Unify

Apparently many don't know about this command
Use to combine discrete bits of line into a polyline - but remember ends of lines must join for them to be unified.

Steel sections>Complex profiles

Rather than use library parts for steel structure, consider complex profiles. When used with beams and columns it is a far more powerful modelling tool, as you can rotate, stretch, tilt beams and columns with far more ease and flexibility that library parts.
To get your steel shapes into your file, in AC15 there is a much easier way....

then

choose the ones you want and 'Add to Project'!