Development of Inspection System of Concrete Structure Damaged due to Large Displacement and Low Cycles Fatigue

利用教育、科学、体育和文化部的科研资助，对上述题目进行了三年的研究。结构的疲劳劣化分为两种情况。一种是由于大位移和低循环荷载引起的劣化，如地震。另一种是桥梁等结构在长期循环荷载作用下逐渐劣化。劣化与循环荷载水平密切相关。因此，为了评价结构的安全性和耐久性，循环荷载水平是研究结构劣化的重要因素。本文采用超声检测和声发射技术对循环荷载作用下的钢筋混凝土梁进行了研究。循环荷载水平由梁的静态弯曲强度的百分比决定。超声波谱法得到的RC梁的波谱响应幅值随着荷载循环次数的增加而逐渐减小。随着循环荷载水平的提高，其幅值呈快速下降的趋势。因此，频谱响应获得的超声能量随着载荷循环次数的增加而减小。另一方面，单位时间的声发射计数随着负载周期的增加而逐渐增加。随着循环荷载水平的提高，声发射计数有快速增加的趋势。自动对焦信号的幅值分布随载荷周期和循环载荷水平的变化而变化。结果表明，RC梁在疲劳过程中的频谱响应和单位时间声发射计数可以作为劣化的指标。超声声速随载荷循环次数的增加而减小。但超声速度的变化比声发射和光谱响应的变化要小。理论上，声发射的矩张量分析和SiGMA分析是由Ohtsu共同研究员开发的。采用矩张量分析对混凝土在荷载作用下产生的声发射事件进行分类。这些方法对阐明循环荷载作用下梁的断裂机理是有效的。利用模型梁进行了基于粘弹性理论的边界元分析，确定了谱响应的峰值频率和幅值。通过综合这些结果，确定了开发检测系统来评估遭受地震破坏和疲劳荷载循环的混凝土结构的劣化。少

By using a grant-in-aid for scientific research from the Ministry of Education, Science, Sports and Culture, studies have been conducted on the above-mentioned title for three years. Fatigue deterioration of structures are classified into two cases. One is the deterioration due to large displacement and low cycle loading, such as earthquakes. The other case is gradual deterioration subjected to cyclic loading for a long time such as bridge. There exists a close relationship between deterioration and cyclic load level. Therefore, to evaluate safety and durability of structures, cyclic load level is an important factor to investigate deterioration of structure.In this study, reinforced concrete (RC) beams under cyclic loading are investigated by the ultrasonic testing (UT) and the acoustic emission (AE). The cyclic load level is determined from the percentage to static bending strength of the beam. Amplitude of spectral response obtained from RC beam by the ultrasonic spectroscopy decrea … More se gradually with increase of load cycles. The amplitude show a tendency to decrease rapidly as higher as cyclic load level. Therefore, ultrasonic energy obtained by the spectral responses decrease with increase of load cycles. On the other hand, AE counts per unit time increase gradually according to increase of load cycles. The AE counts show a tendency to increase rapidly as higher as cyclic load level. The amplitude distributions of AF signal, are varied along with load cycles and cyclic load revel. The results show that spectral responses and AE count per unit time under fatigue process of RC beam could become an indicator of deterioration. Ultrasonic velocity also decrease with increase of load cycles. But variation of ultrasonic velocity is smoller than that of AE or spectral responses.Theoretically, moment tensor analysis and SiGMA analysis for AE are developed by a co-investigator Ohtsu. Moment tensor analysis is used to classify AE events generated in concrete under loading. These methods are effective to clarify the fracture mechanism of the beam under cyclic loading. BEM analysis based on the visco-elastic theory is also performed using a model beam, and peak frequency and amplitude of spectral response are confirmed.By combining together these results, it is confirmed to develop the inspection system to estimate deterioration of concrete structures suffered from earthquake damage and subjected to fatigue loading cycles. Less