问题 单项选择题

某二级干线公路上一座标准跨径为30m的单跨简支梁桥,其总体布置如图所示。桥面宽度为12m,其横向布置为:1.5m(人行道)+9m(车行道)+1.5m(人行道)。桥梁上部结构由5根各大29.94m,高2.0m的预制预应力混凝土T型梁组成,梁与梁间用现浇混凝土连接;桥台为单排排架桩结构,矩形盖梁、钻孔灌注桩基础。设计荷载:公路—Ⅰ级、人群荷载3.0kN/m2

假定,前述桥梁主梁结构自振频率(基频)f=4.5Hz。试问,该桥汽车作用的冲击系数μ与下列何项数值(Hz)最为接近().

A.0.05

B.0.25

C.0.30

D.0.45

答案

参考答案:B

解析:

解答如下:

根据《公路桥涵设计通用规范》4.3.2条规定:

μ=0.1767ln4.5-0.0157=0.25

阅读理解

阅读理解。

   The common cold is the world's most widespread illness, which is plagues (疫病) that people receive.

   The most widespread fallacy (谬误) of all is that colds are caused by cold. They are not. They are

caused by viruses(病毒) passing on from person to person. You catch a cold by coming into contact,

directly or indirectly, with someone who already has one. If cold causes colds, it would be reasonable

to expect the Eskimos to suffer from them forever. But they do not. And in isolated arctic regions

explorers have reported being free from colds until coming into contact again with infected people from

the outside world by way of packages and mail dropped from airplanes.

     During the First World War soldiers who spent long periods in the trenches (战壕), cold and wet,

showed no increased tendency to catch colds. In the Second World War prisoners at the Auschwitz

Concentration Camp (奥斯维辛集中营), naked and starving, were astonished to find that they seldom

had colds. At the Common Cold Research Unit in England, volunteers took part in experiments in which

they gave themselves to the discomforts of being cold and wet for long stretches of time. After taking hot

baths, they put on bathing suits, allowed themselves to be with cold water, and then stood about dripping wet (湿透) in drafty (通风的) room. Some wore wet socks all day while others exercised in the rain

until close to exhaustion. Not one of the volunteers came down with a cold unless a cold virus was

actually dropped in his nose.

    If, then, cold and wet have nothing to do with catching colds, why are they more frequent in the

winter? Despite the most pains-taking research, no one has yet found the answer. One explanation

offered by scientists is that people tend to stay together indoors more in cold weather than at other time,

and this makes it easier for cold viruses to be passed on.

    No one has yet found a cure for the cold. There are drugs and pain suppressors(止痛片) such as

aspirin, but all they do is relieve the symptoms.

1. The writer offered _______ examples to support his argument.

A. 4            

B. 5              

C. 6              

D. 3

2. Arctic explorers may catch colds when _______.

A. they are working in the isolated arctic regions

B. they are writing reports in terribly cold weather

C. they are free from work in the isolated arctic regions

D. they are coming into touch again with the outside world

3. Volunteers taking part in the experiments in the Common Cold Research Unit probably _______.

A. suffered a lot                      

B. never caught colds

C. often caught colds                  

D. became very strong

4. The passage mainly discusses _______.

A. the experiments on the common cold

B. the fallacy about the common cold

C. the reason and the way people catch colds

D. the continued spread of common colds

单项选择题