Let's see if I can get the right. I have 12 cement columns which are three meters high (on third floor) and I want to put wooden columns on top of them 3 meters high. (fourth floor) The trusses will be on top of the wooden column. I'm concerned about how to connect the wooden columns to the cement columns so that they are stable and secure?
If the wooden columns are square and a standard size, use a bracket designed for deck construction. They are made of galvanized sheet steel and are bolted down to the concrete in the center. Look into an epoxy product (maybe 3M) that will allow you to use a stud to hold the steel bracket in the concrete. Often, cracks occur in a narrow column if an old fashioned lag anchor or lag type stud is used.
Are you sure they are cement and not fiberglass? Are they solid or hollow? You should maybe run the fourth floor joist out to the columns and put down some subfloor or decking material before adding the new columns. What are the diamiter of the 3rd floor columns? You need to determan the load bearing max on them. If they are fiberglass and 10 they should have a max load of around 10 thousand pounds per column. This should be ok. How far apart are the columns? This will also play into the wieght and how evenly it is distributed. Also check the load max on the new wood columns they will hold much less than the fiberglass.
