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Re: earthquake in STAAD-III

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-----Original Message-----
From: Vincenzo Valerio <enmar(--nospam--at)etheron.net>
To: seaint(--nospam--at)seaint.org <seaint(--nospam--at)seaint.org>
Date: sobota, december 12, 1998 1:08
Subject: RE: earthquake in STAAD-III


>What you did is OK.
>If you have got different loads is also OK. Remember that a time history
>analysis and response spectrum are dynamic analysis and UBC does a static
>analysis.
>UBC should be more conservative and also more expensive.


No, it can't be OK. I've tested everything on this simple example:

  ------------------
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----                 ----
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When I compare UBC and SPECTRUM results, absolute values are similar, but
diagram shapes are different. In SPECTRUM moments are constant along
members, and in UBC moments are changing sign - in the middle of every
member value is 0 (that's OK. I think - cracks are always close to joints).

With GROUND MOTION moments are 4-5 times greater then with UBC or SPECTRUM,
and moments are constant (like in SPECTRUM).

Here is input file (to perform time history analysis remove * from load 3):

STAAD PLANE QUAKE TEST
UNIT METER KNS
JOINT COORDINATES
1 0. 0.; 2 0. 2.; 3 0. 4.; 4 0. 6.
5 4. 0.; 6 4. 2.; 7 4. 4.; 8 4. 6.
MEMBER INCIDENCES
1 2 6; 2 3 7; 3 4 8
4 1 2; 5 2 3; 6 3 4
7 5 6; 8 6 7; 9 7 8
MEMBER PROPERTY EUROPEAN
4 TO 9 PRI YD .3 ZD .3
1 2 3 PRI YD .5 ZD .3
CONSTANT
E CONCRETE ALL
SUPPORT
1 5 FIXED
DEFINE UBC LOAD
ZONE 0.4 I 1. RWX 12. S 1.2
MEMBER WEIGHT
1 2 3 UNI -5.
DEFINE TIME HISTORY
TYPE 1 ACCELERATION
*EARTHQUAKE IN PETROVAC
0. 0. 0.08 -1.733 0.2 0. 0.38 2.6 0.52 -2. 0.58 -0.75 0.72 -2.362
0.8 0.5 0.88 -0.981 1.04 4.019 1.16 -2.348 1.26 -2.64
LOAD 1 UBC
UBC LOAD X
LOAD 2 SPECTRUM
MEMBER LOAD
1 2 3 UNI GY -5.
1 2 3 UNI GX 5.
SPECTRUM CQC X 1. ACC DAMP .05
*PETROVAC
0. 0.; 0.08 -1.733; 0.2 0.; 0.38 2.6; 0.52 -2.; 0.58 -0.75; 0.72 -2.362;
0.8 0.5; 0.88 -0.981; 1.04 4.019; 1.16 -2.348; 1.26 -2.64
*LOAD 3 GROUND MOTION
*MEMBER LOAD
*1 2 3 UNI GY -5.
*1 2 3 UNI GX 5.
*GROUND MOTION  X  1  1
PERFORM ANALYSIS
PRINT MEMBER FORCES ALL
FINISH