钢管混凝土脱粘机理及影响因素分析

Evaluation of the Mechanism and Influence Parameters of the Core Concrete Debonding in the Concrete-Filled Steel Tube

钢管混凝土结构结合了钢管与混凝土两种材料的结构力学特性,在高层建筑以及桥梁结构中得到了广泛应用。随着时间的推移,钢管与核心混凝土在应力和时间的作用下会出现包括弹性变形、徐变、混凝土收缩等问题。而由于材料的性质不同,最终导致钢管混凝土中的两种材料产生变形差进而导致脱粘,影响整体结构的服役性能。为了探究钢管混凝土在服役周期中脱粘的估算方法,通过分别计算核心混凝土与钢管的变形得出脱粘量,并与深圳赛格广场大厦(简称赛格大厦)的钢管混凝土脱粘的测量值进行对比,探索计算模型对钢管混凝土脱粘估算的适用度与精确度。在钢管混凝土中,径向变形主要分为核心混凝土的收缩形变、泊松形变与徐变形变以及钢管的泊松形变与徐变形变。由于钢管混凝土结构的密封性,假设钢管内恒温恒湿。在此基础上,采用较为普遍使用的混凝土规范ACI 209R-92与CEB-FIP为计算模型,以赛格大厦建成至检测日期为计算时长、设计荷载及自重为应力条件,计算混凝土的收缩、泊松与徐变形变;对钢管进行受力分析,结合材料性质计算相应变形。计算中,以对脱粘量增长有利的方向为正方向,以不同变形之和作为钢管混凝土的脱粘量。结果表明:相较于ACI模型,CEB-FIP的计算结果与实测值更为接近。特别的,CEB-FIP模型对核心混凝土收缩的估算普遍大于ACI模型;在徐变量上,ACI模型受尺寸影响较大,徐变计算量小于CEB-FIP模型。赛格大厦钢管混凝土中同时采用了通过振捣密实的传统混凝土与自密实混凝土。相较于传统混凝土,自密实混凝土会发生较大的收缩变形,该情况能较好地体现在两种模型的结果中,且CEB-FIP的结果与其模型描述中较为接近;实测值显示,核心混凝土脱粘自上而下呈“小—大—小”分布,CEB-FIP的计算与该趋势相符,而ACI结果则呈现自上而下递减的趋势。

The concrete-filled steel tube(CFST)combines the structural and mechanical properties of both steel pipe and concrete and are widely used in high-rise buildings as well as bridge structures.Over time,the steel pipe and the core concrete will deform,including elastic deformation,creep,and concrete shrinkage.Due to the material difference of the concrete and steel,the deformation difference between the two materials in steel pipe and concrete eventually leads to debonding,which affects the service performance of the overall structure.In order to investigate the estimation method of debonding of CFST in service life,this paper explored the applicability and accuracy of the calculation model for estimating debonding of CFST by calculating the deformation of core concrete and steel pipe separately and deriving the amount of debonding and comparing it with the measured values of it in Shenzhen Saige Plaza Building.In CFST,the radial deformation is mainly divided into two parts:the shrinkage,Poisson deformation and creep of the core concrete,and Poisson deformation and creep for the steel tubes.Due to the hermetic condition,a constant temperature and humidity was assumed inside the steel pipe.On this basis,two commonly used concrete code ACI 209 R-92 and CEB-FIP were adopted in this work.And the shrinkage,Poisson’s and creep of the concrete were calculated with the calculation time from the completion date of the building to the testing date,and the design load and self-weight as the stress conditions.The steel pipe was analyzed for stress and the corresponding deformation was calculated with the material mechanics.The sum of different deformations was calculated as the amount of debonding in the CFST with the positive direction of debonding growth.The results show that the calculated values of CEB-FIP are closer to the measured ones compared to the ACI model.In particular,the estimation of shrinkage of core concrete by CEB-FIP model is generally larger than that of ACI model;in terms of creep variation,ACI model is more influenced by size of the concrete and the amount of creep is smaller than that of CEB-FIP model.Both conventional concrete compacted by pounding and self-compacting concrete were used in the CFST of Saige Tower.Compared with the conventional concrete,the self-compacting concrete undergoes larger shrinkage deformation,which is well reflected in the results of both models,and the results of CEB-FIP are closer to its described in the manual.The measured values show a"small-large-small"distribution of core concrete debonding from top to bottom,and the CEB-FIP calculation is consistent with this trend,while the ACI results show a decreasing trend from top to bottom.