Hydrodynamic added mass on a four-pile elevated pile-cap foundation and its impact on seismic structural response

The pile-cap foundations, serve as the supporting structures for cross-sea bridges and are frequently subject to seismic action in service. The analysis of the hydrodynamic added mass is crucial for evaluating the dynamic characteristics and seismic response. This paper investigates the hydrodynamic added mass of submerged four-pile elevated pile-cap foundations. A comparative analysis with isolated cap and pile group models is conducted to quantify the effect of pile group – cap interaction on the hydrodynamic added mass under various influencing factors. The results show that the interaction can increase the added mass of the pile-cap foundation. The amplification effect is most pronounced near the bottom of the cap and the pile top, with local maximum increases reaching up to approximately 24% and 23%, respectively. The maximum increase in the total added mass for cap and piles can reach up to about 20% and 4%, respectively. However, the average absolute value of the influence coefficient of the interaction on the peak seismic response for the four-pile elevated pile-cap foundation is below 0.5%, with a maximum of approximately 2% under the specific parametric ranges and superstructure masses in this study.