strand, how many strands are we talking about and what duct and anchorage type.
PS I am getting sick and tired of incomplete questions on this site. We are all engineers, how about we put our brains into gear. We cannot answer questions sensibly without adequate information! If you do not know how much information you need to supply, you should not be working in the area and asking the question!
Single strand stressing with round duct does not work. The strands become interwoven and you have no idea how much friction you will get, so you have no idea how much force you will get into the strands. The first will be ok, the last will get very little for large tendons. In fact the last strands will put extra load into the first strands!
As an example of what happens we once stressed 42 strand tendons as multi-strand to 82.5% load and some strands started failing (idiot concrete contractors fault fortunately) so we had to de-tension then, and you have to do that strand by strand. These tendons were 100m long so expected extension of about 600-700mm. When we released the load on the first strand, it pulled in about 10mm and stopped, with no load at the end! It was purely held at nearly fill load by friction with the other strands!
