When we tested it we had a problem trying to balance the books we put the books on top of the structure. I was surprised when we took off half of the structure and it held twice has much, it held 19 kg and the weight of the structure was 50g. We took the columns off the bad part and put them in the good part.
A big change was when we took off the half that was not strong. What we did with the leftover columns was added them to the good half.
I learned that lots of cylinder shapes work best. The shorter it is the stronger it is. The wider it is the stronger it is. Sometimes it helped to double up the columns.