土木工程专业英语第8次课讲义
讲义主编：李国良
副主编：刘福雨 李博 段鹏程  柯志林
参编：全体土木09.1同学
Chapter 7 土木工程专业文献选读
Lesson 3  Prestressed Concrete
预应力混凝土
Objectives（教学目标）：本课主要介绍预应力的概念和预应力混凝土方面的基本知识，同时也介绍了预应力混凝土的发展过程、特点以及应用，通过本课的学习，应掌握预应力混凝土的基本知识，掌握相关的专业词汇。
Key Issues（教学重点）：预应力混凝土的特点及适用范围。掌握专业词汇；掌握句子表达方式
  Lesson 3  Prestressed Concrete
教师补充Considering：
1. What is prestressing ？
“Prestressing” means the artificial creation of stresses in a structure before loading, so that the stresses which then exist under load are more favorable than would otherwise be the case.
reactor 翻译2.What is the concept of prestressed concrete？
(1)ACI-American Concrete Institute
Prestressed concrete may be defined as concrete in which internal stresses of such magnitude and distribution have been introduced that the stresses resulting from the given applied loading are counteracted to a desired degree.
预应力混凝土是根据需要人为地引入某一数值与分布的应力，用以部分或全部抵消外荷载应
力的一种加筋混凝土。
(2) Concept of  Prestressing concrete
“Prestressing concrete” means the artificial creation of stresses in concrete or reinforced concrete before loading, in which internal stresses of such magnitude and distribution have been introduced that the stresses resulting from the given applied loading are counteracted to a desired degree.
事先人为地在混凝土或钢筋混凝土中引入内部应力，
且其数值和分布恰好能将使用荷载产生的应力抵消到一个合适程度的配筋混凝土,称为预应力混凝土。
Translation（翻译）：
Paragraph 1
1. Concrete is strong in compression, but weak in tension: its tensile strength varies fro
m 8 to 14 percent of its compressive strength.
【学生翻译】：混凝土的抗压力高，但抗拉力低：其抗拉强度是抗压强度的百分之八到百分之十四不等。
compression ：抗压强度  tension ：抗拉强度
【教师补充】：混凝土抗压能力强，但抗拉能力低，抗拉强度仅为抗压强度的8%～14%。
tensile strength(抗拉强度)
compressive strength(抗压强度).  
2. Due to such a low tensile capacity, flexural cracks develop at early stages of loading.
【学生翻译】：由于抗拉承载力低，裂缝会在荷载作用早期阶段发展。
flexural cracks：裂缝
【教师补充】：由于抗拉承载力低，挠曲裂缝在受荷早期就会产生。
flexural(弯曲的、挠曲的) cracks(裂缝)
3. In order to reduce or prevent such cracks from developing, a concentric or eccentric force is imposed in the longitudinal direction of the structural element.
【学生翻译】为减少或防止这种裂缝的发展，在结构构件的纵向施加同心或偏心力。
longitudinal：纵向的
【教师补充】为了减小或防止裂缝的开展，可以沿结构构件的纵向施加一个轴心或偏心荷载。
concentric(同心的)   eccentric (偏心的)
structural element(结构构件).
4. This force prevents the cracks from developing by eliminating or considerably reducing the tensile stresses at the critical midspan and support sections at service load, thereby raising the bending, shear, and torsional capacities of the sections.
【学生翻译】在荷载作用下，这个力能够消除或大大减少跨中关键部位和支座截面的拉伸应力，从而减少裂缝的发展，提高截面的抗弯、抗剪以及抗能力。
midspan：跨中  section：截面
【教师补充】此荷载可消除或大大减小使用荷载在跨中和支座临界截面所产生的拉应力，从而控制了裂缝的开展，也提高了截面的抗弯、抗剪和抗扭能力。
Critical:在危机期中的、紧要关头的、转折点的
service load(使用荷载)   support（支座）
5. The sections are then able to behave elastically, and almost the full capacity of the concrete in compression can be efficiently utilized across the entire depth of the concrete sections when all loads act on the structure.
【学生翻译】这样，构件能表现出弹性性质，当全部荷载作用于结构时，混凝土构件的全部断面的抗压能力都能够被充分有效地发挥出来。
【教师补充】：这样，当所有荷载都施加于结构上时，截面仍会处于弹性状态，使几乎全截面混凝土的抗压能力都能得到充分利用。
elastically(弹性的),
Paragraph 2
1.Such an imposed longitudinal（纵向的） force is called a prestressing force（预应力）, i.e., a compressive force that prestresses the sections along the span of the structural element（结构构件） prior to（较早的、顺序在先的） the application of the transverse（横向的） gravity dead and live loads or transient(瞬时的) horizontal (水平的) live loads.
【学生翻译】这样一个强加的纵向力称为预应力,也就是说，是一种在受到横断面的重力恒荷载和活荷载作用或者是受到瞬间的水平活荷载作用之前，给沿着这个结构杆件跨度的截面上
施加预应力的压缩力。
prestressing force：预应力
生活中的预应力
【教师补充】这种沿纵向施加的力称为预应力，也就是构件在承受自重恒载、活载以及瞬时的水平活载之前就沿着跨度方向施加在构件截面上的预加压力。
i.e.—which is to say， in other words
2. The type of prestressing force involved, together with its magnitude, are determined mainly on the basis of the type of system to be constructed and the span length and slenderness desired.
【学生翻译】这个预应力的类型和它的大小主要以这个被构成体系的类型、跨长、设计的长细度为基础而被决定。
slenderness：长细度
【教师补充】预应力的形式与大小，主要取决于拟建结构体系的类型、跨径和长细比。
magnitude(数量、等级),   span length(跨径)
Slenderness: 细长的;薄弱
Slenderness ratio 长细比
3. Since the prestressing principle is applied longitudinally along or parallel to the axis of the member, the prestressing principle involved is commonly known as linear prestressing.
【学生翻译】由于这个预应力是纵向地沿着或者平行于这个杆件的中心轴，因此预应力原则上是被人俗称的线性预应力。

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