Established in 2005, GSI specialises in the design, fabrication and erection of structural steel.
The company has production facilities in Hamriyah Free Zone and is capable of delivering 24,000 tonnes a year of structural steel products.
The deal is the latest by Arabtec aimed at controlling its supply chain.
In 2005 the contractor bought Austrian Arabian ready mix, and at the end of last year it bought Abu Dhabi-based Target Engineering Construction Company which will give a marine works capability.
It has also developed its own mechanical and electrical expertise.