I have a bearing wall in my basement I'd like to open up completely. Can I bolt a secondary 2x10 beam to it and toenail supports into the existing outer walls? It is a 15 foot span with no wall above it, but it does support all floor joists on that side. I can send a pics if necessary.

You should get a construction engineer to check what is needed. All bearing has to be on the sill and you will probably need a steel plate the length of existing beam

Chuck

I pretty much agree with Chuck. This must be a center wall, right? Depending on when it was built that wall is not load bearing but likely has a support column iniside it. Picture would ne nice