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1、Lesson PlanReviewNew Words and PhrasesReading and TranslatingUnit EightClassroom Exercises,Review a premature failure by diagonal tension the amount of cracking (width and number of cracks) is proportional to the strain,Unit Eight Safety of Structures 单 元 8 结构的安全度,The principal purpose of specificat
2、ions is to provide general principles and computational methods in order to verify safety of structures.,The principal purpose of specifications is to provide general principles and computational methods in order to verify safety of structures. 规范的主要目的是提供一般性的设计原理和计算方法，以便验算结构的安全性。,Failure has to be c
3、onsidered not only as overall collapse of the structure but also as unserviceability or, according to a more precise common definition, as the reaching of a limit state which causes the construction not to accomplish the task it was designed for. There are two categories of limit state:,Failure has
4、to be considered not only as overall collapse of the structure but also as unserviceability or, according to a more precise common definition, as the reaching of a limit state which causes the construction not to accomplish the task it was designed for. There are two categories of limit state:破坏不仅仅指
5、结构的整体破坏，而且还指结构不能正常使用，或者，用更为确切的话来说，把破坏看成是结构已经达到不能继续承担其设计荷载的“极限状态”。在结构设计中，通常有两类极限状态，即：,（1）Ultimate limit state, which corresponds to the highest value of the load-bearing capacity. Examples include local buckling or global instability of the structure; failure of some sections and subsequent transform
6、ation of the structure into a mechanism; failure by fatigue; elastic or plastic deformation or creep that cause a substantial change of the geometry of the structure; and sensitivity of the structure to alternating loads, to fire and to explosions.,（1）Ultimate limit state, which corresponds to the h
7、ighest value of the load-bearing capacity. Examples include local buckling or global instability of the structure; failure of some sections and subsequent transformation of the structure into a mechanism; failure by fatigue; elastic or plastic deformation or creep that cause a substantial change of
8、the geometry of the structure; and sensitivity of the structure to alternating loads, to fire and to explosions. (1)承载力极限状态，它相当于结构能够达到的最大承载能力。例如：结构的局部屈曲和整体不稳定性；某些截面失效，随后结构转变为机构；疲劳破坏；引起结构几何形状显著变化的弹性变形或塑性变形或徐变；结构对交变荷载、火灾和爆炸的敏感性。,（2）Service limit states, which are functions of the use and durability of
9、 the structure. Examples include excessive deformations and displacements without instability; early or excessive cracks; large vibrations; and corrosion.,（2）Service limit states, which are functions of the use and durability of the structure. Examples include excessive deformations and displacement
10、s without instability; early or excessive cracks; large vibrations; and corrosion. (2)正常使用极限状态，它对应着结构的使用功能和耐久性。例如：结构失稳前的过大变形和位移；早期开裂或过大的裂缝；较大的振动和腐蚀。,Computational methods used to verify structures with respect to the different safety conditions can be separated into: （1）Deterministic methods, in whi
11、ch the main parameters are considered as nonrandom parameters. （2）Probabilistic methods, in which the main parameters are considered as random parameters,Computational methods used to verify structures with respect to the different safety conditions can be separated into:（1）Deterministic methods, in
12、 which the main parameters are considered as nonrandom parameters.（2）Probabilistic methods, in which the main parameters are considered as random parameters 根据不同的安全度条件，可以把结构验算所采用的计算方法分成: （1）确定性的方法，在这种方法中，把主要参数看作非随机参数。（2）概率方法，在这种方法中，主要参数被认为是随机参数。,Alternatively, with respect to the different use of fa
13、ctors of safety, computational methods can be separated into:（1）Allowable stress method, in which the stresses computed under maximum loads are compared with the strength of the material reduced by given safety factors.,Alternatively, with respect to the different use of factors of safety, computati
14、onal methods can be separated into:（1）Allowable stress method, in which the stresses computed under maximum loads are compared with the strength of the material reduced by given safety factors.或者，根据安全系数的不同用途，可以把结构的计算方法分为:(1)容许应力法：在这种方法中，把结构承受最大荷载时的计算应力和经过特定安全系数折减后的材料强度作比较。,（2）Limit states method, in
15、 which the structure may be proportioned on the basis of its maximum strength. This strength, as determined by rational analysis, shall not be less than that required to support a factored load equal to the sum of the factored live load and dead load (ultimate state).,（2）Limit states method, in whic
16、h the structure may be proportioned on the basis of its maximum strength. This strength, as determined by rational analysis, shall not be less than that required to support a factored load equal to the sum of the factored live load and dead load .(2)极限状态法，在这种方法中，结构的工作状态是以其最大强度为依据来衡量的。由理论分析确定的（结构材料）最
17、大强度应不小于结构承受设计荷载所需要的强度。设计荷载等于乘以荷载系数的活载与恒载之和。,The safety factor, which according to modern trends is homogeneous and independent of the nature and combination of the materials used, can usually be defined as the ratio between the conditions yield failure of the construction and the worst predictable working conditions. This ratio is also inversely proportional to the probability of failure of the structure.,
