Vibration of Machine

Hi friends,

I have to model the structure for foundation of machine. The structure is only beam column and I need to input the vibration of machine on top. I assumed the vibration is 30% of machine' weight (4 ton). And I devided by 4 because each machine are supported by 4 columns.

I have followed the example problem 16 but the resulted moment for beam is quite strange. The moment is not like a sagging and hogging.


************************************************************************************
DEFINE TIME HISTORY DT 0.0013888
TYPE 1 FORCE
0 0 0.1 60 0.2 120 0.3 180 0.4 240 0.5 300 0.6 240 0.7 180 0.8 120 0.9 60
1 0
TYPE 2 FORCE
0 0 0.1 120 0.2 240 0.3 360 0.4 480 0.5 600 0.6 480 0.7 360 0.8 240 0.9 120
1 0
ARRIVAL TIME
0

***********************************************************************************

LOAD 1 LOADTYPE None  TITLE DEAD
SELFWEIGHT Y -1
MEMBER LOAD
9 11 13 15 18 22 25 29 31 33 35 37 64 TO 68 74 TO 78 83 TO 87 93 TO 97 181 -
183 184 186 UNI GY -4.57
11 13 21 28 33 35 69 TO 73 88 TO 92 182 185 UNI GY -4.32
LOAD 2 LOADTYPE None  TITLE LIFE
ELEMENT LOAD
101 TO 180 PR GY -2.5
LOAD 6 LOADTYPE None  TITLE VIB
SELFWEIGHT X 1
SELFWEIGHT Z 1
TIME LOAD
2 8 10 16 18 24 26 32 FX 1 1 1.000000
TIME LOAD
4 6 12 14 20 22 28 30 FX 2 1 1.000000
TIME LOAD
2 8 10 16 18 24 26 32 FZ 1 1 1.000000
TIME LOAD
4 6 12 14 20 22 28 30 FZ 2 1 1.000000
***********************************************************************************
LOAD COMB 3 1.4D+VIB
1 1.4 6 1.0
LOAD COMB 4 1.2D+1.6L+VIB
1 1.2 2 1.6 6 1.0
LOAD COMB 5 D+L+VIB
1 1.0 2 1.0 6 1.0
PERFORM ANALYSIS
DEFINE ENVELOPE
3 4 ENVELOPE 1 TYPE STRESS
END DEFINE ENVELOPE
FINISH

 

Do I have a correct assumption about this? Is there any command that I missed?

Please help me on this problem.

 

Thanks and Regards

Yusak