Parametric modelling of integral bridge spring reactions

Abstract

In integral type bridges, the soil’s interaction with the abutment and the piles (the structure) is usually modelled in practice using soil springs. The characteristics of these soil springs ultimately determine the structure’s response in terms of the applied bending moments, deflections and shears in the deck, abutment and piles(similarly for a bridge on footings). In this study, the influence on the soil-structure interaction (SSI) spring reactions in integral bridges was investigated. To this end, a series of parametrically varied 2D and 3D bridge models with soil springs were created and subsequently analysed. The parameters of span length, abutment height and soil condition for different percentages of live load and thermal expansion/contraction/gradient were considered and their influence on the SSI reactions was revealed through a series of parametric model testing. Both a piled foundation type and a footing foundation type were considered in the analysis work that was undertaken, and simplified models by authors such as Hambly (1991), Lehane (1999) and O’Brien and Keogh (1999) were assessed. The model test results showed that the maximum spring reactions (for abutments, piles and footings) followed either a linear relationship with increasing span or tended towards more non-linear type relationships. The results showed distinct and significant differences between the maximum spring reaction vs span relationships for the abutments and the piles (for the same bridge types). Further interpretation of the test results also showed that as spans increase (irrespective of the abutment height), the maximum spring reaction ratio (abutment/pile reaction ratio) tends towards unity.