Clarification of Deformational Mechanism of Concrete by Laser Speckle Method

本研究应用激光散斑法这一非接触式的二维位移测量方法，对混凝土作为结构材料和结构构件的非线性变形行为进行了观测。为了研究混凝土作为结构材料的非线性变形，对高强砂浆制成的模型粗骨料素混凝土板试件进行了循环加载试验。在试验系列I中，每个试件布置了14个圆形模型骨料，观察到垂直于加载或开裂方向的残余变形较大，但随加载循环的增加很小。然而，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。在试验系列II中，在每个试件的中心放置一个正方形模型骨料，以调查…的效果骨料与混凝土之间的界面更多地取决于混凝土的变形特性。首先观察到引起滑移和张开位移的界面处的分离，然后砂浆裂缝从靠近加载边缘的集料拐角处扩展。在分离发生之前，试件的刚度接近于假设界面处有理想粘结的情况下的非线性有限元计算的刚度。当界面处无粘结时，试件的刚度逐渐减小，接近计算的刚度。认为剥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。利用剪切跨度四角点的移动测量试件剪跨的剪切变形。纵向配筋刚度较小的试件剪切变形较大，这是配筋率和杨氏模数的乘积。当剪跨的弯曲变形被定义为总变形减去实测剪切变形时，可以说由桁架类比得到的下述模型可以预测变形。考虑弯矩移位的常规方法--Branson法可以预测其弯曲变形。利用测得的主压应力方向和测得的力矩臂长，即纵向拉力和压力之间的距离，可以计算出弯矩位移。剪切变形可以作为斜拉杆和压杆变形引起的桁架变形的一部分来计算。拉杆的刚度假定为受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为受剪钢筋的刚度。较少

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