基于声发射技术的混凝土梁桥弯剪受力状态下损伤试验

Experimental investigation of static damage of concrete beam under bending-shear based on acoustic emission technology

为实现使用声发射参数定量评估混凝土梁的损伤,开展了试件和构件层次的混凝土梁剪切试验研究。采用声发射技术对混凝土梁的损伤过程进行动态监测,总结基于声发射理论的混凝土损伤评估方法,并提出一种改进的损伤模型,采用三次多项式模型建立声发射参数与应力水平之间的定量关系,从而推导出混凝土梁的损伤演化方程,并计算出试件与构件对应于3种损伤模型的基于声发射技术的钢筋混凝土梁承载能力评估的损伤量。然后,通过与已有损伤模型的计算比较,验证损伤演化方程对混凝土梁损伤进行量化评价的有效性和准确性。试验结果表明:累计声发射数分三阶段变化,线性发展阶段的声发射信号较为活跃,相对应力水平位于0%～40%,其与材料本身含有较多微裂隙有关;而稳定增长阶段对应的累计声发射事件数与撞击数稳步增长,此时混凝土内部微裂纹稳定且缓慢发展,相对应力水平为40%～80%;在失稳阶段累计声发射数剧烈增加,其相对应力水平超过80%,试件内部裂缝达到失稳扩展状态。累计声发射事件曲线较好地描述了混凝土梁损伤发展变化的全过程,改进的损伤模型计算的损伤量在初始阶段发展较快,在中期趋于平缓,应力水平超过0.8以后损伤量发展迅速,直至试件破坏,能较好地反映混凝土梁损伤发展的三阶段变化规律。通过各损伤模型计算损伤度发现在相对应力水平较低时,试件或构件亦存在一定的损伤。

An experimental of a shear test of concrete beams at the specimen and component level was applied, to quantitative evaluate the damage based on the acoustic emission (AE) parameters. The damage process of a concrete beam was dynamically monitored using the AE technique. Concrete damage assessment techniques based on the characteristics of the AE theory were summarized, and an improved damage model was proposed. The quantitative relationship between the AE parameters and the stress level was established using a cubic polynomial model, and a damage evolution equation of concrete beam was developed. Then the validity and accuracy quantitative evaluation of concrete beam damage by damage evolution equation were verified, compared with the existing damage model. The results show that the AE cumulative number changes in three stages,the AE signal is active during the linear development stage, with a relative stress level of 0% to 40%, and that relate to the material contains many micro-cracks. The cumulative number of AE events and the impact number steadily increase during the stable growth phase. Further, the development of micro-cracks inside the concrete is stable and slow, with a relative stress level of 40% to 80%. The AE cumulative number drastically increases during the instability phase, where the relative stress level is over 80%, and the internal crack specimen reaches an unstable extended state. The AE cumulative event curve can better describes the entire damage process of a concrete beam, the amount of calculated damage quickly increases through the improved damage evolution model, tends to smooth at the mid-term stage, and increases rapidly when the stress level is over 0.8 until the specimen fails. The damage evolution model properly reflects the three stages of concrete damage development. The specimen or component is also damaged when the relative stress level is low, according to damage degree calculating through the damage model.