Built-up hybrid composite box girders fabricated and tested in flexure

A new box girder has been fabricated using a pultruded hat-shape glass–fiber reinforced polymer (GFRP) trapezoidal section combined with a flat GFRP plate and a concrete slab cast above the plate. Both adhesive bond and shear stud systems were explored. The 3300 mm long simply supported girders were tested in positive and negative bending. Adding shear studs with the adhesive did not enhance flexural stiffness but increased flexural strength by 51%, relative to adhesive bonding only, by allowing flexural compression failure to be reached. The concrete slab thickness was designed to be fully in compression and contributed 87% and 112%, respectively, to flexural strength and stiffness of the girder. The new box girder was shown to have equivalent flexural strength to similar size, heavily reinforced, conventional concrete box girders of up to 2.5% steel reinforcement ratio.