Clarification of Deformational Mechanism of Concrete by Laser Speckle Method

本文将激光散斑法作为一种非接触式二维位移测量方法，用于观察混凝土作为结构材料和构件的非线性变形行为。为研究混凝土作为结构材料的非线性变形，采用高强度砂浆制成模型粗骨料素混凝土板试件进行了循环加载试验。通过在每个试件中布置14个圆形模型集料的试验系列1，可以观察到，在垂直于加载或开裂方向上的残余变形较大，但随着加载周期的增加，残余变形的增加幅度不大。然而，在加载方向上的残余变形很小，但随着加载周期的增加而稳步增加。试验系列II，在每个试件的中心放置一个方形模型骨料，研究骨料与砂浆之间的界面对混凝土变形特性的影响。首先观察到界面处的分离导致滑移和张开位移，然后在加载边缘附近的骨料角处出现砂浆裂缝。分离发生前，试件的刚度接近于采用非线性有限元法计算的界面完美粘结情况下的刚度。试件刚度逐渐减小，接近于界面处无粘结情况下的计算刚度。认为分离和砂浆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。采用剪切加筋梁试件进行单调加载试验。试样的剪切变形是通过在剪切跨度的四个角的点的运动来测量的。当试件的纵向配筋刚度（配筋率与杨氏模量的乘积）较小时，试件的剪切变形较大。当剪切跨的弯曲变形定义为总变形减去实测剪切变形时，可以认为，由桁架类比导出的以下模型可以预测变形。挠曲变形可以通过考虑矩移的传统方法布兰森方法来预测。用测得的主压应力方向和测得的力臂长度（即纵向拉伸力和纵向压缩力之间的距离）可以计算出弯矩位移。剪切变形可以计算为桁架变形的一部分，而桁架变形是由斜拉杆和压杆变形引起的。假设受拉支撑刚度为受剪钢筋刚度加周围混凝土受拉刚度，并随着荷载的增大逐渐减小为仅受剪钢筋刚度。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