Impact of pile head restraint and soil stiffness on the response of steel piles for integral abutment bridges

Sammanfattning

Integral abutment bridges are commonly designed using simplified pile models wherethe pile is treated as an isolated structural element with a free pile head. To betterrepresent the actual structural behaviour, global buckling analysis can be used as analternative modelling approach, where stabilisation from the surrounding soil andthe integrated bridge system is considered. The purpose of this study is thereforeto evaluate whether alternative modelling approaches can provide a more realisticestimation of axial pile capacity in integral abutment bridges.The study combines literature review, case study and finite element modelling. Afinite element model was developed in BRIGADE/Plus and verified against handcalculations using simplified single pile models. The analyses were gradually extended to include soil resistance, transverse loading, and different boundary conditions. Both single piles and piles integrated into the bridge system were analysedunder two different soil conditions to evaluate force distribution, bending moments,buckling behaviour, and pile capacity.The results show significant differences in structural behaviour depending on soilconditions and model assumptions. The piles embedded in friction soil developeda higher axial capacity than the piles surrounded by soft clay. Compared with theisolated pile models, the piles integrated into the bridge system generally exhibitedan increased capacity due to redistribution of internal forces and the sequential formation of plastic hinges. The results also indicate that simplified assumptions withfree pile heads may underestimate the stabilising effect provided by the surroundingstructural system.The study demonstrates that modelling assumptions regarding soil stiffness andpile restraint significantly influence the predicted pile capacity in integral abutmentbridges. Simplified single pile models may therefore underestimate the structuralcapacity of piles interacting with the bridge system. The results indicate that soilstructure interaction and restrained pile behaviour should be considered in nonlinear analyses of integral abutment bridges, particularly when evaluating ultimatelimit states and buckling behaviour.