Influence of Compressive Strength on Ultimate Strength of Composite Concrete-Steel Girder Subjected to External Prestress

Experimental programmed was carried out to investigate the influence of compressive strength on composite steel I-girder decks subjected to external prestress. This program included fabricating and testing six scale down 1/4, were designed according to AASHTO LRFD 2012 standard specification. Each girder was test as simply supported with span of 3.90m and classified in three groups. The first group consists of two girders for which the concrete strength is 50 MPa. The second group consists of two girders for which the concrete strength is 70 MPa. The third group consists of two girders for which the concrete strength is 90 MPa. In all groups, the first girder has straight eccentricity without deviator and the second girder have inclined variable eccentricity with deviator at the mid span. The applied loaded incrementally up to failure under the action of two point loads for each increment of load. Vertical deflections were measurement at mid and under point load. The prestressing force in the all girders was (9) Ton applied after the applied of superimposed dead load on RC deck slab. The variables included the compressive strength of concrete, the values of the eccentricity which mean that (location of prestress below bottom face) and with or without deviator. The girders of group (1) showed ultimate load of 210 and 230. The girders of group 2 showed ultimate load of 260 and 280. The girders of group 3 showed ultimate load of 300 and 320. When the compressive strength of concrete is increased from 50 MPa to 90 MPa it causes increased the ultimate load about 42.85 %. In general the ultimate load increase by 10 % when the compressive strength increases 10 MPa.