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问题 单项选择题

某18m预应力混凝土屋架下弦拉杆，截面构造如图所示。采用后张法一端张拉施加预应力，并施行超张拉。预应力钢筋选用2束低松弛钢绞线(Ap=840mm2)，非预应力钢筋为HRB400级钢筋，C45级混凝土。采用夹片式锚具(有顶压)，孔道成型方式为预埋金属波长管，张拉控制应力σcon=0.65fptk，fptk=1720N/mm2，预应力筋、非预应力钢筋的弹性模量分别为Es1=1.95×105N/mm2，Es2=2.0×105N/mm4，混凝土弹性模量Ec=3.35×104N/mm2。

第一批预应力损失值σlⅠ（N/mm2），与下列何项数值最为接近（）

A．68.6

B．76.1

C．80.0

D．84.4

答案

参考答案：D

解析：

查《混凝土结构设计规范》表10.2.2，取a=5mm

由规范式(10.2.2)：

σcon=0.65fptk=0.65×1720=1118N/mm2

查《混凝土结构设计规范》表10.2.4，取κ=0.0015；μθ=0.0

κx+μθ=0.0015×18=0.027＜0.2，则：

σl2=(κx+μθ)σcon=0.027×1118=30.186N/mm2

故

σlⅠ=σl1+σl2=54.167+30.186=84.353N/mm2

阅读理解

阅读理解。

     Sam likes eating fish very much. He often buys fish in the shop and takes them home. One day his wife

sees the fish and thinks, "Good! Now, I can ask my friends to have lunch and we can eat the fish. They like

fish very much." 　　

     When Sam comes home from work in the evening, the fish is not there and his wife says, "Oh, your cat

eats it. "And then she gives him some bread for his supper. Sam is angry (生气). He takes the cat and his wife

to a shop near his house and weighs (称) the cat. Then he turns to his wife and says, "My fish weighs one kilo.

The cat weighs one kilo, too. My cat is here, you see, then, where is my fish?"

1. What does Sam like eating very much? 　

    ______________________________________　

2. Who eat the fish that day? 　

    ______________________________________　

3. How much does the fish weigh? 　

    ______________________________________　

4. What does Sam's wife give him for supper? 　

    ______________________________________

5. Can you guess if (是否) Sam knows where the fish is? 

    ______________________________________
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单项选择题 A1型题

WHO称（）是严重威胁人类生命的20世纪瘟疫.

A.饮酒

B.吸烟

C.AIDS

D.细菌感染

E.病毒感染
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