砖混结构混凝土现浇板收缩裂缝的数值分析

NUMERICAL ANALYSIS ON SHRINKAGE CRACKS OF CONCRETE CAST SLAB IN BRICK AND CONCRETE STRUCTURE

运用ANSYS有限元软件,建立三维有限元模型对一个纵向8个开间、横向2间进深的砖混结构多跨连续板收缩裂缝进行数值分析。现浇板的收缩作用是通过对板施加当量温差实现的。数值计算后,在后处理程序中可查看现浇板的应力云图,用路径操作的方法可以得到现浇板的纵向和横向第一主应力-位置曲线。现浇板混凝土收缩产生的最大拉应力主要分布在板的4个大角,以及墙体和现浇板的边界处,板跨中处较小。沿着现浇板的纵向,从端部房间到中部房间拉应力逐步增大,增大率只有5%―7%。现浇板的纵向和横向拉应力相差不大。现浇板跨中无穿线管时,最大应力出现在墙体和现浇板的边界处;而跨中设置了穿线管后,跨中出现了明显的应力集中,这成为穿线管处易出现收缩裂缝的主要原因。现浇板收缩应力的大小,取决于楼层墙体侧移刚度,墙体侧移刚度与墙体的水平截面面积成正比。增大墙体间距,能够减小墙体侧移刚度,从而减小现浇板收缩应力的水平。

A three-dimensional finite element model was established using finite element software ANSYS.The numerical analysis on shrinkage cracks of a multi-span continuous concrete slab was conducted using the finite element model.The cast slab had 8 compartments in the longitudinal direction and 2 depths in the transverse direction.The shrinkage action of the cast slab was simulated by an equivalent temperature difference method.After a numerical calculation,the stress contour plot of the cast slab could be checked in the post-processor.The relation curves between first principle stress and the location of the longitudinal and transverse directions could be gained by the path operation method.The biggest tension stress caused by concrete shrinkage of the cast slab mainly located in the four corners and the boundaries between the wall and the slab,and the tension stress was little in the middle of the slab.Along the longitudinal direction of the slab,the tension stress caused by concrete shrinkage became bigger from an end room to a central room,and the increasing rates were from 5 percent to 7 percent.The difference of the tension stress between the longitudinal and transverse directions of the slab was small.The maximum tension stress appeared at the boundaries between the wall and the cast slab when there was no thread tube in the middle part of the slab.Because there was stress concentration phenomena due to the existence of a thread tube,the shrinkage cracks appeared at places.The shrinkage stress depended on the lateral rigidity of the walls which was direct proportional to the crossing area of the walls.The lateral rigidity of the walls could be reduced with the increasing of space.Therefore,the level of the shrinkage stress could be reduced by increasing cross-wall space.