A numerical study to compare trapezoidal and rectangular box girder bridges under moving vehicle loads

In the current study, CSI-Bridge finite element software is used to analyze two simply supported box girder bridge examples; rectangular and trapezoidal cross section. The box girders were different in depth, but the span length, cross section details, and material properties were constant. They were tested under HS20-44 AASHTO loading using a combination of live and dead loads in case of zero eccentricity (centrally placed). The findings showed that trapezoidal box girder bridges have the highest deflection, followed by rectangular box girder bridges. In more detail, as the depth increases by 33% to 66%, the deflection drops down by about 51% to 69% for rectangular, and by 40% to 49% for trapezoidal section. On the other hand, the trapezoidal girder experiences the highest longitudinal bending stresses along the span, whilst the rectangular girder experiences the lowest, when dead load and live load are combined (in the centre). That is to say, the longitudinal bending stresses decrease in the top flange by about 35% to 60% and 35% to 28% for rectangular and trapezoidal, respectively, while these stresses decrease, in the bottom flange, by about 35% to 69% and 34% to 52%, respectively, as the depth increases by 33% to 66%. Based on that, the rectangular section of the two components is considered to be the stiffest.