《混凝土结构设计原理》双语 (12).ppt

Chapter2 Main Physical and Mechanical Properties of Concrete and Reinforcing Steel 2.1 Properties of hardened concrete 2.2.1 Uniaxial compressive strength and Stress-strain curve in compression Flaws are attributable to a number of causes, the main ones being: Discontinuities in the cement paste （水泥胶体）owing to its complex morphology（形态） Voids caused by shrinkage（徐变） ， thermal movements and incomplete compaction (搅拌） Discontinuities at the boundary between aggregate （骨料）particles and the paste or mortar （砂浆） Stress concentration caused by flaws in concrete Illustration (例证） of the theory----------Strength and W/C ratio To hydrate（水化）, cement need about 38% water by weight of cement theoretically In practice, complete hydration of cement does not take place and is not aimed at. Only about 23% water by weight of cement is combined （结合） Non-evaporable water is 23% by weight of cement Spaces left after the loss of the evaporable water are collectively known as the voids The present of which is a great source of weakness The relation of water/cement ratio and concrete strength is intimately connected with the voids Failure process illustration of the theory------Transverse confine （侧向约束）can greatly increase axial compressive strength Spiral stirrups（螺旋箍筋） f=fc+4σr Steel tube concrete（钢管混凝土） Conclusions Flows are the source of cracking Concrete compressive strength is primarily depend on the water/cement ratio Concrete in the ‘critical’ zones of compression always fail by ‘splitting’ ---never by ‘crushing’ Transverse confine can greatly increase axial compressive strength Uniaxial compressive strength of three types of specimens: fcu, fc, fc’ Cube strength fcu (立方体强度） The dimension of cubic specimen is 150*150*150mm （or 100*100*100mm ） The test result of Cubic specimen is the base of strength grade （强度等级 C20；C30….）of concrete The frictional forces develop between the plates of the testing machine and the contact faces of the test specimen.