问题 单项选择题

某雨篷如题图所示,雨篷板上承受均布荷载(包括自重)q(设计值),在雨篷自由端沿板宽方向每米承受活荷载P(设计值),雨篷梁的截面尺寸为200mm×500mm,计算跨度l0=5m,混凝土强度等级为C30,纵向钢筋为HRB335,箍筋为HPB235,as=35mm。

设雨篷梁的受压区高度x=101mm,受扭计算中沿截面周边配置的箍筋单肢截面面积Astl与箍筋间距的比值为0.3,Uwr=1200mm,已知受扭纵筋最小配筋率为0.23%,受扭纵筋与箍筋的配筋强度比值为ζ=1.2,则截面纵向钢筋的总用量(抗弯及抗扭钢筋之和)的计算值与()项数值最为接近。

A.1356mm2

B.1221mm2

C.1271mm2

D.965mm2

答案

参考答案:C

解析:

混凝土强度:C30 fcu,k=30.0N/mm2 fc=14.33N/mm2 ft=1.43N/mm2

钢筋强度:fy=300N/mm2 f’y=300N/mm2 Es=200000N/mm2

截面有效高度:h0=465mm

正截面受弯配筋计算:

配筋率

受弯纵筋最小配筋率:

ρmin=max{0.20%,0.45ft/fy}=max{0.20%,0.21%}=0.21%<ρ=1.04%

受扭计算中取对称布置的全部纵向非预应力钢筋截面面积Astl可由下式求得:

剪扭构件中纵筋的最小配筋面积:

已知受扭纵筋最小配筋率ρtl,min=0.23

腹板受扭纵筋最小配筋面积Astl,mintl,min×b×h=230mm2<Astl

纵向钢筋总面积:965+302=1267mm2

单项选择题
阅读理解

阅读理解

     The practice of magic includes special words, actions, and objects. Most magic involves a person

called a magician, who claims to have supernatural powers.  

     Magic words. To work most magic, the magician sings or speaks special words in a certain order.  

These words are called incantations or spells. Some spells form prayers to demons(魔鬼), spirits, or

other supernatural forces. Many societies believe the magic will not work unless the magician recites the

spells perfectly. Other magic words have no meaning, though they supposedly possess power when

spoken by a magician.

     Magic actions accompany the words spoken in performing much magic. Many of these movements

act out the desired effect of the magic. For example, a magician trying to make rain fall may sprinkle

(洒) water on the ground. The magician's combined words and actions form a ceremony.

     Magic objects include certain plants, stones, and other things with supposed supernatural powers. 

Any such object may be called a fetish(物神). But this term often refers to an object-for example, a

carving or a dried snake-honored by a tribe for its magic powers. Many tribes believe fetishes have

magic power because spirits live in these objects.

     Many people carry magic objects called amulets(护身符)to protect themselves from harm. Many

amulets are stones or rings engraved(雕刻) with magic symbols.

     The magician.  In some societies, nearly everyone knows how to work some magic. In other

societies, only experts practice magic. Magicians may be called medicine men, medicine women,

shamans, sorcerers, or witch doctors. In many societies, magicians must inherit their powers. In others,

any person may become a magician by studying the magical arts.

     Many societies believe magicians must observe certain rules and taboos (forbidden actions) for their

spells to work. For example, they may be required not to eat various foods or to avoid sexual activity

for a certain period before the ceremony.

1. What do magic words mean to people in some society?

A. They have the power to kill devils.

B. They have power if magician recites the right spells.

C. They have no effect at all.  

D. They can be used whenever they want.  

2. People believe magic actions will have an effect if they are accompanied by________.

A. the spells

B. magic objects

C. stones or rings engraved with magic symbols

D. medicine 

3. Why do many people believe in a fetish? 

A. Because it is often a ring which is worth a lot of money.  

B. Because it is carved with magic symbols.  

C. Because people think spirits live in it.  

D. Because it can help them with many things.

4. What's the best title of the passage?

A. How Magic Works

B. The Power of Magic

C. How to Practice Magic

D. The Choice of Magicians