Clarification of Deformational Mechanism of Concrete by Laser Speckle Method

本研究利用激光散斑法这一非接触式的二维位移测量方法，对混凝土结构材料和构件的非线性变形行为进行了观测，研究了混凝土结构材料的非线性变形，采用高强砂浆配制模型粗骨料，对素混凝土平板试件进行了低周反复荷载试验。作为测试系列I的结果，其中14个圆形模型骨料被安排在每个样本中，它被观察到，在垂直于加载或开裂的方向上的残余变形是相当大的，但随着加载循环增加很少。在加载方向上的残余变形，但是，被发现是相当小的，但随着加载循环稳定增加。试验系列II，其中一个正方形模型骨料被放置在每个试样的中心，进行调查的影响 关于我们 骨料与砂浆界面对混凝土变形特性的影响。首先观察到界面处的分离引起滑移和张开位移，然后砂浆裂缝从靠近加载边缘的骨料角部发展。在分离发生之前，试样的刚度接近于由非线性有限元方法计算的刚度的情况下，假设在界面处的完美结合。试件的刚度逐渐减小，并接近于假设界面无粘结时的计算刚度。试验结果表明，砂浆的开裂不仅随着荷载的增加而发展，而且随着荷载循环次数的增加而发展。利用剪切跨四个角点的位移测量了试件剪切跨的剪切变形。较大的剪切变形观察到与一个较小的刚度的纵向钢筋，这是一个产品的配筋率和杨氏模量的标本。当剪切跨的弯曲变形被定义为总变形减去测量的剪切变形时，可以说从桁架类比导出的以下模型预测了变形。弯曲变形可以用传统的Branson方法来预测，考虑了弯矩的变化。利用测得的主压应力方向和测得的力臂长度（纵向拉力和压缩力之间的距离）计算弯矩位移。剪切变形可以作为斜拉压杆变形引起的桁架变形的一部分来计算。拉压杆的刚度被假定为抗剪钢筋的刚度加上周围混凝土的抗拉刚度，并随着荷载的增加逐渐减小到单独的抗剪钢筋的刚度。少

In this research the laser speckle method, which is a non-contact type of measuring method for two dimensional displacements with accuracy of mum, was applied to observe non-linear deformational behavior of concrete as structural material and structural member.To investigate non-linear deformation of concrete as structural material, plate specimens of plain concrete with model coarse aggregate which was made of high strength mortar were tested with cyclic loadings. As a result of test series I in which 14 circular model aggregates were arranged in each specimen, it was observed that residual deformations in the direction vertical to the loading or to cracking were rather large but increased little with the loading cycles. Residual deformations in the direction of the loading, however, was found to be rather small but to increase steadily with loading cycles. Test series II,in which one square model aggregate was placed at the center of each specimen, was conducted to investigate effect … More of the interface between aggregate and morter on deformational characteristics of concrete. Separation at the interface which caused slip and opening displacements was first observed, then mortar crack was developed from the corners of the aggregate near the loading adges. Before the separation occurred, stiffness of the specimen was close to the stiffness calculated by a non-linear finite element method for the case where perfect bond was assumed at the interface. The specimen stiffness gradually decreased and approached to the calculated stiffness for the case where no bond was assumed at the interface. It was considered that the separation and the mortar cracking were developed not only with increase of load but also with increase of loading cycles.Beam specimens with shear reinforcement were tested under monotonic loading. Shear deformations of a shear span of the specimen were measured by using movement of points at the four corner of the shear span. Greater shear deformations were observed with a specimen with a smaller stiffness of longitudinal reinforcement which is a product of the reinforcement ratio and the Young's modulus. When flexural deformations of the shear span were defined as the total deformations minus the measured shear deformations, it could be said that the following model derived from truss analogy predict the deformations. The flexural deformations could be predicted by the conventional method, Branson's method, considering the moment shift. The moment shift could be calculated by using the measured direction of the principal compressive stress and the measured moment arm length which is the distance between longitudinal tensile and compressive forces. The shear deformations could be calculated as a part of deformations of the truss which is induced by the deformations of the diagonal tension and compression struts. Stiffness of the tension strut was assumed to be stiffness of the shear reinforcement plus tension stiffness of the surrounding concrete and to be reduced gradually to the stiffness of the shear reinforcement alone with increase of load. Less