Assuming you are referring to a table that would be used in a home and not a commercially made table, the answer to how strong the table is would depend on a few factors. The weight of the table would be one factor to consider. A table that is very lightweight is not going to be as strong as a table that is very heavy. The type of material the table is made out of is also going to be a factor. A table made out of a material like particle board is not going to be as strong as a table made out of a material like solid wood. The way the table is constructed is also going to play a role in how strong it is. A table that has legs that are bolted on is going to be stronger than a table that has legs that are just glued on. So, in answer to the question, how strong a table is on your shelf is going to depend on the weight of the table, the type of material it is made out of, and the way it is constructed.