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Mechanisms of Crack Propagation in Concrete and Control of Cracking

混凝土裂缝扩展机制及裂缝控制

基本信息

批准号：
60550337
负责人：
OHTSU Masayasu
金额：
$ 1.28万
依托单位：
Kumamoto University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1985
资助国家：
日本
起止时间：
1985 至 1986
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-60550337/
关键词：
Crack Stress Intensity Factor Acoustic Emission 境界要素法(BEM)

项目摘要

Mechanisms of crack propagation are investigated to control cracking in concrete. To clarify mechanisms of crack nucleation, a stress intensity factor in the linear elastic fracture mechanins was studied. A new method to determine a critical stress intensity factor is proposed. In experiments of notched beams, acoustic emission (AE) events were monitored, and critical load levels of frequent AE generation were determined. The stress intensity factor in a tested beam was analyzed numerically by the boundary element method (BEM), to take into account the exact notch configuration. From these AE observation and BEM analysis, the critical stress intensity factors of concrete materials were determined. Although the conventional critical values of the stress intensity factor were reported as dependent on specimen size and notch depth, obtained values are reasonably independent of them.A quantitative AE waveform analysis is investigated, on the basis of a generalized theory of AE which we previously proposed. The method developed can provide information on crack location, crack type, and crack orientation.To control cracking in existing concrete structures, a diagnostic method for cracks is proposed, which consists of the critical stress intensity factor, the AE waveform analysis, the ultrasonic spectroscopy, and AE characteristics in the core test. In the design phase, limit designs for controlling crack widths were investigated. Experiments on reinforced concrete beams with notches were carried out. Results confirm the applicability of limit designs proposed to control crack widths.

为控制混凝土裂缝，研究了裂缝扩展机理。为了阐明裂纹成核的机理，研究了线弹性断裂机制中的应力强度因子。提出了一种确定临界应力强度因子的新方法。在缺口梁实验中，监测了声发射事件，确定了频繁声发射产生的临界载荷水平。采用边界元法（BEM）对试验梁的应力强度因子进行了数值分析，并考虑了缺口的精确配置。通过声发射观测和边界元分析，确定了混凝土材料的临界应力强度因子。虽然传统的应力强度因子的临界值被报道为依赖于试样尺寸和缺口深度，但得到的值是合理的独立于它们。在我们先前提出的声发射广义理论的基础上，研究了定量的声发射波形分析。所开发的方法可以提供有关裂纹位置、裂纹类型和裂纹方向的信息。为了控制既有混凝土结构的裂缝，提出了一种由临界应力强度因子、声发射波形分析、超声波谱和岩心试验声发射特征组成的裂缝诊断方法。在设计阶段，研究了控制裂缝宽度的极限设计。对带缺口的钢筋混凝土梁进行了试验研究。结果证实了极限设计对控制裂缝宽度的适用性。