A parametric study, using the FEM-software package ABAQUS, validated on experimental results found by Abspoel, was conducted on S690 steel plate girders to address if the results of the previous researches was valid. Using a slightly different analytical model the results show the maximum web slenderness of this steel grade in both 6000 mm2 and 12000mm2 was the same. It was shown that the maximum bending moment was found when the top flange was able to yield, shortly followed by sudden collapse. A new parametric study, to expend the optimizing plate girders using S890 steel was conducted as well to address the usefulness of steels with higher yield strength in plate girders subjected to bending. This study again used the geometry used by Abspoel. The results showed a decrease in maximum web slenderness, but still a significant increase in bending moment capacity compared to the S690 plate girders. It was shown that using an optimized S890 plate girders compared to hot rolled section made also from S890 steel, could reduce the use of steel by more than 80%. After the parametric studies showed increasing capacity, the geometry used to numerically model the plate girders, was critically addressed, using small scale numerical studies using FEM-software. These tests showed that not only the slenderness of the web was a factor in the bending moment capacity of a plate girder, but also the flange geometry plays a significant role. It was shown that increasing the length of the tested part of the girder, the failure mode could change from flange yielding to an instable mode in which the flange rotated around its longitudinal axis, resulting in a much lower bending moment capacity. An extra investigation in using a hybrid steel composition resulted in showing the potential of this optimization. Because by adding lower grade steel, more ductility was shown due to these parts yielding prior to yielding of the compressive flange, resulting in possible safer design.

The research concentrated on a behavior of the deep composite deck ComFlor210 under a concentrated force. The distribution of a concentrated force in ComFlor210 was studied numerically and analytically. The finite element model of a composite slab with 5.4m span showed good agreement with test results in the elastic stage. The parametric study of composite slab ComFlor210 revealed that in a slab with span 3.2m and 5.4m the load is distributed over three middle ribs. In a slab with 7.2m span, the load was spread over all five ribs. The bending resistance of the rib was exceeded for slab with 7.2m span. In the elastic part of the load-deflection curve, the variation in cross-sectional properties causes a minor change in a slab response. The proposed engineering model was unable to predict the deflection of the composite slab under concentrated load with the desired accuracy.