Experimental Study of Post-Tensioned Steel Trusses with Composite Slabs

Test specimen No. 1, with a simple bridge span of 8534 mm, consisted of a 150 mm thick, high performance concrete deck in composition with a 600 mm deep steel truss. The composite system also included two12.7 mm tendons extending from end to end of the structure and draped at the third points above which equal test loads were applied. Prestressing levels of 460MPa, 690MPa and 920MPa provided mid-span pre-cambers of 1.8mm, 3.3mm and 4.4mm, respectively. For the extra 7.9% of the tendon cross sectional area as compared to the bottom chord cross sectional area, the post-tensioned composite truss resisted a maximum total load of 670kN which was 20.4% higher than the total load of 568kN in the case of a composite truss without prestressing. However, for similar specimen No. 2 with no composite slab, the use of post-tensioned tendons had no advantage on the steel non-composite truss because the specimen critically failed in the buckling mode of the top chord.