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三道
1、某两层钢筋混凝土框架,集中于楼盖和屋盖处的重力荷载代表值相等
,每层层高皆为4.0m,各层的层间刚度相同;G,G,1200kN,D,,D,8630kN/m1212
?类场地,设防烈度为7度,设计基本地震加速度为0.10g,设计分组为第二组,
结构的阻尼比为。 ,,0.05
(1)求结构的自振频率和振型,并验证其主振型的正交性
(2)试用振型分解反应谱法计算框架的楼层地震剪力 解1):(1)计算刚度矩阵
k,k,k,8630,2,17260kN/m1112
k,k,,k,,8630kN/m12212
k,k,8630kN/m222
(2)求自振频率
122 ,,[(mk,mk),(mk,mk),4mm(kk,kk)]1,212221112221112112212212mm12
1,[(120,8630,120,17260),2,120,120
22(120,8630,120,17260),4,120,120[(17260,8630,(,8630)]
,27.47/188.28
,,5.24rad/s,,13.72rad/s12
(3)求主振型
当 ,,5.24rad/s1
22Xm,k1205.24172601.618,,,121111 ,,,86301Xk,1112
当 ,,13.72rad/s2
2212013.72172600.618,Xm,k,,,221211 ,,,86301Xk,2112
(4)验证主振型的正交性
质量矩阵的正交性
T1.00012001.000,,,,,,T {X}[m]{X},,0,,,,12,,1.6180120,0.618,,,,,,
刚度矩阵的正交性
T1.00017260,86301.000,,,,,,T {X}[k]{X},,0,,,,12,,1.618,86308630,0.618,,,,,,
解2):由表3.2查得:?类场地,第二组,T=0.40s g
由表3.3查得:7度多遇地震 ,,0.08max
,2第一自振周期 T,,1.200s,T,T,5T1g1g,1
,2第二自振周期 T,,0.458s,T,T,5T2g1g,2
(1)相应于第一振型自振周期的地震影响系数: T1
0.90.9T,,0.40,,g,, ,,,,,0.08,0.030,,1max,,T1.200,,1,,
第一振型参与系数
n
,mii1,1200,1.000,1200,1.618i,1, ,,,0.72412221200,1.000,1200,1.6182m,ii1,i,1
于是: F,,,,G,0.030,0.724,1.000,1200,26.06kN1111111
F,,,,G,0.030,0.724,1.618,1200,42.17kN1211122
第一振型的层间剪力:
V,F,42.17kN1212
V,F,F,68.23kN111112
T (2)相应于第二振型自振周期的地震影响系数: 2
0.90.9T,,0.40,,g,, ,,,,,0.08,0.071,,2max,,T0.458,,,,2
第二振型参与系数
n
,mii2,1200,1.000,1200,(,0.618)i,1, ,,,0.27622221200,1.000,1200,(,0.618)2m,ii2,i,1
于是: F,,,,G,0.071,0.276,1.000,1200,23.52kN2122211
F,,,,G,0.071,0.276,(,0.618),1200,,14.53kN2222222
第二振型的层间剪力:
V,F,,14.53kN2222
V,F,F,8.99kN212122
(3)由SRSS法,计算各楼层地震剪力:
2222 V,V,42.17,(,14.53),44.60kN,j22j,2
2222 V,V,68.23,8.99,68.821kN,j11j,2
2、某两层钢筋混凝土框架,集中于楼盖和屋盖处的重力荷载代表值相等
,每层层高皆为4.0m,框架的自振周期;各层的层间刚G,G,1200kNT,1.028s121
T,0.40s, ,,0.08)度相同,D,,D,8630kN/m;?类场地,7度第二组(,结构12gmax
的阻尼比为,试按底部剪力法计算框架的楼层地震剪力,并验算弹性层间,,0.05
,,位移是否满足要求(,,1/450)。 e
解:(1)求结构总水平地震作用:
0.90.9T,,0.40,,g,, ,,,,,0.08,0.033,,1max,,T1.028,,1,,
F,,G,0.033,0.85(1200,1200),67.32kNEk1eq
(2)求作用在各质点上的水平地震作用
T,1.028s,1.4T,1.4,0.4,0.56s1g
,,0.08T,0.01,0.08,1.028,0.01,0.092n1
,F,,F,0.092,67.32,6.2kNnnEk
GH11 F,F(1,,)1Eknn
GHjj,,j1
1200,4 ,,67.32(1,0.092),20.37kN1200,4,1200,8
GH22 F,F(1,,),,F2Eknnn
GHjj,,j1
1200,8 ,,67.32(1,0.092),6.2,46.95kN1200,4,1200,8(3)求层间剪力
V,F,F,20.37,46.95,67.32kN112
V,F,46.95kN22
(4)验算层间弹性位移
,,67.32/8630,0.0078m,7.8mm 1
(满足) ,,7.8/4000,1/512,1/4501
,,46.95/8630,0.00544m,5.44mm1
,,5.44/4000,1/735,1/450 (满足) 1
3、某三层钢筋混凝土框架,集中于楼盖处的重力荷载代表值分别为
,,每层层高皆为5.0m,层间侧移刚度均为40MN/m,G,G,1000kNG,600kN123
框架的基本自振周期;?类场地,8度第二组,设计基本加速度为0.30g,T,0.6332s1
结构的阻尼比为,试按底部剪力法计算框架的楼层地震剪力,并验算弹性,,0.05
层间位移是否满足规范要求。
(1)求结构总水平地震作用:
0.90.9T,,0.30,,g,, ,,,,,0.24,0.122,,1max,,T0.6332,,,,1
F,,G,0.122,0.85(1000,1000,600),269.6kNEk1eq
(2)求作用在各质点上的水平地震作用
T,0.6332s,1.4T,1.4,0.3,0.42s1g
,,0.08T,0.07,0.08,0.6332,0.07,0.121n1
,F,,F,0.121,269.6,32.62kNnnEk
GH11 F,F(1,),1Eknn
GH,jj,j1
1000,5 ,,269.6(1,0.121),49.37kN1000,5,1000,10,600,15
GH22 F,F(1,),2Eknn
GH,jj,j1
1000,10 ,,269.6(1,0.121),98.75kN1000,5,1000,10,600,15
GH33 F,F(1,),,F,3Eknnn
GH,jj,j1
600,15,,269.6(1,0.121),32.62,88.87,32.62,121.49kN1000,5,1000,10,600,15
(3)求层间剪力
V,F,F,F,49.37,98.75,121.49,269.6kN1123
V,F,F,98.75,121.49,220.24kN223
V,F,121.49kN33
(4)验算弹性位移
3V269.6,1051 ,,,,0.0063,[,]H,,0.0091e6K40,105501
满足规范要求