钻孔灌注桩钢筋笼上浮机理分析

Analysis on mechanism of reinforcing steel cage floating based on cast-in-place pile

为研究钢筋笼上浮机理,根据相似理论研制出能够模拟新拌混凝土性能的相似混凝土.基于相似混凝土,开展了薄铁片、钢筋和箍筋的提拉试验,分别得到薄铁片的侧阻力、主筋的端头阻力和箍筋阻力的计算模型,总结了各因素对阻力的影响规律.结果表明,混凝土与钢筋之间的相对运动速度对侧阻力、端头阻力和箍筋阻力影响不大;侧阻力峰值与侧面积和埋深呈线性关系,侧阻力由摩擦力和侧粘力两部分构成;钢筋端头阻力峰值与端头受到的混凝土压力成正比.箍筋阻力是箍筋排开混凝土时受到的竖向合力,峰值与箍筋上表面积和混凝土压强乘积成正比.分析表明混凝土液面进入钢筋笼而混凝土导管口位于钢筋笼底部以下时,钢筋笼最容易发生上浮,建立了这种情况下钢筋笼受到的向上合力计算方法,分析了向上合力与主筋根数、箍筋间距、混凝土在钢筋笼内的高度的关系.

In order to study the floating mechanism of reinforcing cage,the similar concrete which can simulate the performance of fresh concrete is developed based on the similarity theory.Based on similar concrete,the tension tests of thin iron sheet,steel bar and stirrup are carried out.The calculation models of side resistance of thin iron sheet,end resistance of main reinforcement and stirrup resistance are obtained respectively,and the influence rules of each factor on resistance are summarized.The results show that the relative velocity between concrete and steel bars has little effect on the side resistance,end resistance and stirrup resistance;the peak value of side resistance is linearly related to the side area and buried depth,and the side resistance is composed of friction force and side viscous force;the peak value of resistance at the end of steel bars is proportional to the concrete pressure at the end.The stirrup resistance is the vertical resultant force when the stirrups are placed in the concrete.The peak value is proportional to the product of the surface area of the stirrups and the concrete pressure.The analysis shows that when concrete liquid level enters the reinforcing steel cage and concrete conduit mouth is below the bottom of the reinforcing steel cage,the reinforcing steel cage is most likely to float.The calculation method of the upward resultant force of the reinforcing steel cage is established.The relationship between the upward resultant force and the number of main reinforcement,the spacing of stirrups and the height of concrete in the reinforcing steel are analyzed.