There are about 70 prestressed concrete T-beam girder bridges built between 1953 and 1970 in the Netherlands. Ensuring the safety of these existing bridges under current traffic conditions is
imperative. Upon initial assessment of these existing prestressed concrete T-girder bridges, half of them didn’t meet the safety requirement specified by the design code even though they didn’t show any sign of distress during inspection. This is because the system behaviour of the T-girder bridges (i.e.) load transfer mechanisms such as CMA (compressive Membrane Action) and load redistribution were not considered, which could potentially increase the calculated strength capacity of these existing bridges. Therefore, a computationally efficient method for evaluating these bridges is needed.
This research addresses the challenge of accurately predicting the strength capacity of prestressed concrete T-girder bridges using a computationally efficient approach. The study involves modelling the 2D bridge deck in the horizontal plane using orthotropic plate elements and 2D individual girders in the vertical plane with non-linear material properties. The 2D bridge model was compared with a 3D linear bridge deck model, showing a variation in bending moment between 10% to 13%, sufficient for studying load effects. The 2D individual girder model built was validated using experimental data of the disconnected T-beam test of the Vecht Bridge, incorporating a quasi-Newton solution method with the Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm. The predicted load versus deflection curve from the 2D non-linear individual girder model closely followed the load versus deflection curve obtained from the experimental test results. To combine the 2D bridge deck model with the 2D non-linear individual girder model, an equivalent loading technique was developed by numerically solving the shear force distribution of the critical girder in the 2D bridge deck model. The staggered 2D Non-Linear Finite Element Approach developed utilising the equivalent loading technique accurately predicted the ultimate failure load of the connected T-beams (system behavior) within 10% of experimental values, despite neglecting the effect of end crossbeams. The 2D bridge deck model without considering crossbeam effects showed conservative stiffness estimates. Crossbeam inclusion in the model indicated significant improvements in stiffness, load distribution and redistribution. The 3D non-linear finite element model predicted 87% to 95% of the failure load of the connected T-beam tests [10]. The 2D non-linear individual girder model using the staggered non-linear approach predicted up to 96.5% of the ultimate failure load of the connected T-beam test, achieving this with a run time of approximately 18 to 21 minutes. Overall, the staggered 2D Non-Linear Finite Element Approach developed shows promise for preliminary bridge safety assessments offering a balance between computational efficiency and accurate prediction of strength capacity.