问题 单项选择题

某受压杆件,在支座不同、其他条件相同的情况下,其临界力最小的支座方式是()。

A.两端铰支 

B.一端固定,一端铰支 

C.两端固定 

D.一端固定,一端自由

答案

参考答案:D

解析:

临界力Pij的大小与下列因素有关:(l)压杆的材料:钢柱的Pij比木柱大,因为钢柱的弹性模量E大;(2)压杆的截面形状与大小:截面大不易失稳,因为惯性矩I大;(3)压杆的长度1:长度大,Pij小,易失稳;(4)压杆的支承情况:两端固定的与两端铰接的比,前者Pij大。不同支座情况的临界力的计算公式为:,l0称压杆的计算长度。当柱的一端固定一端自由时,l0=2l;两端固定时,l0=0.5l;一端固定一端铰支时,l0=0.7l;两端铰支时l0=l。

考点

建筑结构工程的可靠性

写作题

第二节 读写任务(共1小题,满分25分)

阅读下面的短文,然后按照要求写一篇150词左右的英语短文。

Beijing is set to lift its12-year-old ban on fireworks for the traditional Spring Festival holidays, probably starting from next Chinese Lunar New Year in January 2006.

Zhou Jidong, director of the Legislative Affairs Office of the Beijing municipal government(市政府), told a press conference last Thursday that his office has completed the draft(草案) regulations on firework safety supervision.

Under the draft regulations , setting off fireworks will be allowed in the capital city’s eight downtown districts from the Eve of the Lunar New Year to Lantern Festival 15 days later. When the draft regulations were posted on the municipal government’s website for suggestions, local residents gave a total of 969 pieces of advice, with 70 per cent in favour of lifting the ban. Related surveys suggest local people who want to light fireworks during Spring Festival range from 50.4 per cent to 86.3 per cent.

In fact, the voice of opposition and criticism has never ended since the municipal government introduced the ban in 1993, considering pollution, noise, fire worries and personal injuries caused by letting off fireworks.

Opponents accused the government of introducing the ban only for the sake of facilitating its management role while disregarding the will of the people. Worse, they say, the ban threatened to break down the age—old traditions of celebrating Spring Festival among Chinese people.

Partly due to this endless objection, about 106 out of a total 282 Chinese cities that had followed Beijing’s lead in banning fireworks have already dropped the ban.

[写作内容]

1.概括短文的内容要点,该部分的字数大约30词左右;

2.就“should the ban be lifted”这个主题发表你的看法,至少包含以下的内容要点,该部分的字数大约120词左右;

1)解禁的利弊;

2)你的看法如何;

3)你有什么建议?

[写作要求]

你可以使用实例或其他论述方法支持你的论点,也可以参照阅读材料的内容,但不要抄袭阅读材料中的句子。

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单项选择题