群桩效应对砂土地基中高桩承台群桩基础抗震性能的影响

Influence of group effect on the seismic performance of elevated pile-cap foundation in sand

针对我国广泛使用的高桩承台群桩基础,基于一组砂土地基中桩柱式基础的抗震试验数据和分析模型,建立了合理的高桩承台群桩基础Pushover分析有限元模型,分别研究在峰值和极限状态时,不同桩基自由长度和不同砂土密度条件下,群桩效应对高桩承台群桩基础整体峰值抗力和变形模式、桩顶水平剪力分配、桩身截面弯矩分布、桩身水平变形和曲率分布的影响,并讨论自由长度和砂土密度对群桩效应的影响。结果表明:群桩效应使基础峰值抗力降低;使峰值状态时承台和桩身水平位移增加,承台转角减小,而对极限状态时承台和桩身水平位移以及承台转角的影响主要依赖于自由长度大小;群桩效应对桩基剪力分配的影响较小;群桩效应对桩身分布弯矩峰值影响较小,但是对弯矩沿桩身的分布和桩身分布曲率峰值影响很大,且这种影响对于后排桩最大,中排桩次之,前排桩最小,自由长度和砂土密度对此时群桩效应的影响均较大。

The Pushover analytical FE models of elevated pile-cap foundation are built based on a seismic test and analytical models of shaft piles in sand. The influence of group effect （P-Multiplier） on the general seismic capacity of foundation, the shearing force distribution between pile heads, the forces and deformations distribution along piles, are studied in different aboveground heights and sand densities when the foundation is loaded into peak value state and ultimate state, respectively. The influence of aboveground height and sand density on group effect is also discussed. The results show that ： with group effect the lateral peak resistance is reduced ; the lateral displacement of the cap and piles at peak value state is increased, the rotation of the cap is reduced, and the impact level of the group effect on such variables at the ultimate state mainly depend on the aboveground height; the shearing force distribution is barely affected ; the peak values of the bending moment are influenced lightly, but the distribution of bending moments and the peak values of curvature are influenced seriously, especially for the trialing row piles; the group effect is significantly influenced by both the aboveground height and sand density.