| Earthquakes occurred more frequently in recent years. The functionality of bridge structures during and after an earthquake is critical to the entire transportation system and economy. Studies have shown that abutments are prone to damage due to the excessive earth pressure caused by an earthquake,resulting in a bridge collapses and huge economic loss Research on the rational determination of the seismic-induced earth pressure(SIEP) on an abutments is deemed not complete. Currently in China, the conventional method for retaining walls is used to calculate the SIEP of an abutment. However, this is fundamentally incorrect as the mass and stiffness of the abutment are apparently greater than the retaining wall. Moreover, the abutment being a primary bridge component is connected with the bridge superstructure and as such it cannot move as freely as a retaining wall. So, in this study the important issue of SIEP on abutments is investigated. First, the Coulomb earth pressure theory is combined with the graphical method to determine the rupture angle in a soil wedge by considering the actual abutment geometry. And further to calculate the SIEP using a proposed method. Then, finite element analyses are performedutilizing ABAQUS software to numerically determine the SIEP, considering the abutment-superstructure interaction, and to assess the degree of the effects of the various system parameters on the SIEP. Details of this study are described as follows:1. Based on Coulomb earth pressure theory and Liang’s method about the partition of the soil mass behind an abutment, use a graphical technique method is proposed to obtain the rupture angle in a soil wedge and further to derive the calculation method for the SIEP of an abutment.2. The numerical models are carefully established followed by the detailed finite element analyses using ABAQUS software to determine the SIEP, where three levels of seismic waves, with the peak accelerations of 0.4g(strong), 0.2g(moderate), and 0.1g(small) are considered. The numerical results are compared with the theoretical ones.3. Based on the actual bridge data, with the consideration of abutment-superstructure interaction and the afore-mentioned three earthquake magnitudes, a numerical model is established to compute the SIEP. In this study,only the end span of a bridge is considered, namely no consideration of pier effects. The results with the consideration of the abutment-superstructure interaction are compared with those without such consideration.4. A sensitivity study is also carried out to evaluate the degree of the effects of the various system parameters on the SIEP. Based on the study results, the following are observed:(1) The active earth pressure coefficient(ka) is graduallyreduced with an increasing internal friction angle(φ), such reduction being more apparent for higher φ values;(2) ka also decreases with the increase of soil-wall friction angle(δ);(3) The decrease of ka is not so obvious when δ=φ/2~φ, while it becomes more apparent, when δ=0~φ/2;(4) With an increasing abutment back angle, ka gradually decrease; and(5) ka increases with the increase of horizontal seismic acceleration coefficient, but this effect is diminishing with higher φvalues. Among all system parameters, the internal friction angle’s change affects the earth pressure calculation result greater than the horizontal seismic acceleration’s change.5. In general, the effect of φ(internal friction angle) on the SIEP is larger than any other system parameter. It is also found in this limited study that the SIEP would be underestimated by more than 50% if the abutment-superstructure interaction is not taken into account, which would lead to an unsafe abutment design. In conclusion, the conventional method used to calculate the SIEP for retaining walls is not suitable to abutments. Instead, the approach proposed in this study is suggested, which considers all system parameters(particularly φ)and the important abutment-superstructure interaction effect. |
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