How to get Additonal strength bonus dmg on weapon?

By putting points into strenght, the more strenght you have the more will be the bonus, i just dont know the limit for that bonus.
Also i think this kind of question should be posted here:
viewtopic.php?f=4&t=124&start=22750

Not sure if thats what you are asking but there are some items that grant additional strength damage bonus like candlewake/shroud royal/lazhruk's round shot mo, etc. You can search for them in documentation.