what are girder truss
A truss is a roof or floor support structure built from a connected series of box- or triangle-shaped elements to distribute load to a building's walls or foundation. These are often pre-fabricated and sent to a construction site. A girder truss is designed to support other secondary roof supports. Buildings constructed in L or T shapes use girder truss systems where the roof changes direction. Using these structures in roof design eliminates the need for a load-bearing wall below, resulting in open floor plans.