桩梁式托换技术有限元分析

Numerical analysis of underpinning structure composed of piles and beams

地铁施工穿越既有建筑物桩基础时,可采用桩梁式托换技术支撑上部结构和截除下方桩基础。运用ANSYS有限元程序中的"单元生死"技术,可对托换前、托换后和截桩三个托换工况下桩和框架柱的轴力变化以及变形特性进行数值分析。研究结果表明:被动托换是在桩截除时,托换荷载通过托换梁传递到托换桩,托换梁跨中的下挠会引起被托换框架柱轴力减少和邻近框架柱轴力增大;主动托换是在千斤顶的顶升过程中,托换荷载通过托换梁传递到托换桩,顶升过程中被托换处的各层框架柱轴力值增加,而邻近框架柱轴力减少;当顶升至被托换桩轴力为零再进行截桩,可保证截桩前后的托换体系轴力、变形不发生变化。主动托换桩顶沉降差与被动托换相比小得多。

When the subway traversed the pile foundations of existing buildings, the underpinning technology is applied to support the top structures and cut down the piles. The load transform law and deformation characteristic of underpinning structures can be analysed by using element bith and death technology of the ANSYS program. The loads of the top structures are transmitted to underpinning piles through underpinning beams in the process of piles cut down for passive underpinning; while, in the process of structure jacked up for active underpinning. The deformation of underpinning beams made axial force of supported pillars decrease and axial force beside pillars increase in passive underpinning, while axial force of supported pillars increase and axial force beside pillars decrease in active underpinning. When the axial force of pile jacked up reduces to zero, there are few changes of stress and deformation in the process of piles cut down. The differential settlement of pile top for active underpinning is less than that for passive underpinning.