粉煤灰对受弯开裂钢筋混凝土内氯离子侵蚀的影响

为了研究粉煤灰掺量对受弯开裂钢筋混凝土中氯离子侵蚀过程的影响,采用三点受弯的方法将粉煤灰掺量(质量分数)分别为0%,15%和30%的混凝土梁进行两两自锚,并将不同开裂状态下的试验梁放置于5%(质量分数)的NaCl溶液中进行干湿循环侵蚀试验.结果表明：干湿循环作用下,受弯开裂混凝土的表层对流区深度在10~20mm,且随着裂缝宽度的增加,对流区深度逐渐增大;混凝土的氯离子渗透性能随着弯曲裂缝宽度的增大而提高;粉煤灰掺量在15%以上时能有效改善开裂混凝土的抗氯离子渗透性能,其等效氯离子扩散系数是普通混凝土的1/8~1/6;扩散分析时,混凝土损伤劣化效应系数K与裂缝宽度w,粉煤灰掺量f可用指数关系进行拟合.     

基于预估器的一类多智能体系统神经动态面输出一致控制

本文针对一类含未知扰动与非对称输入饱和的非线性多智能体系统,提出基于预估器的神经动态面输出一致控制策略.在设计预估器的基础上构造预估误差,驱动神经网络更新权值估计系统未知动态,并将预估器与神经网络应用于非线性扰动观测器来补偿广义扰动.本文所提出的控制策略采用神经网络权值范数学习方法,减少学习参数数目.对于非对称的输入饱和,设计辅助系统,其生成的辅助变量与反步法相结合补偿输入限制.结合图论知识和Lyapunov函数等技术,证明多智能体系统的输出一致跟踪误差以及闭环系统中的所有信号最终有界.最后通过一组四旋翼飞行器和数值仿真验证提出控制策略的有效性.     

Chloride diffusivity in flexural cracked Portland cement concrete and fly ash concrete beams

In order to examine the effect of load-induced transverse cracks on the chloride penetration in flexural concrete beams, two different concretes, Portland cement concrete（PCC） and fly ash concrete（FAC）, were tested with various crack widths. Total 14 reinforced concrete（RC） beams, ten of which were self-anchored in a three-point bending mode, were immersed into a 5% NaCl solution with the condition of dry-wet cycles. Then, the free chloride ion contents were determined by rapid chloride testing（RCT） method. Based on the proposed analytical models of chloride penetration in sound and cracked concrete subjected to dry-wet cycles, the apparent chloride diffusion coefficient and chloride diffusivity of concrete were discussed. It can be found that the performance of chloride diffusivity in both concretes will be improved with the increase of crack width, and that the influence of convection action will also be augmented. Based on the two samples obtained in sound concrete after 15 and 30 cycles, the time-exponent, m, for chloride diffusion coefficient was determined to be 0.58, 0.42, 0.62 and 0.77 for PCC1, PCC2, FAC1 and FAC2 specimens, respectively. Finally, two influencing factors of fly ash content and crack width on chloride diffusivity were obtained by regression analysis of test data, and it can be seen that factors kf and kw can be expressed with quadratic polynomial functions of fly ash content, f, and crack width, w, respectively.