The deal was struck last week when Builders Beams briefly went into administration but was immediately sold by Grant Thornton.
Steelo has grown rapidly from its origins as a one-man venture founded by CEO Michael Krajewski.
Krajewski said: “This is the first step of a greater plan, which is to build a group of companies that will provide an exceptional service in the steel industry.
“Following the acquisition, the focus will be on making Builders Beams great again, preserving the heritage and long-lasting relationships with the client base built over the years.”