楼板结构早拆模板体系中早拆立柱可行性有限元研究

Finite Element Study on the Feasibility of Early Demolition of Columns in Early Demolition Formwork System of Floor Structure

为验证楼板结构早拆模板体系中立柱在混凝土强度达到设计强度的100%(养护龄期28 d)前还可再拆除,在考虑立柱的实际刚度,且在支撑楼板为弹性支座的假定下,运用ansys线性弹性分析模块,对拆除底模、主楞和次楞等构件后的施工阶段,仅由楼板和立柱组成的慢速时变结构,采用离散性时间冻结法,取出结构工作中的若干最不利状态(即各拆柱阶段)研究拆柱方法的可行性。结果表明:①对ansys模型中均匀布置的立柱间距从1. 3 m至1. 8 m,均得到楼板相同位置处的立柱轴力最小,拆柱位置即为轴力最小处的立柱;②选取5、7 d分别为第一、第二拆柱阶段,在拆除立柱后,得到拆柱前后立柱轴力增幅最大不超过20%,楼板第一主应力增幅最大不超过30%。结论:施工中应控制合理立柱间距和拆柱时间,并对楼板和立柱的应力、位移实时监测,才能保证拆柱后施工安全,实现立柱早拆。

In order to verify the slab structure,the columns in the early demolishing formwork system can be removed before the concrete strength reaches 100% of the design strength (28 days of concrete curing age).Considering the actual stiffness of the column and the elastic bearing of the supporting slab,using the ansys linear elastic analysis module,in the construction stage after the removal of the bottom mold,the main raft,the secondary raft and other components,in the slow time-varying structure consisting only of slabs and columns,the discrete time freezing method is adopted to take out some of the most unfavorable conditions in the structure work (i.e.,each stage of demolition) to study the feasibility of the method of demolition.Results show:①For the evenly arranged columns in the ansys model,the spacing between the columns is from 1.3 meters to 1.8 meters,and the axial force at the same position of the floor is the smallest.The position of the column to be removed is the column with the smallest axial force.②Day 5 and day 7 are selected as the first and second demolition stages respectively.After the column is removed,the axial force increase of the column before the demolition is not more than 20%,and the maximum increase of the first principal stress of the floor is not more than 30%.Conclusion: the reasonable column spacing and column removal time should be controlled during construction,and the stress and displacement of the floor and column should be monitored in real time to ensure the safety of the post-column construction and realize the early demolition of the column.