地下室增层截桩次生内力研究——以三桩一柱承台为例

RESEARCH ON SECONDARY INTERNAL FORCES CAUSED BY PILES CUTTING-OFF IN BASEMENT STORY-ADDING: A CASE STUDY OF PILE CAP SUPPORTED BY THREE PILES AND A COLUMN

地下室向下增层中常涉及截桩托换,截桩施工时控制结构内力变化对结构安全至关重要。为研究截桩对新增下柱内力的影响,以正三角形三桩一柱承台为例,采用解析方法推导了下柱顶截面在不同截桩顺序下的内力增量系数,以及组合变形条件下内力增量的计算方法。分析结果表明：解析式计算结果与有限元分析结果相吻合,而截桩顺序分析说明下柱顶内力增量与上柱底荷载和截桩顺序有关。在实际工程中应合理地选择截桩顺序,以保证工程的安全。

Basement story-adding usually involves such underpinning construction procedures as piles cutting-off. In the process of piles cutting-off controlling internal forces variation of newly constructed structure has significant meaning to building safety. In order to estimate the influence on internal forces of newly constructed lower column,a regular triangle pile cap supported by three piles was considered as an example. Increment coefficients of internal force on top cross section of the lower column were deduced by analytic method considering different pile cutting sequences,and the internal force increments were calculated under combined deformation conditions. The case study indicated that the results obtained by the analytical method were consistent with FE method results. Moreover,it indicated that the internal force increments of the lower column were related to bottom cross section loads of upper column and piles cutting-off sequences. As a conclusion,it was suggested to select a reasonable pile cutting sequence to ensure the safety of engineering.