问题 单项选择题 案例分析题

图34-35(Z)所示的框架为某框架-剪力墙结构中的一榀边框架,其抗震等级为二级,底部一、二层顶梁截面高度为700mm,梁顶与板顶平,柱截面为700mm×700mm。已知在重力荷载和地震作用下,柱BC的轴压比为0.75,节点B和柱BC未按“强柱弱梁”调整的组合弯矩设计值(kN·m)如图34-35(Z)所示。

提示:①对应于地震作用标准值,各层框架承担的剪力均不小于结构总剪力的20%;②按《高层建筑混凝土结构技术规程》JGJ3-2010作答。

试问,底层柱BC的纵向配筋计算时,考虑地震组合的弯矩设计值(kN·m)与下列何项数值最为接近()。

A.450

B.470

C.680

D.700

答案

参考答案:B

解析:

根据《高规》第6.2.1条,二级框架(其他结构中)η=1.2,

∑M=η∑M=1.2×(560+120)=816kN·m

根据《高规》第6.2.2条及条文说明:底层柱纵向钢筋应根据上、下端的不利情况配置。

M>M,所以计算弯矩取M,故B最接近。

【命题思路】

本题主要考查钢筋混凝土框架“强柱弱梁”的内力调整要求,以及框架结构和其他类型框架的不同内力调整方法。

【解题分析】

1.由于钢筋混凝土框架柱的延性通常比梁的延性小,而框架柱形成塑性铰会对结构承受垂直荷载产生较大影响,因而在框架柱设计中,通过有目的地增大柱端弯矩设计值,体现“强柱弱梁”的抗震设计概念。

2.不同的框架抗震等级及不同的框架(如框架结构中的框架和框架-剪力墙结构中的框架)采用不同的柱端弯矩增大系数,以体现框架柱不同的抗震性能要求。

3.本框架属于框架-剪力墙结构中的二级框架,根据《高层建筑混凝土结构技术规程》JGJ3-2010第6.2.1条和第6.2.2条,可以得到正确的选项。

选择题
阅读理解
阅读下面短文根据其内容完成信息记录表。
    Summer vacation can be a relaxing time for sleeping, eating good meals and seeing old friends.
Try to take some time off from school and spend a few weeks of fun. Here are some ideas for
planning your vacation.
    First of all, joining a club is a good choice! We have a music club, a sports club and an art club.
It's good for your future development and the teachers in the club can give you good advice. Just
call 866-6489 for more information.
    Doing something good for society is also great. Here we offer a volunteer program to you. You
know that teens can also make the world better. If you want to be a volunteer, you can call us
between Monday and Friday at 866-6847.
    Have you ever had the experience of living with another family? Here's a program called "Meeting
a New Family". Two families exchange their children for a period of time. Isn't that exciting? Join us!
    Summer camps are still popular today. We are going to hold an English summer camp this year.
You can not only make friends but also improve your English at summer camp. You can practice
English by playing different games, speaking in speech contests and so on. Do you like the idea?
Call us at 866-8746.
ProgramWhat you can do
ClubYou can join an art club, a sports club or a 1              club.
VolunteerYou can call at 2              from Monday to Friday if you want to do
something good for society.
Meeting a New FamilyYou will have a chance to 3               with a new family for a certain time.
Summer Camp You can not only make 4               but also improve your English.
The text is mainly about some ideas for 5              .