Effect of diaphragms on load distribution of prestressed concrete bridges

Load testing results for six prestressed concrete bridges were used to evaluate analytical methodologies. The bridges have different span lengths, number of lanes, and skew angles. Maximum strains and load distribution factors predicted by finite element analyses and AASHTO code specifications were compared with those from measurements. This comparison indicated that the diaphragm stiffness of the bridges examined is uncertain due to possible concrete cracking and weakness of the diaphragm-girder connection. Ignoring or considering low diaphragm stiffness gives better strain distributions across the bridge width than considering the full diaphragm stiffness, compared with the test measurements. Sensitivity study revealed that the diaphragm stiffness has significant effects on bridge strains and their distributions. It is important, though difficult, to choose a reasonable diaphragm stiffness in analytical analysis. Theoretically, full diaphragm stiffness can be achieved by posttensioning the diaphragm across the bridge width. If the full diaphragm stiffness does exist, the maximum strain and load distribution factor can be significantly reduced.